Apply transforms to linkage about json-api HOT 2 CLOSED

The problem with the approach above is that, after the transformation, the new linkage will have to be extracted from the returned resource, and the semantics for that aren't clear. What happens if the transform returns a resource object with no relationship at the path where the linkage was passed in? What happens if it return a resource with multiple relationships? What happens to those extra ones? Etc.

A more unified model would be to have beforeRender/beforeSave receive a resource or a resource identifier object. Then, primary data is represented by: an list of items, a flag for whether the items are full resources or resource identifiers, and a flag for whether the result is semantically singular (in which case the empty list is rendered as null, and the non-empty list is rendered as list[0]). Mapping over that becomes mapping over the internal list and, if it can return a promise for a new result, that logic implements the beforeRender transform.

Let's do the above, but then make whether to transform linkage opt-in through a setting on each type's description. We'll wrap the function we pass to map to do an if instanceof Linkage && registry.tranformLinkage ? userbeforeRender : id.

from json-api.

Addressed in c79ec4e

from json-api.