RESTful url - getting new subentity

Question

There are 2 models: Entity and Subentity. Entity can have many connected Subentities (one:many relation).

There is a method on server that returns new Subentity (let's call it GetEmptySubentity). Point is, when you want to create new Subentity, you press a button, and model comes from server with some fields pre-filled. Some of those Subentity pre-filled values depend on according Entity, so I need to pass an Entity id in this request.

So should the correct url to get the empty Subentity be like /Entity/{id}/Subentity/empty? Or I am getting something wrong?

Answer 1

Yes you are. According to the uniform interface / hateoas constraint you should send hyperlinks to your REST clients and they should use the API by following those hyperlinks. In order to do this you need a hypermedia format, for example HTML, ATOM+XML, HAL+JSON, LD+JSON & Hydra, etc... (use google). So by HTML the result should contain a HTML form with input fields having default values, etc... You should add semantics to that for with RDFa and so by processing the HTML your REST client will know, that the link is about creating a new resource. Ofc it is easier to parse the other hypermedia formats. By them you can use the same concept with RDF (by JSON-LD or ATOM for example), or you can use link relations with vendor specific MIME types (by HAL or ATOM for example), or your custom solution which describes those input fields. So you usually get the necessary information with the hyperlink, and you don't have to send another request to get the default values.

If you want to make things complicated, then you can send a request for the default values to the entity itself in order to send the values of properties, and not to send a form with input fields. Optionally you can send a request which returns the entire link, for example GET /Entity/{id}/SubEntity/offset=0&count=0 can return an empty array of subentities and the form for creation. You can use additional query or path parameters if that form is really big, and you don't want to send it with every response related to the SubEntity collection. The URL specification says only that the path should contain the hierarchical part and the query should contain the non-hierarchical part of the URL.

Btw. REST is just a delivery method, you don't have to map it to your database entities. The REST resource and URL structure can be completely different from your database, since you can use any type of data storage mechanisms with REST, even the file system...