flask-restless
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jfinkels
Regression: GET_SINGLE requests to parent class do not find instances of child classes
Considering having a model called A and a model called B, where B is a sublcass of A, there is an issue with getting single resources. A and B are polymorphic in SQLAlchemy.
GETing /api/A returns a list of all instances of A and B, but GETing /api/A/1 returns 404 if the object with id 1 is an instance of class B.
It should be possible to get resources of a child model by GETing it through the parent model endpoint.
This is a design decision I made in order for the different request methods (GET, POST, etc.) to be more uniform and to fit more cleanly with the requirements of the JSON API specification. See https://github.com/jfinkels/flask-restless/issues/200#issuecomment-220523164 for a summary of what is supported and what is not supported.
Basically, if we allow fetching from /api/A/1 then the response will be a JSON API resource object of type B: {'id': 1, 'type': 'B'}. Now what should its self URL be? Should requests to /api/B/1 be allowed? etc. There are many small issues like this, and I'm happy to receive advice on how to handle them.
I think as /api/A lists the resource, then it should also be available as /api/A/1. You either recognize as also being an instance of A or you don't, but you don't accept that it is of class A in GET_MANY, then deny it in GET_SINGLE.
its self link should probably point to the real type URL (it does so when being listed in /api/A, right?).
That would also match the polymorphism in SQLAlchemy.
Maybe it's even simpler, and you should really just rely on how SQLAlchemy is configured. That is, if the resource can be found by A.get(1) in Flask-SQLAlchemy, then Flask-Restless should deliver it. As this is nothing that would violate JSONAPI, Flask-Restless should choose to just not divert from Flask-SQLAlchemy's behaviour.
I guess following SQLAlchemy's lead makes sense. Let's first locate the relevant test cases that need to change in tests/test_polymorphism.py, then work from there.