Execute a database command that reads on this server

# MongoDB\Driver\Server::executeReadCommand

(mongodb >=1.4.0)

MongoDB\Driver\Server::executeReadCommand — Execute a database command that reads on this server

### 説明

final public MongoDB\Driver\Server::executeReadCommand ( string `$db` , MongoDB\Driver\Command `$command` [, array `$options` = array() ] ) : MongoDB\Driver\Cursor

Executes the command on this server.

This method will apply logic that is specific to commands that read (e.g. » count) and take the MongoDB server version into account. The "readConcern" option will default to the corresponding value from the MongoDB Connection URI.

> 注意: The "readPreference" option does not control the server to which the driver issues the operation; it will always be executed on this server object. Instead, it may be used when issuing the operation to a secondary (from a replica set connection, not standalone) or mongos node to ensure that the driver sets the wire protocol accordingly or adds the read preference to the operation, respectively.

### パラメータ

`db` (string)

  コマンドを実行するデータベースの名前。

`command` (MongoDB\Driver\Command)

  実行するコマンド。

`options`

  options
  Option | Type | Description
  --- | --- | ---
  readConcern | MongoDB\Driver\ReadConcern | A read concern to apply to the operation. This option is available in MongoDB 3.2+ and will result in an exception at execution time if specified for an older server version.
  readPreference | MongoDB\Driver\ReadPreference | A read preference to use for selecting a server for the operation.
  session | MongoDB\Driver\Session | A session to associate with the operation.

  警告

  If you are using a "session" which has a transaction in progress, you cannot specify a "readConcern" or "writeConcern" option. This will result in an MongoDB\Driver\Exception\InvalidArgumentException being thrown. Instead, you should set these two options when you create the transaction with MongoDB\Driver\Session::startTransaction().

### 返り値

成功した場合に MongoDB\Driver\Cursor を返します。

### エラー / 例外

- Throws MongoDB\Driver\Exception\InvalidArgumentException if the "session" option is used with an associated transaction in combination with a "readConcern" or "writeConcern" option.
- 引数のパースに失敗した場合に MongoDB\Driver\Exception\InvalidArgumentException をスローします。
- サーバーへの接続が認証以外の理由で失敗した場合に MongoDB\Driver\Exception\ConnectionException をスローします。
- 認証が必要な場面で認証に失敗した場合に MongoDB\Driver\Exception\AuthenticationException をスローします。
- Throws MongoDB\Driver\Exception\RuntimeException on other errors (e.g. invalid command).

### 参考

- MongoDB\Driver\Command
- MongoDB\Driver\Cursor
- MongoDB\Driver\Server::executeCommand() - Execute a database command on this server
- MongoDB\Driver\Server::executeReadWriteCommand() - Execute a database command that reads and writes on this server
- MongoDB\Driver\Server::executeWriteCommand() - Execute a database command that writes on this server
- MongoDB\Driver\Manager::executeReadCommand() - Execute a database command that reads