Migrate sub_process plugin is not working

Question

There are a couple of questions that are closely related to this on this forum that I have reviewed several times. None of them seem to address the issue specifically.

I have a target field (with subfields) that is set to unlimited.

The Source that I'm "migrating" from is JSON. The Target, in this case, is an address field on a node.

To simplify and debug the migration. I created a constant as a source for the values that I want to assign to field_locations/country_code.

The code in the migration configuration YAML is

source:
  constants:
    title_suffix: ' (Imported from remote file)'
    country: 'GB'
    countries:
      -
        country: US
      -
        country: CA
....

process:
  field_locations:
      plugin: sub_process
      source: 
        - constants/countries
      process:
        country_code: country

If I replace the implementation of the sub_process plugin and use get, I update the target field (subfield actually) with:

field_locations/country_code: constants/country

The destination row is updated perfectly - though of course I can only et

For reference: This is what the entity should look like with repeating values set. How do I get that to work with this migration? I'm guessing there is something pretty simple I'm missing

Answer 1

OK - I spent far more time than I care admit debugging this one. (doesn't help that PHPStorm is very unfriendly when it comes to stepping through a migration (e.g. I have not found a way to do it). Hope this saves someone from the frustration I had.

Problem one: Source was not formatted correctly. It MUST follow the following structure:

$source = [
  'countries' => [
    0 => [
      'country' => 'US',
    ],
    1 => [
      'country' => 'CA',
    ],
  ],
];

The YAML for that is:

  constants:
    countries:
      - country: 'US'
      - country: 'CA'

Problem two: The implementation of sub_process was a little off. And a little off is like being on the wrong planet. It should like this

  field_locations:
    plugin: sub_process
    source: constants/countries
    process:
      country_code: country 

One thing that is not obvious (and would never be if you were actually "migrating" from D7 to D8 for example, is the source.

Here, I am not actually migrating. It is an import from JSON. And, as it turns out, importing JSON can be a little unpredictable. The final "gotcha" was that the key "country" had to relate to the source (which it usually does). I had tried to slap in a different constant. (bad idea - though it could be done if that is really what is wanted.