A model is a class that defines the properties and behavior of the data that you present to the user. Anything that the user expects to see if they leave your app and come back later (or if they refresh the page) should be represented by a model.
When you want a new model for your application you need to create a new file
under the models folder and extend from DS.Model
. This is more conveniently
done by using one of Ember CLI's generator commands. For instance, let's create
a person
model:
ember generate model person
This will generate the following file:
export default DS.Model.extend({
});
After you have defined a model class, you can start finding and working with records of that type.
Defining Attributes
The person
model we generated earlier didn't have any attributes. Let's
add first and last name, as well as the birthday, using DS.attr
:
export default DS.Model.extend({
firstName: DS.attr(),
lastName: DS.attr(),
birthday: DS.attr()
});
Attributes are used when turning the JSON payload returned from your server into a record, and when serializing a record to save back to the server after it has been modified.
You can use attributes like any other property, including as part of a computed property. Frequently, you will want to define computed properties that combine or transform primitive attributes.
export default DS.Model.extend({
firstName: DS.attr(),
lastName: DS.attr(),
fullName: Ember.computed('firstName', 'lastName', function() {
return `${this.get('firstName')} ${this.get('lastName')}`;
})
});
For more about adding computed properties to your classes, see Computed Properties.
Transforms
You may find the type of an attribute returned by the server does not
match the type you would like to use in your JavaScript code. Ember
Data allows you to define simple serialization and deserialization
methods for attribute types called transforms. You can specify that
you would like a transform to run for an attribute by providing the
transform name as the first argument to the DS.attr
method.
For example if you would like to transform an ISO 8601 string to a JavaScript date object you would define your attribute like this:
export default DS.Model.extend({
birthday: DS.attr('date')
});
Ember Data supports attribute types of string
, number
, boolean
,
and date
. Which coerce the value to the JavaScript type that matches
its name.
Transforms are not required. If you do not specify a transform name Ember Data will do no additional processing of the value.
Options
DS.attr
can also take a hash of options as a second parameter. At the moment
the only option available is defaultValue
, which can use a value or a function
to set the default value of the attribute if one is not supplied.
In the following example we define that verified
has a default value of
false
and createdAt
defaults to the current date at the time of the model's
creation:
export default DS.Model.extend({
username: DS.attr('string'),
email: DS.attr('string'),
verified: DS.attr('boolean', { defaultValue: false }),
createdAt: DS.attr('date', {
defaultValue() { return new Date(); }
})
});
Defining Relationships
Ember Data includes several built-in relationship types to help you define how your models relate to each other.
One-to-One
To declare a one-to-one relationship between two models, use
DS.belongsTo
:
export default DS.Model.extend({
profile: DS.belongsTo('profile')
});
export default DS.Model.extend({
user: DS.belongsTo('user')
});
One-to-Many
To declare a one-to-many relationship between two models, use
DS.belongsTo
in combination with DS.hasMany
, like this:
export default DS.Model.extend({
comments: DS.hasMany('comment')
});
export default DS.Model.extend({
post: DS.belongsTo('post')
});
Many-to-Many
To declare a many-to-many relationship between two models, use
DS.hasMany
:
export default DS.Model.extend({
tags: DS.hasMany('tag')
});
export default DS.Model.extend({
posts: DS.hasMany('post')
});
Explicit Inverses
Ember Data will do its best to discover which relationships map to one
another. In the one-to-many code above, for example, Ember Data can figure out that
changing the comments
relationship should update the post
relationship on the inverse because post
is the only relationship to
that model.
However, sometimes you may have multiple belongsTo
/hasMany
s for
the same type. You can specify which property on the related model is
the inverse using DS.belongsTo
or DS.hasMany
's inverse
option. Relationships without an inverse can be indicated as such by
including { inverse: null }
.
export default DS.Model.extend({
onePost: DS.belongsTo('post', { inverse: null }),
twoPost: DS.belongsTo('post'),
redPost: DS.belongsTo('post'),
bluePost: DS.belongsTo('post')
});
export default DS.Model.extend({
comments: DS.hasMany('comment', {
inverse: 'redPost'
})
});
Reflexive Relations
When you want to define a reflexive relation (a model that has a relationship to
itself), you must explicitly define the inverse relationship. If there
is no inverse relationship then you can set the inverse to null
.
Here's an example of a one-to-many reflexive relationship:
export default DS.Model.extend({
children: DS.hasMany('folder', { inverse: 'parent' }),
parent: DS.belongsTo('folder', { inverse: 'children' })
});
Here's an example of a one-to-one reflexive relationship:
export default DS.Model.extend({
name: DS.attr('string'),
bestFriend: DS.belongsTo('user', { inverse: 'bestFriend' }),
});
You can also define a reflexive relationship that doesn't have an inverse:
export default DS.Model.extend({
parent: DS.belongsTo('folder', { inverse: null })
});
Readonly Nested Data
Some models may have properties that are deeply nested objects of
readonly data. The naïve solution would be to define models for each
nested object and use hasMany
and belongsTo
to recreate the nested
relationship. However, since readonly data will never need to be
updated and saved this often results in the creation of a great deal
of code for very little benefit. An alternate approach is to define
these relationships using an attribute with no transform
(DS.attr()
). This makes it easy to access readonly values in
computed properties and templates without the overhead of defining
extraneous models.