Adding Custom Fields to the Field Edit Screen in Drupal 8 / 9


I’m building an API with Drupal 8/9. There is additional information I want to track against each field instance in each content type (or custom entity type) in the system. This information includes where the field’s data comes from, who is responsible for maintaining it, etc. This is useful for the site administrator and developers to track where things are coming from. Drupal’s Third Party Settings functionality makes this easy.


This is what you see when you edit the First name field:

When you click Save settings the data is saved to this specific field’s instance configuration (meaning if you reuse this field you can fill the info out differently per instance).


There are two ways to achieve this. In both cases, we use hook_form_FORM_ID_alter() to introduce the new fields. I am doing this within a custom module called pdms. The code lives in pdms.module.

Method #1:

With this method, the system automatically handles storing the value into the field configuration’s third party settings.

This happens because we use the  third_party_settings  key.

The issue I had with this approach is that I could not get it to work if I put the fields in a fieldset (as shown in the screenshot).

I think it’d be a matter of getting $entity->getThirdPartySetting()  to look into the fieldset somehow. If you know how to do this, please let me know!

Method #2:

This method gives us more control over what happens when the form is submitted.

Because we have more control we’re able to traverse the fieldset easily.

You can see, too, how I unset the third party setting if the value is empty. I am not sure if I’ll keep this in place; we’ll see if it causes any issues when I attempt to build a report showing all of the fields and their info.


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