Backbone-relational
Backbone-relational provides one-to-one, one-to-many and many-to-one relations between models for Backbone. To use relations, extend Backbone.RelationalModel
(instead of the regular Backbone.Model
) and define a property relations
, containing an array of option objects. Each relation must define (as a minimum) the type
, key
and relatedModel
. Available relation types are Backbone.HasOne
and Backbone.HasMany
. Backbone-relational features:
- Bidirectional relations, which notify related models of changes through events.
- Control how relations are serialized using the
includeInJSON
option. - Automatically convert nested objects in a model's attributes into Model instances using the
createModels
option. - Retrieve (a set of) related models through the
fetchRelated(key<string>, [options<object>])
method. - Determine the type of
HasMany
collections withcollectionType
. - Bind new events to a
Backbone.RelationalModel
for:- addition to a
HasMany
relation (bind toadd:<key>
; arguments:(addedModel, relatedCollection)
), - removal from a
HasMany
relation (bind toremove:<key>
; arguments:(removedModel, relatedCollection)
), - reset of a
HasMany
relation (bind toreset:<key>
; arguments:(relatedCollection)
), - changes to the key itself on
HasMany
andHasOne
relations (bind toupdate:<key>
; arguments=(model, relatedModel/relatedCollection)
).
- addition to a
Contents
- Installation
- Backbone.Relation options
- Backbone.RelationalModel
- Example
- Known problems and solutions
- Under the hood
Installation
Backbone-relational depends on backbone (and thus on underscore). Include Backbone-relational right after Backbone and Underscore:
<script type="text/javascript" src="./js/underscore.js"></script>
<script type="text/javascript" src="./js/backbone.js"></script>
<script type="text/javascript" src="./js/backbone-relational.js"></script>
Backbone-relational has been tested with Backbone 0.5.3 (or newer) and Underscore 1.2.1 (or newer).
Backbone.Relation options
Each Backbone.RelationalModel
can contain an array of relations
.
Each relation supports a number of options, of which relatedModel
, key
and type
are mandatory.
A relation could look like the following:
Zoo = Backbone.RelationalModel.extend({
relations: [{
type: Backbone.HasMany,
key: 'animals',
relatedModel: 'Animal',
collectionType: 'AnimalCollection',
reverseRelation: {
key: 'livesIn',
includeInJSON: 'id'
// 'relatedModel' is automatically set to 'Zoo'; the 'relationType' to 'HasOne'.
}
}]
});
Animal = Backbone.RelationalModel.extend({
urlRoot: '/animal/'
});
AnimalCollection = Backbone.Collection.extend({
model: Animal,
url: function( models ) {
return '/animal/' + ( models ? 'set/' + _.pluck( models, 'id' ).join(';') + '/' : '' );
}
});
relatedModel
Value: a string (which can be resolved to an object type on the global scope), or a reference to a Backbone.RelationalModel
type.
key
Value: a string. References an attribute name on relatedModel
.
type
Value: a string, or a reference to a Backbone.Relation
type
Example: Backbone.HasOne
or 'HasMany'
.
Backbone.HasOne
)
HasOne relations (The key for a HasOne
relation consists of a single Backbone.RelationalModel
. The default reverseRelation.type
for a HasOne relation is HasMany.
This can be set to HasOne
instead, to create a one-to-one relation.
Backbone.HasMany
)
HasMany relations (The key for a HasMany
relation consists of a Backbone.Collection
, containing zero or more Backbone.RelationalModel
s.
The default reverseRelation.type
for a HasMany relation is HasOne; this is the only option here, since many-to-many is not supported directly.
Many-to-many relations
A many-to-many relation can be modeled using two Backbone.HasMany
relations, with a link model in between:
Person = Backbone.RelationalModel.extend({
relations: [
{
type: 'HasMany',
key: 'jobs',
relatedModel: 'Job',
reverseRelation: {
key: 'person'
}
}
]
});
// A link object between 'Person' and 'Company', to achieve many-to-many relations.
Job = Backbone.RelationalModel.extend({
defaults: {
'startDate': null,
'endDate': null
}
})
Company = Backbone.RelationalModel.extend({
relations: [
{
type: 'HasMany',
key: 'employees',
relatedModel: 'Job',
reverseRelation: {
key: 'company'
}
}
]
});
niceCompany = new Company( { name: 'niceCompany' } );
niceCompany.bind( 'add:employees', function( model, coll ) {
// Will see a Job with attributes { person: paul, company: niceCompany } being added here
});
paul.get('jobs').add( { company: niceCompany } );
collectionType
Value: a string (which can be resolved to an object type on the global scope), or a reference to a Backbone.Collection
type.
Determine the type of collections used for a HasMany
relation. If you define a url(models<Backbone.Model[]>)
function on
the specified collection, this enables fetchRelated
to fetch all missing models in one request, instead of firing a separate request for each.
See Backbone-tastypie for an example
of a url
function that can build a url for the collection (or a subset of models).
collectionKey
Value: a string or a boolean
By default, the relation's key
attribute will be used to create a reference to the RelationalModel instance from the generated collection.
If you set collectionKey
to a string, it will use that string as the reference to the RelationalModel, rather than the relation's key
attribute.
If you don't want this behavior at all, just set collectionKey
to false (or any falsy value) and this reference will not be created.
includeInJSON
Value: a boolean, or a string referencing one of the model's attributes. Default: true
.
Determines how a relation will be serialized following a call to the toJSON
method. A value of true
serializes the full set of attributes
on the related model(s), in which case the relations of this object are serialized as well. Set to false
to exclude the relation completely.
You can also choose to include a single attribute from the related model by using a string.
For example, 'name'
, or Backbone.Model.prototype.idAttribute
to include ids.
createModels
Value: a boolean. Default: true
.
Should models be created from nested objects, or not?
reverseRelation
If the relation should be bidirectional, specify the details for the reverse relation here.
It's only mandatory to supply a key
; relatedModel
is automatically set. The default type
for a reverseRelation
is HasMany
for a HasOne
relation (which can be overridden to HasOne
in order to create a one-to-one relation), and HasOne
for a HasMany
relation. In this case, you cannot create a reverseRelation with type HasMany
as well; please see Many-to-many relations on how to model these type of relations.
Please note: if you define a relation (plus a reverseRelation
) on a model, but never actually create an instance of that model, the model's constructor
will never run, which means it's initializeRelations
will never get called, and the reverseRelation will not be initialized either. In that case, you could either define the relation on the opposite model, or define two single relations. See issue 20 for a discussion.
Backbone.RelationalModel
Backbone.RelationalModel
introduces a couple of new methods and events.
Methods
relationalModel.getRelations()
getRelations Returns the set of initialized relations on the model.
relationalModel.fetchRelated(key<string>, [options<object>])
fetchRelated Fetch models from the server that were referenced in the model's attributes, but have not been found/created yet. This can be used specifically for lazy-loading scenarios.
By default, a separate request will be fired for each additional model that is to be fetched from the server.
However, if your server/API supports it, you can fetch the set of models in one request by specifying a collectionType
for the relation you call fetchRelated
on. The collectionType
should have an overridden url(models<Backbone.Model[]>)
method that allows it to construct a url for an array of models.
See the example at the top of Backbone.Relation options or
Backbone-tastypie for an example.
Events
add
: triggered on addition to aHasMany
relation.
Bind toadd:<key>
; arguments:(addedModel<Backbone.Model>, related<Backbone.Collection>)
.remove
: triggered on removal from aHasMany
relation.
Bind toremove:<key>
; arguments:(removedModel<Backbone.Model>, related<Backbone.Collection>)
.update
: triggered on changes to the key itself onHasMany
andHasOne
relations.
Bind toupdate:<key>
; arguments:(model<Backbone.Model>, related<Backbone.Model|Backbone.Collection>)
.
Example
paul = new Person({
id: 'person-1',
name: 'Paul',
user: { id: 'user-1', login: 'dude', email: 'me@gmail.com' }
});
// A User object is automatically created from the JSON; so 'login' returns 'dude'.
paul.get('user').get('login');
ourHouse = new House({
id: 'house-1',
location: 'in the middle of the street',
occupants: ['person-1', 'person-2', 'person-5']
});
// 'ourHouse.occupants' is turned into a Backbone.Collection of Persons.
// The first person in 'ourHouse.occupants' will point to 'paul'.
ourHouse.get('occupants').at(0); // === paul
// If a collection is created from a HasMany relation, it contains a reference
// back to the originator of the relation
ourHouse.get('occupants').livesIn; // === ourHouse
// the relation from 'House.occupants' to 'Person' has been defined as a bi-directional HasMany relation,
// with a reverse relation to 'Person.livesIn'. So, 'paul.livesIn' will automatically point back to 'ourHouse'.
paul.get('livesIn'); // === ourHouse
// You can control which relations get serialized to JSON (when saving), using the 'includeInJSON'
// property on a Relation. Also, each object will only get serialized once to prevent loops.
paul.get('user').toJSON();
/* result:
{
email: "me@gmail.com",
id: "user-1",
login: "dude",
person: {
id: "person-1",
name: "Paul",
livesIn: {
id: "house-1",
location: "in the middle of the street",
occupants: ["person-1"] // just the id, since 'includeInJSON' references the 'idAttribute'
},
user: "user-1" // not serialized because it is already in the JSON, so we won't create a loop
}
}
*/
// Load occupants 'person-2' and 'person-5', which don't exist yet, from the server
ourHouse.fetchRelated( 'occupants' );
// Use the 'add' and 'remove' events to listen for additions/removals on HasMany relations (like 'House.occupants').
ourHouse.bind( 'add:occupants', function( model, coll ) {
// create a View?
console.debug( 'add %o', model );
});
ourHouse.bind( 'remove:occupants', function( model, coll ) {
// destroy a View?
console.debug( 'remove %o', model );
});
// Use the 'update' event to listen for changes on a HasOne relation (like 'Person.livesIn').
paul.bind( 'update:livesIn', function( model, attr ) {
console.debug( 'update to %o', attr );
});
// Modifying either side of a bi-directional relation updates the other side automatically.
// Make paul homeless; triggers 'remove:occupants' on ourHouse, and 'update:livesIn' on paul
ourHouse.get('occupants').remove( paul.id );
paul.get('livesIn'); // yup; nothing.
// Move back in; triggers 'add:occupants' on ourHouse, and 'update:livesIn' on paul
paul.set( { 'livesIn': 'house-1' } );
This is achieved using the following relations and models:
House = Backbone.RelationalModel.extend({
// The 'relations' property, on the House's prototype. Initialized separately for each instance of House.
// Each relation must define (as a minimum) the 'type', 'key' and 'relatedModel'. Options are
// 'includeInJSON', 'createModels' and 'reverseRelation', which takes the same options as the relation itself.
relations: [
{
type: Backbone.HasMany, // Use the type, or the string 'HasOne' or 'HasMany'.
key: 'occupants',
relatedModel: 'Person',
includeInJSON: Backbone.Model.prototype.idAttribute,
collectionType: 'PersonCollection',
reverseRelation: {
key: 'livesIn'
}
}
]
});
Person = Backbone.RelationalModel.extend({
relations: [
{ // Create a (recursive) one-to-one relationship
type: Backbone.HasOne,
key: 'user',
relatedModel: 'User',
reverseRelation: {
type: Backbone.HasOne,
key: 'person'
}
}
],
initialize: function() {
// do whatever you want :)
}
});
PersonCollection = Backbone.Collection.extend({
url: function( models ) {
// Logic to create a url for the whole collection, or a set of models.
// See the tests, or Backbone-tastypie, for an example.
return '/person/' + ( models ? 'set/' + _.pluck( models, 'id' ).join(';') + '/' : '' );
}
});
User = Backbone.RelationalModel.extend();
Known problems and solutions
Q: Relations do not seem to be initialized properly.
A: This (mostly) seems to occur because a relation is defined in the reverseRelations
of another model, which hasn't
been instantiated yet (which in turn means it's relations
haven't been created yet, so the reverseRelation
hasn't been created yet either).
The current workaround is to create an instance of this other model first (this can be either a dummy that gets destroyed right away,
or one that you actually use).
Q: After a fetch,
add:<key>
events don't occur for nested relations.
A: This is due to the {silent: true}
in Backbone.Collection.reset
. Pass fetch( {add: true} )
to bypass this problem.
You may want to override Backbone.Collection.fetch
for this, and also trigger an event when the fetch has finished while you're at it.
Example:
var _fetch = Backbone.Collection.prototype.fetch;
Backbone.Collection.prototype.fetch = function( options ) {
options || ( options = {} );
_.defaults( options, { add: true } );
// Remove old models
this.reset();
// Call 'fetch', and trigger an event when done.
var dit = this,
request = _fetch.call( this, options );
request.done( function() {
if ( !options.silent ) {
dit.trigger( 'fetch', dit, options );
}
});
return request;
};
Under the hood
Each Backbone.RelationalModel
registers itself with Backbone.Store
upon creation (and is removed from the Store
when destroyed).
When creating or updating an attribute that is a key in a relation, removed related objects are notified of their removal,
and new related objects are looked up in the Store
.