When importing data using the Migrate module and the concat process plugin (, if the data source has empty values, the delimiter is included anyways.


id value_1 value_2
1 'Value 1' 'Value 2'
2 'Value 1'
3 'Value 2'

If I'd wanted to have a migration that used concat to join value_1 and value_2 I'd have these settings:

    plugin: concat
      - value_1
      - value_2
    delimiter: ' & '

Which will result in the following data:

id join value
1 'Value 1 & Value 2'
2 'Value 1 & '
3 ' & Value 2'
4 ' & '

I don't think 2, 3 and 4 are the desired result.

Proposed resolution

Add an array filter to strip out empty values when concat'ing. I don't see a use case of wanting these empty values, but this could be optional.

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pcambra created an issue. See original summary.

pcambra’s picture

Status: Active » Needs review
710 bytes
pcambra’s picture

Issue summary: View changes
Jo Fitzgerald’s picture

Status: Needs review » Needs work
Issue tags: +Needs tests

Firstly, this will need a test to demonstrate the problem (and prove that the patch fixes it). Secondly, perhaps we should add "allow_empty" to the plugin configuration (probably set to false by default) for those (rare) cases when I user might want ' & Value 2' (or similar).

pcambra’s picture

Thanks for the tags Jo, obviously this needs tests and a decision on the allow_empty option, I'll wait for a component maintainer to chime in before investing in adding those.

quietone’s picture

Yea, Jo Fitzgerald is on it, as usual. Everything in #4 sounds like a good implementation, with the addition of updating the API documentation will need updating.

Jo Fitzgerald’s picture

  • Added allow_empty to the plugin configuration (and relevant documentation).
  • Added tests (and tidied up the existing tests in the process which I think is acceptable as part of this issue considering the amount the tests are changing).

The last submitted patch, 7: 2913428-7-test_only.patch, failed testing. View results

heddn’s picture

Version: 8.5.x-dev » 8.4.x-dev
Status: Needs review » Reviewed & tested by the community

Looks good to me. Docs are added and tests too. I don't think we need a CR for the very minor API addition. This can probably make its way into 8.4, since migrate is still beta/experimental. So I've switched back versions. And adding a test for good measure.

quietone’s picture

Status: Reviewed & tested by the community » Needs work

Really sorry to set this back to NW. Using the structure 'if set' was pointed out in another migration issue (which of course I can't find) so let's use it here.

+++ b/core/modules/migrate/src/Plugin/migrate/process/Concat.php
@@ -16,6 +16,8 @@
+ * - allow_empty: (optional) Whether empty values should be included in the

It would be better and be consistent with the other process plugin docs to use something like; '(optional) If set, empty values will be included in the output. Defaults to FALSE.'

Jo Fitzgerald’s picture

Status: Needs work » Needs review
642 bytes
5.56 KB

Updated the comment for consistency, as suggested by @quietone.

heddn’s picture

Status: Needs review » Reviewed & tested by the community

Docs fixes added in response to #10. Back to RTBC.

quietone’s picture

@Jo Fitzgerald, thanks!

alexpott’s picture

Status: Reviewed & tested by the community » Needs review

I wonder if changing the default behaviour is a good idea - someone's migrations could be relying on this? Maybe we should swap the configuration default?

alexpott’s picture

Status: Needs review » Needs work
Issue tags: +Needs change record

Also migrate is beta and this plugin is part of the API so this needs a change record.

Jo Fitzgerald’s picture

Status: Needs work » Needs review
5.35 KB
6.17 KB

I have attempted to address @alexpott's very valid argument in #14. I have corrected that oversight, but in doing so I have come across a problem: when exclude_empty is TRUE zero values are excluded (when they shouldn't be, imo). Any suggestions?

heddn’s picture

Honestly, this whole piece of work seems a little like we could either 1) move it to contrib - migrate_plus is a good landing place or 2) leave it to a custom extention. Where in core do we need this functionality? Can we get a convincing argument why filtering empty is needed? we can always run array_filter with a callback process plugin beforehand, no?

Status: Needs review » Needs work

The last submitted patch, 16: 2913428-16.patch, failed testing. View results

Version: 8.4.x-dev » 8.5.x-dev

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