如何使用 WordPress (PHP) 编写/读取和删除嵌套数组

Question

I've a bit of a problem realizing my plan. My initial situation is the following:

I have an array with different contents. In this example it looks like this:

$tmp[ get_current_user_id() ] = array(
    'id'      => 5,
    'ref'     => true
);

Now I want to save this array under a certain key using the function add_post_meta() in WordPress, which works so far:

add_post_meta( $post_id, 'tmp', $tmp );

As you can see above, I took the current User-ID for the key of the array. If I now have 2 entries in my array and output it, I have the following scheme:

$tmp = get_post_meta( $post_id, 'tmp' );

error_log( print_r( $tmp, true ) );

----------------------------------------

Array
(
    [0] => Array
        (
            [32] => Array
                (
                    [id] => 10
                    [ref] => 
                )

        )
    [1] => Array
        (
            [44] => Array
                (
                    [id] => 20
                    [ref] =>
                )

        )
)

At this point, however, I am not getting any further. For me, there are now two questions:

1. How can I access the correct array using the get_current_user_id() (as my key) function without running through multiple loops?
2. How can I now delete the entry with the User-ID 44 so that my array looks like this?:

Result after deletion:

Array
(
    [0] => Array
        (
            [32] => Array
                (
                    [id] => 10
                    [ref] => 
                )

        )
)

There is a function delete_post_meta() , but I don't know how it should work with nested arrays. I am very grateful for any help!

Answer 1

add_post_meta ( https://developer.wordpress.org/reference/functions/add_post_meta/ ) has a $unique flag defaulting to false. That is what causes the outer array - each time you add a new single element array with an id and ref, it is just appended to a list of elements under tmp .

However, if you enable $unique , you will overwrite the existing array each time - which I assume is not what you want, either. Therefore, instead of using add_post_meta , you should do the following:

1. get tmp post meta and store it in a variable
2. add user ID => value pair to the variable
3. use update_post_meta to overwrite tmp with the modified array

For get_post_meta , make sure to set $single to true (3rd argument) - otherwise you will again get it wrapped in an outer array):

// step 1: retrieve current value of 'tmp' meta
$user_list = get_post_meta($post_id, 'tmp', true);
if ($user_list === false) { // meta wasn't set yet
    $user_list = []; // initialize array
}

// step 2: set information for current user
$user_list[ get_current_user_id() ] = [ 'id' => 1337, 'ref' => '...'];

// step 3: overwrite 'tmp' post meta with updated array
update_post_meta($post_id, 'tmp', $user_list);

To then delete an element, do the following:

$user_list = get_post_meta($post_id, 'tmp', true);
if ($user_list === false) { // meta wasn't set yet
    $user_list = []; // initialize array
}

// step 2: delete desired user using unset
$user_id_to_delete = 44;
unset($user_list[ $user_id_to_delete ]);

// step 3: overwrite 'tmp' post meta with updated array
update_post_meta($post_id, 'tmp', $user_list);

Reading would work like this (only using get_post_meta ):

$user_list = get_post_meta($post_id, 'tmp', true);
if ($user_list === false) { // meta wasn't set yet
    $user_list = []; // initialize array
}

// iterate over all entries
foreach ($user_id => $user_info) {
    echo "User $user_id: ".json_encode($user_info).'<br/>'.PHP_EOL;
}
// read a single user's entry:
$user_id = 32;
echo "User ${user_id}'s entry: ".json_encode( $user_list[$user_id] ).
     '<br/>'.PHP_EOL;