Checks if this is the default read concern

# MongoDB\Driver\ReadConcern::isDefault

(mongodb >=1.3.0)

MongoDB\Driver\ReadConcern::isDefault — Checks if this is the default read concern

### 説明

final public MongoDB\Driver\ReadConcern::isDefault ( void ) : bool

Returns whether this is the default read concern (i.e. no options are specified). This method is primarily intended to be used in conjunction with MongoDB\Driver\Manager::getReadConcern() to determine whether the Manager has been constructed without any read concern options.

The driver will not include a default read concern in its read operations (e.g. MongoDB\Driver\Manager::executeQuery()) in order order to allow the server to apply its own default. Libraries that access the Manager's read concern to include it in their own read commands should use this method to ensure that default read concerns are left unset.

### パラメータ

この関数にはパラメータはありません。

### 返り値

Returns `TRUE` if this is the default read concern and `FALSE` otherwise.

### エラー / 例外

- 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。

### 例

例1 MongoDB\Driver\ReadConcern::isDefault() example

`<?php
$rc = new MongoDB\Driver\ReadConcern(null);
var_dump($rc->isDefault());
$rc = new MongoDB\Driver\ReadConcern(MongoDB\Driver\ReadConcern::MAJORITY);
var_dump($rc->isDefault());
$manager = new MongoDB\Driver\Manager('mongodb://127.0.0.1/?readConcernLevel=majority');
$rc = $manager->getReadConcern();
var_dump($rc->isDefault());
$manager = new MongoDB\Driver\Manager('mongodb://127.0.0.1/');
$rc = $manager->getReadConcern();
var_dump($rc->isDefault());
?>`

上の例の出力は以下となります。

    bool(true)
    bool(false)
    bool(false)
    bool(true)

### 参考

- MongoDB\Driver\Manager::getReadConcern() - Return the ReadConcern for the Manager
- » Read Concern reference