Content fields on named parts are not indexed in SQL

[barthamark]

Describe the bug

Content field values are not indexed if those are attached to a content part used as a named part on a content item. Fields attached directly to the content type, however, are indexed as expected.

To Reproduce

Prerequisites: Make sure SQL field indexing feature is enabled.

Steps to reproduce the behavior:

1. Go to Admin UI > Content > Content Parts
2. Create a Content Part and edit it
   • Set Reusable to true
   • Add some field (e.g., a TextField)
   • Save
3. Go to Admin UI > Content > Content Types
4. Create a Content Type and edit it
   • Add a named part using the content part you've created previously.
   • Add a content field to the content type directly for observing proper indexing for this field
   • Save
5. Create a content item using the type you've previously created
   • Set the two field values you've attached: the one from the named part and the other one attached directly to the type
   • Save
6. Open SSMS / DB Browser for SQLite depending on the database type.
   • Open the related index table (e.g., TextFieldIndex)

Actual result

Observe the field value on the named part is not indexed, however, the one attached to the type directly is properly indexed.

Expected behavior

The field attached to the named part should be indexed. The ContentPart value should be the name of the named part.

[hishamco]

/cc @Skrypt

[Skrypt]

Probably in the same spirit of the existing module but as a feature of that module. Indexing these records fills up the database quick. It's always better to have custom indexing providers per content type / content part so that it can be fine tuned. Not against the idea, I think it would be a good addition. This and other suggestions that has been made over time for this module. We should probably tag the issues about this module and regroup the ideas.