Question: What is the links object used for?

[gracedo]

It's not entirely clear from the specs how the links object should be used. What urls can it hold? Must it only contain links to the resource url that the request is being made for? That seems to be the pattern according to the examples given, but the specs don't actually explain what these links need to be. Also, is the links object required with every resource response?

[masterspambot]

It's used to represent url linkage between objects, mainly used in communication system-to-system. For most simple cases you can use it to just keep url to current resource aka self.

And they are optional.

[gracedo]

It was proposed in one of my projects to populate the links object with a url to a file download. Would it be appropriate by jsonapi convention to use the links object for such a url, or should they only be used to link to resources?

[vrybas]

@gracedo,

url to a file download

Sounds like an object attribute to me. links object is more related to
the spec itself.

Note: Additional members may be specified for links objects and link
objects in the future.
http://jsonapi.org/format/#document-links

You wouldn't want your included custom attributes to conflict with
the changes in spec.

[ethanresnick]

links is optional everywhere but, for now, can only hold specific, spec-defined members. We'll likely open up links for holding urls with custom meanings in the future