`apispec` ignores `oneOf` from `marshmallow-oneofschema`

[mjdominus]

I need oneOf in my schema:

class AerthlingsShopOffer(OneOfSchema):
    """Polymorphic offer type discriminated by the 'type' field."""
    type_field = "type"
    type_schemas = {
        "character": AerthlingsCharacterOffer,
        "mutation_point": AerthlingsMpOffer,
    }

Marshmallow doesn't seem to support this. Fortunately, there is an extension, marshmallow-oneofschema. Unfortunately, when presented with the class above, apispec silently ignores it, producing

            "AerthlingsShopOffer": {
                "type": "object",
                "properties": {}
            },

and omitting AerthlingsCharacterOffer and AerthlingsMpOffer entirely.

I have a fix for this, but I think it requires discussion, and I have not yet written a unit test for it. If you think this is worth doing, I can complete the work and submit a PR. If not, that is no problem for me; I can continue to use my forked apispec in my own project.

[lafrech]

Indeed apispec doesn't support marshmallow-oneofschema.

I'm reluctant to add it as a dependency. However if the change can be achieved without depending on it, I don't mind adding it as a test dependency. Alright, maybe we can make it an optional dependency if needed.

[Bangertm]

It’s been a while, but I believe apispec-oneofschema should still work for this use case.

[mjdominus]

I'm reluctant to add it as a dependency. However if the change can be achieved without depending on it, I don't mind adding it as a test dependency. Alright, maybe we can make it an optional dependency if needed.

The patch works even if marshmallow-oneofschema is unavailable. It's conditionalized:

+        # Check if this is a OneOfSchema from marshmallow-oneofschema
+        try:
+            from marshmallow_oneofschema import OneOfSchema
+
+            if isinstance(schema, OneOfSchema):
+                return self._oneof_schema2jsonschema(schema)
+        except ImportError:
+            pass

I've attached the whole thing here in case any other details are of interest.

PATCH.txt

I don't like the hardwired special case for marshmallow_oneofschema, and this is one of the things I thought required discussion.

If there's already a plugin architecture that supports apispec-oneofschema then any support for marshmallow-oneofschema should probably use the same mechanism, and not this hack.

[lafrech]

I'd rather the import be tested once at import time. E.g.

    try:
        from marshmallow_oneofschema import OneOfSchema
        ONEOFSCHEMA_AVAILABLE = True
    except ImportError:
        ONEOFSCHEMA_AVAILABLE = False

Then

     if ONEOFSCHEMA_AVAILABLE and isinstance(schema, OneOfSchema):
         return self._oneof_schema2jsonschema(schema)

[mjdominus]

Sure, I can easily do that.

I've also made further revisions to the patch. If the input is

• A is oneOf B₁ or B₂
• B₁ and B₂ inherit from the same base class B that includes field f
• But each of B₁ and B₂ also includes some variant-specific data that is not in the other one

then the output for B₁ now looks like this:

allOf: [
    { "$ref": "B" },
    { "type": "object", "properties": { (properties specific to B₁) }, … }
]

and B₂ similarly.

If you folks want any or all of this, I will be happy to put it together and submit a PR. If not, that's fine too, but then we should close the discussion.

[lafrech]

Please open a PR.

Thanks.