# MongoDB\BSON\Iterator::key

(mongodb >=1.16.0)

MongoDB\BSON\Iterator::key — Returns the key of the current element

### 说明

public MongoDB\BSON\Iterator::key(): string|int

### 参数

此函数没有参数。

### 返回值

Returns the key of the current element. When iterating a BSON document, the key will always be a string. When iterating a BSON array, the key will be an int.

### 错误／异常

- Throws MongoDB\Driver\Exception\InvalidArgumentException on argument parsing errors.
- Throws MongoDB\Driver\Exception\LogicException if the iterator is not valid.

### 参见

- Iterator::key() - 返回当前元素的键

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