Create a new ReadConcern

# MongoDB\Driver\ReadConcern::__construct

(mongodb >=1.0.0)

MongoDB\Driver\ReadConcern::__construct — Create a new ReadConcern

### 说明

final public function MongoDB\Driver\ReadConcern::__construct(?string `$level` = `null`)

Constructs a new MongoDB\Driver\ReadConcern, which is an immutable value object.

### 参数

`level`
  The » read concern level. You may use, but are not limited to, one of the class constants.

### 错误／异常

- Throws MongoDB\Driver\Exception\InvalidArgumentException on argument parsing errors.

### 示例

示例 #1 MongoDB\Driver\ReadConcern::__construct() example

    <?php

    /* Unspecified read isolation level (uses the server's default behavior) */
    $rc = new MongoDB\Driver\ReadConcern();

    /* Request read isolation from a single replica set node */
    $rc = new MongoDB\Driver\ReadConcern(MongoDB\Driver\ReadConcern::LOCAL);

    /* Request read isolation from a majority of the replica set nodes */
    $rc = new MongoDB\Driver\ReadConcern(MongoDB\Driver\ReadConcern::MAJORITY);

    ?>

### 参见

- » Read Concern reference

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