Changing a parent then unload a child record clears the hasMany relationship current state of the parent

[lsg-braymon]

Reproduction

• Pull Request Link: [TEST] - Unload record clears the current state of a has many relationship #6147

Description

1. Model setup:

   class Person extends Model {
     @hasMany('pet', { inverse: 'owner', async: false })
     pets;
     @attr()
     name;
   }
   
   class Pet extends Model {
     @belongsTo('person', { inverse: 'pets', async: false })
     owner;
     @attr()
     name;
   }

2. Data:

   personA:
     pets: petA
   
   personB:
     pets: petB
   

3. Update the owner of petB so that it is now owned by personA:

   petB.set("owner", personA)
   
   // It will result in the following relatioships:
   personA.pets // [petA, petB]
   personB.pets // []

4. Unload the original pet of personA which is petA: petA.unloadRecord().
5. Inspect the relationships:

   petB.owner // personA
   personA.pets // BUG: this is now empty. The expected result is [petB]

Versions

Run the following command and paste the output below: npm ls ember-source && npm ls ember-cli && npm ls ember-data.

ember-source@3.10.0
ember-source@3.10.0
ember-data@3.11.0-beta.1

We were also using ember-data@3.10.0 before and the issue is also present in that version.

[runspired]

This was fixed at some point with all of the relationship layer cleanup :)