Duplication of post meta keys

[arsendovlatyan]

I was testing Distributor with Woo-commerce (using external connection) and all of the sudden noticed that meta keys getting duplicated in destination, with every update i have more and more duplicated meta keys.

I'm not sure if this is related to 1.3.4 release or #200 , but couldn't find similar bug-report and want to make sure that you are aware about it.

P.C. i have used fresh WordPress install (4.9.8) with fresh WooCommerce (3.5.1) and last version of Distributor 1.3.4

@helen @dkotter want to make sure that you are aware about this issue, we are not using Distributor in production yet, but if other do, it can add a mess in post meta table.

@madmax3365 to follow

[jakemgold]

Likely related to 1.3.4 - we tried to handle a situation where the same meta key is used multiple times on the source side (intentionally - WordPress supports that use case) - and it seems likely that this is unintended side effect with WooCommerce. We'll look into, but in the mean time, you can always roll back to 1.3.3 via Github.

[helen]

@arsendovlatyan Looking into this - when you say "with every update", what kind of update are you talking about?

[arsendovlatyan]

@helen Just regular post update, from admin interface, in source/original website.
@jakemgold unfortunately, it's not related with WooCommerce, even if WooCommerce is disabled and testing on regular posts, it still have the same issue.

Original:

Distributed:

[jakemgold]

Quick clarification - we only see the empty "_test_meta" field being duplicated in your example; all the other fields seem fine. Can you confirm that all or some other fields are also duplicating? Is it just empty key values?

[arsendovlatyan]

Yes, I can confirm that only empty (or NULL) meta values will be duplicated.

[arsendovlatyan]

Please consider my pull request, since it will solve another issue as well - distribution of serialized meta values, currently it's not working.
We are using get_post_meta to retrieve existing meta values $existing_meta = get_post_meta( $post_id ); , because meta_key is not provided, maybe_unserialize won't be applied automatically, so, we have to apply it manually before using in update_post_meta as $prev_value argument.

I have tested many different cases, and seems like everything works fine.

The only thing that i have noticed, is when you have 2 or more meta values, with the same keys and one of them is empty ('' or 0), in that case, all meta values in distention will eventually be reset to empty.
In practice this case can happen only if there are update requests to database with meta ID, as much as I know, there is no built-in WordPress functions to handle such updates, so, it must be very rare case and can be handled by applying appropriate hooks.

[helen]

Commented on the PR about this too but also want to summarize here:

The only thing that i have noticed, is when you have 2 or more meta values, with the same keys and one of them is empty ('' or 0), in that case, all meta values in distention will eventually be reset to empty.

I think this is the same cause as what I saw in testing #259, which is that all those duplicated meta keys get set to the same value because of the way update_post_meta() works (doesn't take an ID). We also don't actually delete any meta at any point, so they just kind of linger there. I think we need to address post meta deletion for sure, but carefully and separately. For now, this is a good enough fix for 1.3.5 and I think will actually also alleviate a back-compat issue I noticed (although I didn't test to make sure it truly works correctly, it just won't fully break).