You might take a look at the Query annotation of Spring Data. It enables you to execute custom queries without the need of a custom controller.
Edit:
Query parameters are a good way to filter a resource by simple properties. As SDR serializes all complex types as relations, it is even clearer that filtering only applies to the remaining (simple) properties.
If you have only one relation, you correctly mentioned the way of doing the 'inverse' search as you called it by using /users/1/orders
.
If you want to search by multiple relations I suggest you define a seperate search (sub-)resource and perform the search by issuing a POST-request to this resource.
For example:
POST /orders/search
{
"user": "http://example.org/users/1",
...
}
This way, SDR will correctly translate the URIs into entities. However, I think you will need to use a custom controller here but it should be possible to still use the Spring Data repository and provide the user and additional entities as parameter.
For further information, see the following SO-questions:
How to design RESTful search/filtering?
RESTful URL design for search
Edit2:
Addressing the point that using a POST for searching violates the REST spec:
REST was designed to be simple. One of the key advantages of REST is that you are not forced to do anything. You can adapt the spec until it fits your needs. Of course, this could mean that your API is less RESTful but you should consider if it is worth it to strictly stick to the spec if it introduces an unnecessary overhead for the consumers of your API.
Of course you can design the above the idea to fully meet the REST spec. This would involve creating a seperate search entity, persisting it to the database and later retrieve the result of the search with a call to a subresource like /result
or something like that. However, the question is, if it is worth it.
In your concrete example, I would just require the client to parse the ID out of the link and provide it as query parameter. If you are scaling up your application later, you could introduce a feature like named searches and apply the above mentioned solution.