Resource embedding across different schemas

[steve-chavez]

Resource Embedding only supports embedding across a single schema.

According to the profile negotiation spec:

A client requests an XML document where the elements in namespace urn:example:namespaces:ns1 must conform to XML schema http://example.com/schema/schema-1 and the elements in namespace urn:example:namespaces:ns2 must conform to XML schema http://example.com/schema/schema-2. The server answers that it can supply the document as requested.

Request:
GET /some-resource HTTP/1.1
Accept-Profile: <urn:example:namespaces:ns1
http://example.com/schema/schema-1
urn:example:namespaces:ns2
http://example.com/schema/schema-2>

Response:
HTTP/1.1 200 OK
Content-Type: application/xml
Profile: <urn:example:namespaces:ns1
http://example.com/schema/schema-1
urn:example:namespaces:ns2
http://example.com/schema/schema-2>

The spec is more XML focused but I believe we can extend the same concept of "elements in namespace must conform to XML schema" to "relations must conform to schema". So this would allow us to do:

GET /projects?select=*,clients(*)

Accept-Profile: <projects:api_v1 clients:api_v2>

Where projects comes from the api_v1 schema and clients comes from the api_v2 schema.

I'm still unclear on how to structure the absolute URLs for our case, but in theory it seems possible.

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The resource embedding code is actually ready for handling different schemas, we just need code for mapping the header.

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Related #2769

[wolfgangwalther]

I don't see why we would want to allow resource embedding across different profiles. When I remember correctly, you tried hard to make sure that schemas accessed through profiles are isolated from each other - there's a few test cases for that, too, right?

[steve-chavez]

Ditching this idea. No longer think is good for an API schema to allow cross resource embedding.

We'll likely move from the Accept-Profile header too #2927