get_post_meta does not always return data in the same order

[mattheu]

get_post_meta does not always return data in the same order when returning an array of all meta values for a given key.

Expected outcome: I expect the order to remain the same every time this data is retrieved.

This usually returns data in the correct order but it is not guaranteed as the SQL query in the update_meta_cache function does not explicitly order by anything.

I propose that meta data should be explicitly ordered by meta_id.

I have a patch if this is considered a but

[mattheu]

Use case:

I have a plugin that allows users to add custom fields to the post edit screen. It is possible to create a field and add multiple values which are then stored as separate post meta entries using a single key. Users expect that the order of this data will be preserved.

When this data is saved, all previously stored data is deleted and then added again in the order it was submitted to ensure that the meta_id order corresponds to the desired order of the data.

[jeremyfelt]

Hi @mattheu, you mentioned having a patch in the ticket description. Can you upload this patch now so that we can see what kind of approach you had in mind?

[mattheu]

@jeremyfelt - patch added

[mattheu]

I've updated the patch to use a ternary operator for the orderby_column to be more consistent with the rest of the code base. Thanks @jeremyfelt

[mattheu]

Updated the patch so that variable name is more consitent with rest of codebase

[wonderboymusic]

25511.4.diff​​ ditches the unnecessary $wpdb->prepare call which was passing a variable to a SQL statement with no replacement tokens

[wonderboymusic]

In 26307:

In update_meta_cache(), ensure that meta is always stored in the same order. Removes an unnecessary $wpdb->prepare statement. Adds unit test.

Props mattheu.
Fixes #25511.

[nacin]

#25619 was marked as a duplicate.