Why is get_post_meta returning an array when I specify it as single?

Question

The documentation from get_post_meta makes it sound as if the single argument will determine whether or not meta values are returned in an array or not. For example:

// If I set single to false, or leave it blank it's returned as an array
[my-meta] => Array
    (
        [0] => my-value
    )

// If I set single to true, it's returned as a string
[my-meta] = my-value

This works fine if I'm only returning data for a single meta key...but fails if I want to return all of the meta data, but return them all as strings (single).

It would seem that the proper call to get all of the meta values with string values would be:

$meta = get_post_meta( $transaction->ID, false, true );

But this returns with the array values and completely ignores the single value.

Why? Is there a way to get all of the meta data, but without the single element arrays? Those are unnecessary in my case.

EDIT: Just to clarify what I'm asking, I'd lie to get all of the meta like this:

array() {
    [my-meta-1] = my-value
    [my-meta-2] = my-value
    [my-meta-3] = my-value
    [my-meta-4] = my-value
}

Rather than like this (which is the only behavior I seem to be able to get):

array() {
    [my-meta-1] => Array
    (
        [0] => my-value
    )
    [my-meta-2] => Array
    (
        [0] => my-value
    )
    [my-meta-3] => Array
    (
        [0] => my-value
    )
    [my-meta-4] => Array
    (
        [0] => my-value
    )
}

Answer 1

This works fine if I'm only returning data for a single meta key...but fails if I want to return all of the meta data, but return them all as strings (single).

This doesn't make a lot of sense. A function in PHP can only return a single value so there is no way to return all meta as strings (plural). It has to come out as an array, or an object. And that is what the function does-- you get a single value as a string or you get an array. If you don't specify a key then the code has no way to know which key you want so you get them all, by defaurl not single. When you are not retrieving single values, WordPress does not collapse the nested array. If that is what you want, take it up with the Core developers on Trac. In the meantime, collapse the array yourself:

$meta = get_post_meta(350);
var_dump($meta);
foreach ($meta as $k => $v) {
  $meta[$k] = array_shift($v);
}

Or:

foreach ($meta as &$v) {
  $v = array_shift($v);
}

That may not bet he answer you hoped for, but I am pretty sure it is accurate. There might be a filter, but I doubt the effort would be worth it.

Answer 2

A short little function, perhaps:

function get_post_meta_single( $id ) {
  $m = get_post_meta( $id, false, true );    // get post meta as singles
  foreach( $m as &$v ) $v = array_shift($v); // collapse value array
  return $m;
}

As a side note, it's likely that the reason that WordPress doesn't collapse the array is to maintain consistency, so the same code can be reused for items with multiple values and single values. WordPress is all about the loop, remember.