Reflecting Database Objects — SQLAlchemy 2.0 Documentation

Release: 2.0.39 | Release Date: March 11, 2025

# SQLAlchemy 2.0 Documentation

# Reflecting Database Objects

A `Table` object can be instructed to load information about itself from the corresponding database schema object already existing within the database. This process is called reflection. In the most simple case you need only specify the table name, a `MetaData` object, and the `autoload_with` argument:

    >>> messages = Table("messages", metadata_obj, autoload_with=engine)
    >>> [c.name for c in messages.columns]
    ['message_id', 'message_name', 'date']

The above operation will use the given engine to query the database for information about the `messages` table, and will then generate `Column`, `ForeignKey`, and other objects corresponding to this information as though the `Table` object were hand-constructed in Python.

When tables are reflected, if a given table references another one via foreign key, a second `Table` object is created within the `MetaData` object representing the connection. Below, assume the table `shopping_cart_items` references a table named `shopping_carts`. Reflecting the `shopping_cart_items` table has the effect such that the `shopping_carts` table will also be loaded:

    >>> shopping_cart_items = Table("shopping_cart_items", metadata_obj, autoload_with=engine)
    >>> "shopping_carts" in metadata_obj.tables
    True

The `MetaData` has an interesting “singleton-like” behavior such that if you requested both tables individually, `MetaData` will ensure that exactly one `Table` object is created for each distinct table name. The `Table` constructor actually returns to you the already-existing `Table` object if one already exists with the given name. Such as below, we can access the already generated `shopping_carts` table just by naming it:

    shopping_carts = Table("shopping_carts", metadata_obj)

Of course, it’s a good idea to use `autoload_with=engine` with the above table regardless. This is so that the table’s attributes will be loaded if they have not been already. The autoload operation only occurs for the table if it hasn’t already been loaded; once loaded, new calls to `Table` with the same name will not re-issue any reflection queries.

## Overriding Reflected Columns

Individual columns can be overridden with explicit values when reflecting tables; this is handy for specifying custom datatypes, constraints such as primary keys that may not be configured within the database, etc.:

    >>> mytable = Table(
    ...     "mytable",
    ...     metadata_obj,
    ...     Column(
    ...         "id", Integer, primary_key=True
    ...     ),  # override reflected 'id' to have primary key
    ...     Column("mydata", Unicode(50)),  # override reflected 'mydata' to be Unicode
    ...     # additional Column objects which require no change are reflected normally
    ...     autoload_with=some_engine,
    ... )

See also

Working with Custom Types and Reflection - illustrates how the above column override technique applies to the use of custom datatypes with table reflection.

## Reflecting Views

The reflection system can also reflect views. Basic usage is the same as that of a table:

    my_view = Table("some_view", metadata, autoload_with=engine)

Above, `my_view` is a `Table` object with `Column` objects representing the names and types of each column within the view “some_view”.

Usually, it’s desired to have at least a primary key constraint when reflecting a view, if not foreign keys as well. View reflection doesn’t extrapolate these constraints.

Use the “override” technique for this, specifying explicitly those columns which are part of the primary key or have foreign key constraints:

    my_view = Table(
        "some_view",
        metadata,
        Column("view_id", Integer, primary_key=True),
        Column("related_thing", Integer, ForeignKey("othertable.thing_id")),
        autoload_with=engine,
    )

## Reflecting All Tables at Once

The `MetaData` object can also get a listing of tables and reflect the full set. This is achieved by using the `reflect()` method. After calling it, all located tables are present within the `MetaData` object’s dictionary of tables:

    metadata_obj = MetaData()
    metadata_obj.reflect(bind=someengine)
    users_table = metadata_obj.tables["users"]
    addresses_table = metadata_obj.tables["addresses"]

`metadata.reflect()` also provides a handy way to clear or delete all the rows in a database:

    metadata_obj = MetaData()
    metadata_obj.reflect(bind=someengine)
    with someengine.begin() as conn:
        for table in reversed(metadata_obj.sorted_tables):
            conn.execute(table.delete())

## Reflecting Tables from Other Schemas

The section Specifying the Schema Name introduces the concept of table schemas, which are namespaces within a database that contain tables and other objects, and which can be specified explicitly. The “schema” for a `Table` object, as well as for other objects like views, indexes and sequences, can be set up using the `Table.schema` parameter, and also as the default schema for a `MetaData` object using the `MetaData.schema` parameter.

The use of this schema parameter directly affects where the table reflection feature will look when it is asked to reflect objects. For example, given a `MetaData` object configured with a default schema name “project” via its `MetaData.schema` parameter:

    >>> metadata_obj = MetaData(schema="project")

The `MetaData.reflect()` will then utilize that configured `.schema` for reflection:

    >>> # uses `schema` configured in metadata_obj
    >>> metadata_obj.reflect(someengine)

The end result is that `Table` objects from the “project” schema will be reflected, and they will be populated as schema-qualified with that name:

    >>> metadata_obj.tables["project.messages"]
    Table('messages', MetaData(), Column('message_id', INTEGER(), table=<messages>), schema='project')

Similarly, an individual `Table` object that includes the `Table.schema` parameter will also be reflected from that database schema, overriding any default schema that may have been configured on the owning `MetaData` collection:

    >>> messages = Table("messages", metadata_obj, schema="project", autoload_with=someengine)
    >>> messages
    Table('messages', MetaData(), Column('message_id', INTEGER(), table=<messages>), schema='project')

Finally, the `MetaData.reflect()` method itself also allows a `MetaData.reflect.schema` parameter to be passed, so we could also load tables from the “project” schema for a default configured `MetaData` object:

    >>> metadata_obj = MetaData()
    >>> metadata_obj.reflect(someengine, schema="project")

We can call `MetaData.reflect()` any number of times with different `MetaData.schema` arguments (or none at all) to continue populating the `MetaData` object with more objects:

    >>> # add tables from the "customer" schema
    >>> metadata_obj.reflect(someengine, schema="customer")
    >>> # add tables from the default schema
    >>> metadata_obj.reflect(someengine)

### Interaction of Schema-qualified Reflection with the Default Schema

Section Best Practices Summarized

In this section, we discuss SQLAlchemy’s reflection behavior regarding tables that are visible in the “default schema” of a database session, and how these interact with SQLAlchemy directives that include the schema explicitly. As a best practice, ensure the “default” schema for a database is just a single name, and not a list of names; for tables that are part of this “default” schema and can be named without schema qualification in DDL and SQL, leave corresponding `Table.schema` and similar schema parameters set to their default of `None`.

As described at Specifying a Default Schema Name with MetaData, databases that have the concept of schemas usually also include the concept of a “default” schema. The reason for this is naturally that when one refers to table objects without a schema as is common, a schema-capable database will still consider that table to be in a “schema” somewhere. Some databases such as PostgreSQL take this concept further into the notion of a schema search path where multiple schema names can be considered in a particular database session to be “implicit”; referring to a table name that it’s any of those schemas will not require that the schema name be present (while at the same time it’s also perfectly fine if the schema name is present).

Since most relational databases therefore have the concept of a particular table object which can be referenced both in a schema-qualified way, as well as an “implicit” way where no schema is present, this presents a complexity for SQLAlchemy’s reflection feature. Reflecting a table in a schema-qualified manner will always populate its `Table.schema` attribute and additionally affect how this `Table` is organized into the `MetaData.tables` collection, that is, in a schema qualified manner. Conversely, reflecting the same table in a non-schema qualified manner will organize it into the `MetaData.tables` collection without being schema qualified. The end result is that there would be two separate `Table` objects in the single `MetaData` collection representing the same table in the actual database.

To illustrate the ramifications of this issue, consider tables from the “project” schema in the previous example, and suppose also that the “project” schema is the default schema of our database connection, or if using a database such as PostgreSQL suppose the “project” schema is set up in the PostgreSQL `search_path`. This would mean that the database accepts the following two SQL statements as equivalent:

    -- schema qualified
    SELECT message_id FROM project.messages

    -- non-schema qualified
    SELECT message_id FROM messages

This is not a problem as the table can be found in both ways. However in SQLAlchemy, it’s the identity of the `Table` object that determines its semantic role within a SQL statement. Based on the current decisions within SQLAlchemy, this means that if we reflect the same “messages” table in both a schema-qualified as well as a non-schema qualified manner, we get two `Table` objects that will not be treated as semantically equivalent:

    >>> # reflect in non-schema qualified fashion
    >>> messages_table_1 = Table("messages", metadata_obj, autoload_with=someengine)
    >>> # reflect in schema qualified fashion
    >>> messages_table_2 = Table(
    ...     "messages", metadata_obj, schema="project", autoload_with=someengine
    ... )
    >>> # two different objects
    >>> messages_table_1 is messages_table_2
    False
    >>> # stored in two different ways
    >>> metadata.tables["messages"] is messages_table_1
    True
    >>> metadata.tables["project.messages"] is messages_table_2
    True

The above issue becomes more complicated when the tables being reflected contain foreign key references to other tables. Suppose “messages” has a “project_id” column which refers to rows in another schema-local table “projects”, meaning there is a `ForeignKeyConstraint` object that is part of the definition of the “messages” table.

We can find ourselves in a situation where one `MetaData` collection may contain as many as four `Table` objects representing these two database tables, where one or two of the additional tables were generated by the reflection process; this is because when the reflection process encounters a foreign key constraint on a table being reflected, it branches out to reflect that referenced table as well. The decision making it uses to assign the schema to this referenced table is that SQLAlchemy will omit a default schema from the reflected `ForeignKeyConstraint` object if the owning `Table` also omits its schema name and also that these two objects are in the same schema, but will include it if it were not omitted.

The common scenario is when the reflection of a table in a schema qualified fashion then loads a related table that will also be performed in a schema qualified fashion:

    >>> # reflect "messages" in a schema qualified fashion
    >>> messages_table_1 = Table(
    ...     "messages", metadata_obj, schema="project", autoload_with=someengine
    ... )

The above `messages_table_1` will refer to `projects` also in a schema qualified fashion. This “projects” table will be reflected automatically by the fact that “messages” refers to it:

    >>> messages_table_1.c.project_id
    Column('project_id', INTEGER(), ForeignKey('project.projects.project_id'), table=<messages>)

if some other part of the code reflects “projects” in a non-schema qualified fashion, there are now two projects tables that are not the same:

    >>> # reflect "projects" in a non-schema qualified fashion
    >>> projects_table_1 = Table("projects", metadata_obj, autoload_with=someengine)

    >>> # messages does not refer to projects_table_1 above
    >>> messages_table_1.c.project_id.references(projects_table_1.c.project_id)
    False

    >>> # it refers to this one
    >>> projects_table_2 = metadata_obj.tables["project.projects"]
    >>> messages_table_1.c.project_id.references(projects_table_2.c.project_id)
    True

    >>> # they're different, as one non-schema qualified and the other one is
    >>> projects_table_1 is projects_table_2
    False

The above confusion can cause problems within applications that use table reflection to load up application-level `Table` objects, as well as within migration scenarios, in particular such as when using Alembic Migrations to detect new tables and foreign key constraints.

The above behavior can be remedied by sticking to one simple practice:

- Don’t include the `Table.schema` parameter for any `Table` that expects to be located in the default schema of the database.

For PostgreSQL and other databases that support a “search” path for schemas, add the following additional practice:

- Keep the “search path” narrowed down to one schema only, which is the default schema.

See also

Remote-Schema Table Introspection and PostgreSQL search_path - additional details of this behavior as regards the PostgreSQL database.

## Fine Grained Reflection with Inspector

A low level interface which provides a backend-agnostic system of loading lists of schema, table, column, and constraint descriptions from a given database is also available. This is known as the “Inspector”:

    from sqlalchemy import create_engine
    from sqlalchemy import inspect

    engine = create_engine("...")
    insp = inspect(engine)
    print(insp.get_table_names())

Object Name | Description
--- | ---
Inspector | Performs database schema inspection.
ReflectedCheckConstraint | Dictionary representing the reflected elements corresponding to `CheckConstraint`.
ReflectedColumn | Dictionary representing the reflected elements corresponding to a `Column` object.
ReflectedComputed | Represent the reflected elements of a computed column, corresponding to the `Computed` construct.
ReflectedForeignKeyConstraint | Dictionary representing the reflected elements corresponding to `ForeignKeyConstraint`.
ReflectedIdentity | represent the reflected IDENTITY structure of a column, corresponding to the `Identity` construct.
ReflectedIndex | Dictionary representing the reflected elements corresponding to `Index`.
ReflectedPrimaryKeyConstraint | Dictionary representing the reflected elements corresponding to `PrimaryKeyConstraint`.
ReflectedTableComment | Dictionary representing the reflected comment corresponding to the `Table.comment` attribute.
ReflectedUniqueConstraint | Dictionary representing the reflected elements corresponding to `UniqueConstraint`.

class sqlalchemy.engine.reflection.Inspector

  Performs database schema inspection.

  The Inspector acts as a proxy to the reflection methods of the `Dialect`, providing a consistent interface as well as caching support for previously fetched metadata.

  A `Inspector` object is usually created via the `inspect()` function, which may be passed an `Engine` or a `Connection`:

      from sqlalchemy import inspect, create_engine

      engine = create_engine("...")
      insp = inspect(engine)

  Where above, the `Dialect` associated with the engine may opt to return an `Inspector` subclass that provides additional methods specific to the dialect’s target database.

  Members

  __init__(), bind, clear_cache(), default_schema_name, dialect, engine, from_engine(), get_check_constraints(), get_columns(), get_foreign_keys(), get_indexes(), get_materialized_view_names(), get_multi_check_constraints(), get_multi_columns(), get_multi_foreign_keys(), get_multi_indexes(), get_multi_pk_constraint(), get_multi_table_comment(), get_multi_table_options(), get_multi_unique_constraints(), get_pk_constraint(), get_schema_names(), get_sequence_names(), get_sorted_table_and_fkc_names(), get_table_comment(), get_table_names(), get_table_options(), get_temp_table_names(), get_temp_view_names(), get_unique_constraints(), get_view_definition(), get_view_names(), has_index(), has_schema(), has_sequence(), has_table(), info_cache, reflect_table(), sort_tables_on_foreign_key_dependency()

  Class signature

  class `sqlalchemy.engine.reflection.Inspector` (`sqlalchemy.inspection.Inspectable`)

  method `sqlalchemy.engine.reflection.Inspector.` __init__(bind: Engine | Connection)

    Initialize a new `Inspector`.

    Deprecated since version 1.4: The __init__() method on `Inspector` is deprecated and will be removed in a future release. Please use the `inspect()` function on an `Engine` or `Connection` in order to acquire an `Inspector`.

    Parameters:

      bind – a `Connection`, which is typically an instance of `Engine` or `Connection`.

    For a dialect-specific instance of `Inspector`, see `Inspector.from_engine()`

  attribute `sqlalchemy.engine.reflection.Inspector.` bind: Engine | Connection
  method `sqlalchemy.engine.reflection.Inspector.` clear_cache() → None

    reset the cache for this `Inspector`.

    Inspection methods that have data cached will emit SQL queries when next called to get new data.

    New in version 2.0.

  attribute `sqlalchemy.engine.reflection.Inspector.` default_schema_name

    Return the default schema name presented by the dialect for the current engine’s database user.

    E.g. this is typically `public` for PostgreSQL and `dbo` for SQL Server.

  attribute `sqlalchemy.engine.reflection.Inspector.` dialect: Dialect
  attribute `sqlalchemy.engine.reflection.Inspector.` engine: Engine
  classmethod `sqlalchemy.engine.reflection.Inspector.` from_engine(bind: Engine) → Inspector

    Construct a new dialect-specific Inspector object from the given engine or connection.

    Deprecated since version 1.4: The from_engine() method on `Inspector` is deprecated and will be removed in a future release. Please use the `inspect()` function on an `Engine` or `Connection` in order to acquire an `Inspector`.

    Parameters:

      bind – a `Connection` or `Engine`.

    This method differs from direct a direct constructor call of `Inspector` in that the `Dialect` is given a chance to provide a dialect-specific `Inspector` instance, which may provide additional methods.

    See the example at `Inspector`.

  method `sqlalchemy.engine.reflection.Inspector.` get_check_constraints(table_name: str, schema: str | None = None, **kw: Any) → List[ReflectedCheckConstraint]

    Return information about check constraints in `table_name`.

    Given a string `table_name` and an optional string schema, return check constraint information as a list of `ReflectedCheckConstraint`.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a list of dictionaries, each representing the definition of a check constraints.

    See also

    `Inspector.get_multi_check_constraints()`

  method `sqlalchemy.engine.reflection.Inspector.` get_columns(table_name: str, schema: str | None = None, **kw: Any) → List[ReflectedColumn]

    Return information about columns in `table_name`.

    Given a string `table_name` and an optional string `schema`, return column information as a list of `ReflectedColumn`.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      list of dictionaries, each representing the definition of a database column.

    See also

    `Inspector.get_multi_columns()`.

  method `sqlalchemy.engine.reflection.Inspector.` get_foreign_keys(table_name: str, schema: str | None = None, **kw: Any) → List[ReflectedForeignKeyConstraint]

    Return information about foreign_keys in `table_name`.

    Given a string `table_name`, and an optional string schema, return foreign key information as a list of `ReflectedForeignKeyConstraint`.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a list of dictionaries, each representing the a foreign key definition.

    See also

    `Inspector.get_multi_foreign_keys()`

  method `sqlalchemy.engine.reflection.Inspector.` get_indexes(table_name: str, schema: str | None = None, **kw: Any) → List[ReflectedIndex]

    Return information about indexes in `table_name`.

    Given a string `table_name` and an optional string schema, return index information as a list of `ReflectedIndex`.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a list of dictionaries, each representing the definition of an index.

    See also

    `Inspector.get_multi_indexes()`

  method `sqlalchemy.engine.reflection.Inspector.` get_materialized_view_names(schema: str | None = None, **kw: Any) → List[str]

    Return all materialized view names in schema.

    Parameters:

      - schema – Optional, retrieve names from a non-default schema. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    New in version 2.0.

    See also

    `Inspector.get_view_names()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_check_constraints(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, List[ReflectedCheckConstraint]]

    Return information about check constraints in all tables in the given schema.

    The tables can be filtered by passing the names to use to `filter_names`.

    For each table the value is a list of `ReflectedCheckConstraint`.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if constraints of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are list of dictionaries, each representing the definition of a check constraints. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_check_constraints()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_columns(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, List[ReflectedColumn]]

    Return information about columns in all objects in the given schema.

    The objects can be filtered by passing the names to use to `filter_names`.

    For each table the value is a list of `ReflectedColumn`.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if columns of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are list of dictionaries, each representing the definition of a database column. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_columns()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_foreign_keys(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, List[ReflectedForeignKeyConstraint]]

    Return information about foreign_keys in all tables in the given schema.

    The tables can be filtered by passing the names to use to `filter_names`.

    For each table the value is a list of `ReflectedForeignKeyConstraint`.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if foreign keys of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are list of dictionaries, each representing a foreign key definition. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_foreign_keys()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_indexes(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, List[ReflectedIndex]]

    Return information about indexes in in all objects in the given schema.

    The objects can be filtered by passing the names to use to `filter_names`.

    For each table the value is a list of `ReflectedIndex`.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if indexes of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are list of dictionaries, each representing the definition of an index. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_indexes()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_pk_constraint(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, ReflectedPrimaryKeyConstraint]

    Return information about primary key constraints in all tables in the given schema.

    The tables can be filtered by passing the names to use to `filter_names`.

    For each table the value is a `ReflectedPrimaryKeyConstraint`.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if primary keys of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are dictionaries, each representing the definition of a primary key constraint. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_pk_constraint()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_table_comment(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, ReflectedTableComment]

    Return information about the table comment in all objects in the given schema.

    The objects can be filtered by passing the names to use to `filter_names`.

    For each table the value is a `ReflectedTableComment`.

    Raises `NotImplementedError` for a dialect that does not support comments.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if comments of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are dictionaries, representing the table comments. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_table_comment()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_table_options(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, Dict[str, Any]]

    Return a dictionary of options specified when the tables in the given schema were created.

    The tables can be filtered by passing the names to use to `filter_names`.

    This currently includes some options that apply to MySQL and Oracle tables.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if options of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are dictionaries with the table options. The returned keys in each dict depend on the dialect in use. Each one is prefixed with the dialect name. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_table_options()`

  method `sqlalchemy.engine.reflection.Inspector.` get_multi_unique_constraints(schema: str | None = None, filter_names: Sequence[str] | None = None, kind: ObjectKind = ObjectKind.TABLE, scope: ObjectScope = ObjectScope.DEFAULT, **kw: Any) → Dict[TableKey, List[ReflectedUniqueConstraint]]

    Return information about unique constraints in all tables in the given schema.

    The tables can be filtered by passing the names to use to `filter_names`.

    For each table the value is a list of `ReflectedUniqueConstraint`.

    Parameters:

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - filter_names – optionally return information only for the objects listed here.

      - kind – a `ObjectKind` that specifies the type of objects to reflect. Defaults to `ObjectKind.TABLE`.

      - scope – a `ObjectScope` that specifies if constraints of default, temporary or any tables should be reflected. Defaults to `ObjectScope.DEFAULT`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary where the keys are two-tuple schema,table-name and the values are list of dictionaries, each representing the definition of an unique constraint. The schema is `None` if no schema is provided.

    New in version 2.0.

    See also

    `Inspector.get_unique_constraints()`

  method `sqlalchemy.engine.reflection.Inspector.` get_pk_constraint(table_name: str, schema: str | None = None, **kw: Any) → ReflectedPrimaryKeyConstraint

    Return information about primary key constraint in `table_name`.

    Given a string `table_name`, and an optional string schema, return primary key information as a `ReflectedPrimaryKeyConstraint`.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary representing the definition of a primary key constraint.

    See also

    `Inspector.get_multi_pk_constraint()`

  method `sqlalchemy.engine.reflection.Inspector.` get_schema_names(**kw: Any) → List[str]

    Return all schema names.

    Parameters:

      **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

  method `sqlalchemy.engine.reflection.Inspector.` get_sequence_names(schema: str | None = None, **kw: Any) → List[str]

    Return all sequence names in schema.

    Parameters:

      - schema – Optional, retrieve names from a non-default schema. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

  method `sqlalchemy.engine.reflection.Inspector.` get_sorted_table_and_fkc_names(schema: str | None = None, **kw: Any) → List[Tuple[str | None, List[Tuple[str, str | None]]]]

    Return dependency-sorted table and foreign key constraint names in referred to within a particular schema.

    This will yield 2-tuples of `(tablename, [(tname, fkname), (tname, fkname), ...])` consisting of table names in CREATE order grouped with the foreign key constraint names that are not detected as belonging to a cycle. The final element will be `(None, [(tname, fkname), (tname, fkname), ..])` which will consist of remaining foreign key constraint names that would require a separate CREATE step after-the-fact, based on dependencies between tables.

    Parameters:

      - schema – schema name to query, if not the default schema.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    See also

    `Inspector.get_table_names()`

    `sort_tables_and_constraints()` - similar method which works with an already-given `MetaData`.

  method `sqlalchemy.engine.reflection.Inspector.` get_table_comment(table_name: str, schema: str | None = None, **kw: Any) → ReflectedTableComment

    Return information about the table comment for `table_name`.

    Given a string `table_name` and an optional string `schema`, return table comment information as a `ReflectedTableComment`.

    Raises `NotImplementedError` for a dialect that does not support comments.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dictionary, with the table comment.

    New in version 1.2.

    See also

    `Inspector.get_multi_table_comment()`

  method `sqlalchemy.engine.reflection.Inspector.` get_table_names(schema: str | None = None, **kw: Any) → List[str]

    Return all table names within a particular schema.

    The names are expected to be real tables only, not views. Views are instead returned using the `Inspector.get_view_names()` and/or `Inspector.get_materialized_view_names()` methods.

    Parameters:

      - schema – Schema name. If `schema` is left at `None`, the database’s default schema is used, else the named schema is searched. If the database does not support named schemas, behavior is undefined if `schema` is not passed as `None`. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    See also

    `Inspector.get_sorted_table_and_fkc_names()`

    `MetaData.sorted_tables`

  method `sqlalchemy.engine.reflection.Inspector.` get_table_options(table_name: str, schema: str | None = None, **kw: Any) → Dict[str, Any]

    Return a dictionary of options specified when the table of the given name was created.

    This currently includes some options that apply to MySQL and Oracle Database tables.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a dict with the table options. The returned keys depend on the dialect in use. Each one is prefixed with the dialect name.

    See also

    `Inspector.get_multi_table_options()`

  method `sqlalchemy.engine.reflection.Inspector.` get_temp_table_names(**kw: Any) → List[str]

    Return a list of temporary table names for the current bind.

    This method is unsupported by most dialects; currently only Oracle Database, PostgreSQL and SQLite implements it.

    Parameters:

      **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

  method `sqlalchemy.engine.reflection.Inspector.` get_temp_view_names(**kw: Any) → List[str]

    Return a list of temporary view names for the current bind.

    This method is unsupported by most dialects; currently only PostgreSQL and SQLite implements it.

    Parameters:

      **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

  method `sqlalchemy.engine.reflection.Inspector.` get_unique_constraints(table_name: str, schema: str | None = None, **kw: Any) → List[ReflectedUniqueConstraint]

    Return information about unique constraints in `table_name`.

    Given a string `table_name` and an optional string schema, return unique constraint information as a list of `ReflectedUniqueConstraint`.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Returns:

      a list of dictionaries, each representing the definition of an unique constraint.

    See also

    `Inspector.get_multi_unique_constraints()`

  method `sqlalchemy.engine.reflection.Inspector.` get_view_definition(view_name: str, schema: str | None = None, **kw: Any) → str

    Return definition for the plain or materialized view called `view_name`.

    Parameters:

      - view_name – Name of the view.

      - schema – Optional, retrieve names from a non-default schema. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

  method `sqlalchemy.engine.reflection.Inspector.` get_view_names(schema: str | None = None, **kw: Any) → List[str]

    Return all non-materialized view names in schema.

    Parameters:

      - schema – Optional, retrieve names from a non-default schema. For special quoting, use `quoted_name`.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    Changed in version 2.0: For those dialects that previously included the names of materialized views in this list (currently PostgreSQL), this method no longer returns the names of materialized views. the `Inspector.get_materialized_view_names()` method should be used instead.

    See also

    `Inspector.get_materialized_view_names()`

  method `sqlalchemy.engine.reflection.Inspector.` has_index(table_name: str, index_name: str, schema: str | None = None, **kw: Any) → bool

    Check the existence of a particular index name in the database.

    Parameters:

      - table_name – the name of the table the index belongs to

      - index_name – the name of the index to check

      - schema – schema name to query, if not the default schema.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    New in version 2.0.

  method `sqlalchemy.engine.reflection.Inspector.` has_schema(schema_name: str, **kw: Any) → bool

    Return True if the backend has a schema with the given name.

    Parameters:

      - schema_name – name of the schema to check

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    New in version 2.0.

  method `sqlalchemy.engine.reflection.Inspector.` has_sequence(sequence_name: str, schema: str | None = None, **kw: Any) → bool

    Return True if the backend has a sequence with the given name.

    Parameters:

      - sequence_name – name of the sequence to check

      - schema – schema name to query, if not the default schema.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    New in version 1.4.

  method `sqlalchemy.engine.reflection.Inspector.` has_table(table_name: str, schema: str | None = None, **kw: Any) → bool

    Return True if the backend has a table, view, or temporary table of the given name.

    Parameters:

      - table_name – name of the table to check

      - schema – schema name to query, if not the default schema.

      - **kw – Additional keyword argument to pass to the dialect specific implementation. See the documentation of the dialect in use for more information.

    New in version 1.4: - the `Inspector.has_table()` method replaces the `Engine.has_table()` method.

    Changed in version 2.0::: `Inspector.has_table()` now formally supports checking for additional table-like objects:

    - any type of views (plain or materialized)

    - temporary tables of any kind

    Previously, these two checks were not formally specified and different dialects would vary in their behavior. The dialect testing suite now includes tests for all of these object types and should be supported by all SQLAlchemy-included dialects. Support among third party dialects may be lagging, however.

  attribute `sqlalchemy.engine.reflection.Inspector.` info_cache: Dict[Any, Any]
  method `sqlalchemy.engine.reflection.Inspector.` reflect_table(table: Table, include_columns: Collection[str] | None, exclude_columns: Collection[str] = (), resolve_fks: bool = True, _extend_on: Set[Table] | None = None, _reflect_info: _ReflectionInfo | None = None) → None

    Given a `Table` object, load its internal constructs based on introspection.

    This is the underlying method used by most dialects to produce table reflection. Direct usage is like:

        from sqlalchemy import create_engine, MetaData, Table
        from sqlalchemy import inspect

        engine = create_engine("...")
        meta = MetaData()
        user_table = Table("user", meta)
        insp = inspect(engine)
        insp.reflect_table(user_table, None)

    Changed in version 1.4: Renamed from `reflecttable` to `reflect_table`

    Parameters:

      - table – a `Table` instance.

      - include_columns – a list of string column names to include in the reflection process. If `None`, all columns are reflected.

  method `sqlalchemy.engine.reflection.Inspector.` sort_tables_on_foreign_key_dependency(consider_schemas: Collection[str | None] = (None,), **kw: Any) → List[Tuple[Tuple[str | None, str] | None, List[Tuple[Tuple[str | None, str], str | None]]]]

    Return dependency-sorted table and foreign key constraint names referred to within multiple schemas.

    This method may be compared to `Inspector.get_sorted_table_and_fkc_names()`, which works on one schema at a time; here, the method is a generalization that will consider multiple schemas at once including that it will resolve for cross-schema foreign keys.

    New in version 2.0.

class sqlalchemy.engine.interfaces.ReflectedColumn

  Dictionary representing the reflected elements corresponding to a `Column` object.

  The `ReflectedColumn` structure is returned by the `get_columns` method.

  Members

  autoincrement, comment, computed, default, dialect_options, identity, name, nullable, type

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedColumn` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` autoincrement: NotRequired[bool]

    database-dependent autoincrement flag.

    This flag indicates if the column has a database-side “autoincrement” flag of some kind. Within SQLAlchemy, other kinds of columns may also act as an “autoincrement” column without necessarily having such a flag on them.

    See `Column.autoincrement` for more background on “autoincrement”.

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` comment: NotRequired[str | None]

    comment for the column, if present. Only some dialects return this key

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` computed: NotRequired[ReflectedComputed]

    indicates that this column is computed by the database. Only some dialects return this key.

    New in version 1.3.16: - added support for computed reflection.

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` default: str | None

    column default expression as a SQL string

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` dialect_options: NotRequired[Dict[str, Any]]

    Additional dialect-specific options detected for this reflected object

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` identity: NotRequired[ReflectedIdentity]

    indicates this column is an IDENTITY column. Only some dialects return this key.

    New in version 1.4: - added support for identity column reflection.

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` name: str

    column name

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` nullable: bool

    boolean flag if the column is NULL or NOT NULL

  attribute `sqlalchemy.engine.interfaces.ReflectedColumn.` type: TypeEngine[Any]

    column type represented as a `TypeEngine` instance.

class sqlalchemy.engine.interfaces.ReflectedComputed

  Represent the reflected elements of a computed column, corresponding to the `Computed` construct.

  The `ReflectedComputed` structure is part of the `ReflectedColumn` structure, which is returned by the `Inspector.get_columns()` method.

  Members

  persisted, sqltext

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedComputed` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedComputed.` persisted: bool

    indicates if the value is stored in the table or computed on demand

  attribute `sqlalchemy.engine.interfaces.ReflectedComputed.` sqltext: str

    the expression used to generate this column returned as a string SQL expression

class sqlalchemy.engine.interfaces.ReflectedCheckConstraint

  Dictionary representing the reflected elements corresponding to `CheckConstraint`.

  The `ReflectedCheckConstraint` structure is returned by the `Inspector.get_check_constraints()` method.

  Members

  dialect_options, sqltext

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedCheckConstraint` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedCheckConstraint.` dialect_options: Dict[str, Any]

    Additional dialect-specific options detected for this check constraint

    New in version 1.3.8.

  attribute `sqlalchemy.engine.interfaces.ReflectedCheckConstraint.` sqltext: str

    the check constraint’s SQL expression

class sqlalchemy.engine.interfaces.ReflectedForeignKeyConstraint

  Dictionary representing the reflected elements corresponding to `ForeignKeyConstraint`.

  The `ReflectedForeignKeyConstraint` structure is returned by the `Inspector.get_foreign_keys()` method.

  Members

  constrained_columns, options, referred_columns, referred_schema, referred_table

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedForeignKeyConstraint` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedForeignKeyConstraint.` constrained_columns: List[str]

    local column names which comprise the foreign key

  attribute `sqlalchemy.engine.interfaces.ReflectedForeignKeyConstraint.` options: Dict[str, Any]

    Additional options detected for this foreign key constraint

  attribute `sqlalchemy.engine.interfaces.ReflectedForeignKeyConstraint.` referred_columns: List[str]

    referred column names that correspond to `constrained_columns`

  attribute `sqlalchemy.engine.interfaces.ReflectedForeignKeyConstraint.` referred_schema: str | None

    schema name of the table being referred

  attribute `sqlalchemy.engine.interfaces.ReflectedForeignKeyConstraint.` referred_table: str

    name of the table being referred

class sqlalchemy.engine.interfaces.ReflectedIdentity

  represent the reflected IDENTITY structure of a column, corresponding to the `Identity` construct.

  The `ReflectedIdentity` structure is part of the `ReflectedColumn` structure, which is returned by the `Inspector.get_columns()` method.

  Members

  always, cache, cycle, increment, maxvalue, minvalue, nomaxvalue, nominvalue, on_null, order, start

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedIdentity` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` always: bool

    type of identity column

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` cache: int | None

    number of future values in the sequence which are calculated in advance.

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` cycle: bool

    allows the sequence to wrap around when the maxvalue or minvalue has been reached.

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` increment: int

    increment value of the sequence

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` maxvalue: int

    the maximum value of the sequence.

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` minvalue: int

    the minimum value of the sequence.

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` nomaxvalue: bool

    no maximum value of the sequence.

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` nominvalue: bool

    no minimum value of the sequence.

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` on_null: bool

    indicates ON NULL

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` order: bool

    if true, renders the ORDER keyword.

  attribute `sqlalchemy.engine.interfaces.ReflectedIdentity.` start: int

    starting index of the sequence

class sqlalchemy.engine.interfaces.ReflectedIndex

  Dictionary representing the reflected elements corresponding to `Index`.

  The `ReflectedIndex` structure is returned by the `Inspector.get_indexes()` method.

  Members

  column_names, column_sorting, dialect_options, duplicates_constraint, expressions, include_columns, name, unique

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedIndex` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` column_names: List[str | None]

    column names which the index references. An element of this list is `None` if it’s an expression and is returned in the `expressions` list.

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` column_sorting: Dict[str, Tuple[str]]

    optional dict mapping column names or expressions to tuple of sort keywords, which may include `asc`, `desc`, `nulls_first`, `nulls_last`.

    New in version 1.3.5.

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` dialect_options: Dict[str, Any]

    Additional dialect-specific options detected for this index

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` duplicates_constraint: str | None

    Indicates if this index mirrors a constraint with this name

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` expressions: List[str]

    Expressions that compose the index. This list, when present, contains both plain column names (that are also in `column_names`) and expressions (that are `None` in `column_names`).

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` include_columns: List[str]

    columns to include in the INCLUDE clause for supporting databases.

    Deprecated since version 2.0: Legacy value, will be replaced with `index_dict["dialect_options"]["<dialect name>_include"]`

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` name: str | None

    index name

  attribute `sqlalchemy.engine.interfaces.ReflectedIndex.` unique: bool

    whether or not the index has a unique flag

class sqlalchemy.engine.interfaces.ReflectedPrimaryKeyConstraint

  Dictionary representing the reflected elements corresponding to `PrimaryKeyConstraint`.

  The `ReflectedPrimaryKeyConstraint` structure is returned by the `Inspector.get_pk_constraint()` method.

  Members

  constrained_columns, dialect_options

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedPrimaryKeyConstraint` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedPrimaryKeyConstraint.` constrained_columns: List[str]

    column names which comprise the primary key

  attribute `sqlalchemy.engine.interfaces.ReflectedPrimaryKeyConstraint.` dialect_options: Dict[str, Any]

    Additional dialect-specific options detected for this primary key

class sqlalchemy.engine.interfaces.ReflectedUniqueConstraint

  Dictionary representing the reflected elements corresponding to `UniqueConstraint`.

  The `ReflectedUniqueConstraint` structure is returned by the `Inspector.get_unique_constraints()` method.

  Members

  column_names, dialect_options, duplicates_index

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedUniqueConstraint` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedUniqueConstraint.` column_names: List[str]

    column names which comprise the unique constraint

  attribute `sqlalchemy.engine.interfaces.ReflectedUniqueConstraint.` dialect_options: Dict[str, Any]

    Additional dialect-specific options detected for this unique constraint

  attribute `sqlalchemy.engine.interfaces.ReflectedUniqueConstraint.` duplicates_index: str | None

    Indicates if this unique constraint duplicates an index with this name

class sqlalchemy.engine.interfaces.ReflectedTableComment

  Dictionary representing the reflected comment corresponding to the `Table.comment` attribute.

  The `ReflectedTableComment` structure is returned by the `Inspector.get_table_comment()` method.

  Members

  text

  Class signature

  class `sqlalchemy.engine.interfaces.ReflectedTableComment` (`builtins.dict`)

  attribute `sqlalchemy.engine.interfaces.ReflectedTableComment.` text: str | None

    text of the comment

## Reflecting with Database-Agnostic Types

When the columns of a table are reflected, using either the `Table.autoload_with` parameter of `Table` or the `Inspector.get_columns()` method of `Inspector`, the datatypes will be as specific as possible to the target database. This means that if an “integer” datatype is reflected from a MySQL database, the type will be represented by the `sqlalchemy.dialects.mysql.INTEGER` class, which includes MySQL-specific attributes such as “display_width”. Or on PostgreSQL, a PostgreSQL-specific datatype such as `sqlalchemy.dialects.postgresql.INTERVAL` or `sqlalchemy.dialects.postgresql.ENUM` may be returned.

There is a use case for reflection which is that a given `Table` is to be transferred to a different vendor database. To suit this use case, there is a technique by which these vendor-specific datatypes can be converted on the fly to be instance of SQLAlchemy backend-agnostic datatypes, for the examples above types such as `Integer`, `Interval` and `Enum`. This may be achieved by intercepting the column reflection using the `DDLEvents.column_reflect()` event in conjunction with the `TypeEngine.as_generic()` method.

Given a table in MySQL (chosen because MySQL has a lot of vendor-specific datatypes and options):

    CREATE TABLE IF NOT EXISTS my_table (
        id INTEGER PRIMARY KEY AUTO_INCREMENT,
        data1 VARCHAR(50) CHARACTER SET latin1,
        data2 MEDIUMINT(4),
        data3 TINYINT(2)
    )

The above table includes MySQL-only integer types `MEDIUMINT` and `TINYINT` as well as a `VARCHAR` that includes the MySQL-only `CHARACTER SET` option. If we reflect this table normally, it produces a `Table` object that will contain those MySQL-specific datatypes and options:

    >>> from sqlalchemy import MetaData, Table, create_engine
    >>> mysql_engine = create_engine("mysql+mysqldb://scott:tiger@localhost/test")
    >>> metadata_obj = MetaData()
    >>> my_mysql_table = Table("my_table", metadata_obj, autoload_with=mysql_engine)

The above example reflects the above table schema into a new `Table` object. We can then, for demonstration purposes, print out the MySQL-specific “CREATE TABLE” statement using the `CreateTable` construct:

    >>> from sqlalchemy.schema import CreateTable
    >>> print(CreateTable(my_mysql_table).compile(mysql_engine))
    CREATE TABLE my_table (
    id INTEGER(11) NOT NULL AUTO_INCREMENT,
    data1 VARCHAR(50) CHARACTER SET latin1,
    data2 MEDIUMINT(4),
    data3 TINYINT(2),
    PRIMARY KEY (id)
    )ENGINE=InnoDB DEFAULT CHARSET=utf8mb4

Above, the MySQL-specific datatypes and options were maintained. If we wanted a `Table` that we could instead transfer cleanly to another database vendor, replacing the special datatypes `sqlalchemy.dialects.mysql.MEDIUMINT` and `sqlalchemy.dialects.mysql.TINYINT` with `Integer`, we can choose instead to “genericize” the datatypes on this table, or otherwise change them in any way we’d like, by establishing a handler using the `DDLEvents.column_reflect()` event. The custom handler will make use of the `TypeEngine.as_generic()` method to convert the above MySQL-specific type objects into generic ones, by replacing the `"type"` entry within the column dictionary entry that is passed to the event handler. The format of this dictionary is described at `Inspector.get_columns()`:

    >>> from sqlalchemy import event
    >>> metadata_obj = MetaData()

    >>> @event.listens_for(metadata_obj, "column_reflect")
    ... def genericize_datatypes(inspector, tablename, column_dict):
    ...     column_dict["type"] = column_dict["type"].as_generic()

    >>> my_generic_table = Table("my_table", metadata_obj, autoload_with=mysql_engine)

We now get a new `Table` that is generic and uses `Integer` for those datatypes. We can now emit a “CREATE TABLE” statement for example on a PostgreSQL database:

    >>> pg_engine = create_engine("postgresql+psycopg2://scott:tiger@localhost/test", echo=True)
    >>> my_generic_table.create(pg_engine)
    CREATE TABLE my_table (
        id SERIAL NOT NULL,
        data1 VARCHAR(50),
        data2 INTEGER,
        data3 INTEGER,
        PRIMARY KEY (id)
    )

Noting above also that SQLAlchemy will usually make a decent guess for other behaviors, such as that the MySQL `AUTO_INCREMENT` directive is represented in PostgreSQL most closely using the `SERIAL` auto-incrementing datatype.

New in version 1.4: Added the `TypeEngine.as_generic()` method and additionally improved the use of the `DDLEvents.column_reflect()` event such that it may be applied to a `MetaData` object for convenience.

## Limitations of Reflection

It’s important to note that the reflection process recreates `Table` metadata using only information which is represented in the relational database. This process by definition cannot restore aspects of a schema that aren’t actually stored in the database. State which is not available from reflection includes but is not limited to:

- Client side defaults, either Python functions or SQL expressions defined using the `default` keyword of `Column` (note this is separate from `server_default`, which specifically is what’s available via reflection).

- Column information, e.g. data that might have been placed into the `Column.info` dictionary

- The value of the `.quote` setting for `Column` or `Table`

- The association of a particular `Sequence` with a given `Column`

The relational database also in many cases reports on table metadata in a different format than what was specified in SQLAlchemy. The `Table` objects returned from reflection cannot be always relied upon to produce the identical DDL as the original Python-defined `Table` objects. Areas where this occurs includes server defaults, column-associated sequences and various idiosyncrasies regarding constraints and datatypes. Server side defaults may be returned with cast directives (typically PostgreSQL will include a `::<type>` cast) or different quoting patterns than originally specified.

Another category of limitation includes schema structures for which reflection is only partially or not yet defined. Recent improvements to reflection allow things like views, indexes and foreign key options to be reflected. As of this writing, structures like CHECK constraints, table comments, and triggers are not reflected.