Models
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Ember Data models are normal TypeScript classes, but with properties decorated to define how the model represents an API resource and relationships to other resources. The decorators the library supplies "just work" with TypeScript at runtime, but require type annotations to be useful with TypeScript.
For details about decorator usage, see .
@attr
The type returned by the @attr
decorator is whatever is applied via the invocation. See .
If you supply no argument to @attr
, the value is passed through without transformation.
If you supply one of the built-in transforms, you will get back a corresponding type:
@attr('string')
→ string
@attr('number')
→ number
@attr('boolean')
→ boolean
@attr('date')
→ Date
If you supply a custom transform, you will get back the type returned by your transform.
So, for example, you might write a class like this:
Very important: Even more than with decorators in general, you should be careful when deciding whether to mark a property as optional ?
or definitely present (no annotation): Ember Data will default to leaving a property empty if it is not supplied by the API or by a developer when creating it. That is: the default for Ember corresponds to an optional field on the model.
The safest type you can write for an Ember Data model, therefore, leaves every property optional: this is how models actually behave. If you choose to mark properties as definitely present by leaving off the ?
, you should take care to guarantee that this is a guarantee your API upholds, and that ever time you create a record from within the app, you uphold those guarantees.
One way to make this safer is to supply a default value using the defaultValue
on the options hash for the attribute:
@belongsTo
The type returned by the @belongsTo
decorator depends on whether the relationship is { async: true }
(which it is by default).
If the value is true
, the type you should use is AsyncBelongsTo<Model>
, where Model
is the type of the model you are creating a relationship to.
If the value is false
, the type is Model
, where Model
is the type of the model you are creating a relationship to.
So, for example, you might define a class like this:
These are type-safe to define as always present, that is to leave off the ?
optional marker:
accessing an async relationship will always return an AsyncBelongsTo<Model>
object, which itself may or may not ultimately resolve to a value—depending on the API response—but will always be present itself.
accessing a non-async relationship which is known to be associated but has not been loaded will trigger an error, so all access to the property will be safe if it resolves at all.
Note, however, that this type-safety is not a guarantee of there being no runtime error: you still need to uphold the contract for non-async relationships (that is: loading the data first, or side-loading it with the request) to avoid throwing an error!
@hasMany
The type returned by the @hasMany
decorator depends on whether the relationship is { async: true }
(which it is by default).
If the value is true
, the type you should use is AsyncHasMany<Model>
, where Model
is the type of the model you are creating a relationship to.
If the value is false
, the type is SyncHasMany<Model>
, where Model
is the type of the model you are creating a relationship to.
So, for example, you might define a class like this:
The same basic rules about the safety of these lookups as with @belongsTo
apply to these types. The difference is just that in @hasMany
the resulting types are arrays rather than single objects.
Relationships between models in Ember Data rely on importing the related models, like import User from './user';
. This, naturally, can cause a recursive loop, as /app/models/post.ts
imports User
from /app/models/user.ts
, and /app/models/user.ts
imports Post
from /app/models/post.ts
. Recursive importing triggers an error from eslint.
To avoid these errors, use , available since TypeScript 3.8: