如果key为空，为什么post post meta参数不起作用

Question

I wanted to get all the post meta using this code:

$metas = get_post_meta( $post_id, '', true );

The code above will output an array that looks something like:

array(
    'sample_key1' => array(
        [0] => 'value1'
    ),
    'sample_key2' => array(
        [0] => 'value2'
    ),
    'sample_key3' => array(
        [0] => 'value3'
    )
)

Rather than

array(
    'sample_key1' => 'value1',
    'sample_key2' => 'value2',
    'sample_key3' => 'value3'
)

hence the $single param is true.

It will work when you put a specific key like:

$meta1 = get_post_meta( $post_id, 'sample_meta1' );

will output something like:

array(
    [0] => 'value1'
)

and when the $single param is true:

$meta1 = get_post_meta( $post_id, 'sample_meta1', true );

will output something like:

'value1'

I would appreciate any answer I can get.

Answer 1

The get_post_meta() function using get_metadata() function. And according to documentation get_metadata() the 3rd bool parameter only work if the meta_key exists.

If true, return only the first value of the specified meta_key. This parameter has no effect if meta_key is not specified.

Hope this helped you to understand.