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Relationships
Relationships are a core component of Ash. They provide a mechanism to describe the relationships between your resources, and through those relationships you can do things like
- Loading related data
- Filtering on related data
- Managing related records through changes on a single resource
- Authorizing based on the state of related data
Managing related data
See {{link:ash:guide:Managing Relationships}} for more information.
Loading related data
Loading relationships is a very common use case. There are two ways to load relationships, in the query, and on records.
On records
Given a set of records, like [user1, user2], you can load their relationships by calling your Ash Api's load function.
YourApi.load(users, :friends)
This will fetch the friends of each user, and set them in the corresponding friends key.
In the query
Loading in the query is currently pretty much the same as loading on records, but eventually data layers will be able to optimize these loads, potentially including them as joins in the main query, for example. The following will return the list of users with their friends loaded, as the above example.
User
|> Ash.Query.load(:friends)
|> YourApi.read()
More complex data loading
Multiple relationships can be loaded at once, i.e
YourApi.load(users, [:friends, :enemies])
Nested relationships can be loaded:
YourApi.load(users, friends: [:friends, :enemies])
The queries used for loading can be customized by providing a query as the value.
friends = Ash.Query.sort(User, social_score: :asc)
YourApi.load(users, friends: friends)
Nested loads will be included in the parent load.
friends =
User
|> Ash.Query.sort(social_score: :asc)
|> Ash.Query.load(:friends)
# Will load friends and friends of those friends
YourApi.load(users, friends: friends)