inverse relationships not set up when pushing jsonapi blob with polymorphic model

[BryanCrotaz]

Single source of truth isn't working for polymorphic relationships.

Push a hasMany with a descendant model. You'd expect that the matching belongsTo on the descendant model points back to the parent model. Instead it's null.

This works if the child model is the type specified in the hasMany, but not if it's a descendant model.

store.push({
  data: { post with relationship to descendant comment1 },
  included: { descendant comment1 with missing post relationship }
})

post.get('comments') => [comment1]
comment1.get('post') => **null**

Workaround: add post relationship into comment1 in jsonapi

Working on a PR with test

[BryanCrotaz]

Test added in PR #5268

[BryanCrotaz]

@stefanpenner I'm not sure of the best way to fix this. The relationship-payload cache is keyed on baseClass:relationship so the entry isn't being found when you search for descendant:relationship.

We could add multiple cache entries for each of the different descendants, but I'm not sure how to discover them.

[BryanCrotaz]

I think I found a way... see PR for details

[bmac]

I believe this has been resolved by #5230. Feel free to reopen if it is still an issue.