Can a single Backbone Model Instance be in two collections at once? - backbone.js

I understand that it's "this.collection" value will only show the first collection, but is this otherwise compatible with Backbone? Or will it automatically get removed from the previous collection?
var MyModel = Backbone.Model.extend({defaults: {test: '123'}});
var MyCollection1 = Backbone.Collection.extend({model: MyModel});
var MyCollection2 = Backbone.Collection.extend({model: MyModel});
var instance = new MyModel({
test: '456'
});
MyCollection1.add(instance);
MyCollection2.add(instance);
console.log(instance.collection); //Returns "MyCollection1" only, not an array of all collections of which this model is a member
The above code works, I'm just wondering if I'm breaking anything (particularly related to events) by doing this.

TL;DR Nothing will break, you can verify this by looking at the source, add is a shorthand method for, set(model, {add: true, remove: false, merge: false})
If you look at the set method the part where it modifies the model is here,
_addReference: function(model, options) {
this._byId[model.cid] = model;
if (model.id != null) this._byId[model.id] = model;
if (!model.collection) model.collection = this;
model.on('all', this._onModelEvent, this);
},
So the models' collection will not be set to the new one if it already has one, but all events will still be passed through correctly from all collections it is added to.
The reverse is also true, any collection events are called by iterating on the models in the collection,
for (i = 0, l = models.length; i < l; i++) {
...
if (!options.silent) {
model.trigger('remove', model, this, options);
}
...
}

Related

Backbone.Model: set collection as property

I'm new with backbone and faced the following problems. I'm trying to emulate some sort of "has many relation". To achieve this I'm adding following code to initialize method in the model:
defaults: {
name: '',
tags: []
},
initialize: function() {
var tags = new TagsCollection(this.get('tags'));
tags.url = this.url() + "/tags";
return this.set('tags', tags, {
silent: true
});
}
This code works great if I fetch models through collection. As I understand, first collection gets the data and after that this collection populates models with this data. But when I try to load single model I get my property being overridden with plain Javascript array.
m = new ExampleModel({id: 15})
m.fetch() // property tags get overridden after load
and response:
{
name: 'test',
tags: [
{name: 'tag1'},
{name: 'tag2'}
]
}
Anyone know how to fix this?
One more question. Is there a way to check if model is loaded or not. Yes, I know that we can add callback to the fetch method, but what about something like this model.isLoaded or model.isPending?
Thanks!
"when I try to load single model I get my property being overridden with plain Javascript array"
You can override the Model#parse method to keep your collection getting overwritten:
parse: function(attrs) {
//reset the collection property with the new
//tags you received from the server
var collection = this.get('tags');
collection.reset(attrs.tags);
//replace the raw array with the collection
attrs.tags = collection;
return attrs;
}
"Is there a way to check if model is loaded or not?"
You could compare the model to its defaults. If the model is at its default state (save for its id), it's not loaded. If it doesn't, it's loaded:
isLoaded: function() {
var defaults = _.result(this, 'defaults');
var current = _.wíthout(this.toJSON(), 'id');
//you need to convert the tags to an array so its is comparable
//with the default array. This could also be done by overriding
//Model#toJSON
current.tags = current.tags.toJSON();
return _.isEqual(current, defaults);
}
Alternatively you can hook into the request, sync and error events to keep track of the model syncing state:
initialize: function() {
var self = this;
//pending when a request is started
this.on('request', function() {
self.isPending = true;
self.isLoaded = false;
});
//loaded when a request finishes
this.on('sync', function() {
self.isPending = false;
self.isLoaded = true;
});
//neither pending nor loaded when a request errors
this.on('error', function() {
self.isPending = false;
self.isLoaded = false;
});
}

Nested backbone model results in infinite recursion when saving

This problem just seemed to appear while I updated to Backbone 1.1. I have a nested Backbone model:
var ProblemSet = Backbone.Model.extend({
defaults: {
name: "",
open_date: "",
due_date: ""},
parse: function (response) {
response.name = response.set_id;
response.problems = new ProblemList(response.problems);
return response;
}
});
var ProblemList = Backbone.Collection.extend({
model: Problem
});
I initially load in a ProblemSetList, which is a collection of ProblemSet models in my page. Any changes to the open_date or due_date fields of any ProblemSet, first go to the server and update that property, then returns. This fires another change event on the ProblemSet.
It appears that all subsequent returns from the server fires another change event and the changed attribute is the "problems" attribute. This results in infinite recursive calls.
The problem appears to come from the part of set method of Backbone.Model (code listed here from line 339)
// For each `set` attribute, update or delete the current value.
for (attr in attrs) {
val = attrs[attr];
if (!_.isEqual(current[attr], val)) changes.push(attr);
if (!_.isEqual(prev[attr], val)) {
this.changed[attr] = val;
} else {
delete this.changed[attr];
}
unset ? delete current[attr] : current[attr] = val;
}
// Trigger all relevant attribute changes.
if (!silent) {
if (changes.length) this._pending = true;
for (var i = 0, l = changes.length; i < l; i++) {
this.trigger('change:' + changes[i], this, current[changes[i]], options);
}
}
The comparison on the problems attribute returns false from _.isEqual() and therefore fires a change event.
My question is: is this the right way to do a nested Backbone model? I had something similar working in Backbone 1.1. Other thoughts about how to proceed to avoid this issue?
You reinstantiate your problems attribute each time your model.fetch completes, the objects are different and thus trigger a new cycle.
What I usually do to handle nested models:
use a model property outside of the attributes handled by Backbone,
instantiate it in the initialize function,
set or reset this object in the parent parse function and return a response omitting the set data
Something like this:
var ProblemSet = Backbone.Model.extend({
defaults: {
name: "",
open_date: "",
due_date: ""
},
initialize: function (opts) {
var pbs = (opts && opts.problems) ? opts.problems : [];
this.problems = new ProblemList(pbs);
},
parse: function (response) {
response.name = response.set_id;
if (response.problems)
this.problems.set(response.problems);
return _.omit(response, 'problems');
}
});
parse gets called on fetch and save (according to backbone documentation), this might cause your infinite loop. I don't think that the parse function is the right place to create the new ProblemsList sub-collection, do it in the initialize function of your model instead.

Initializing nested collections with Backbone

I am trying to nest a Collection View into a Model View.
In order to do so, I used Backbone's Marionnette Composite View and followed that tutorial
At the end he initializes the nested collection view like this:
MyApp.addInitializer(function(options){
var heroes = new Heroes(options.heroes);
// each hero's villains must be a backbone collection
// we initialize them here
heroes.each(function(hero){
var villains = hero.get('villains');
var villainCollection = new Villains(villains);
hero.set('villains', villainCollection);
});
// edited for brevity
});
How would you go doing the same without using the addInitalizer from Marionette?
In my project I am fectching data from the server. And when I try doing something like:
App.candidatures = new App.Collections.Candidatures;
App.candidatures.fetch({reset: true}).done(function() {
App.candidatures.each(function(candidature) {
var contacts = candidature.get('contacts');
var contactCollection = new App.Collections.Contacts(contacts);
candidature.set('contacts', contactCollection);
});
new App.Views.App({collection: App.candidatures});
});
I get an "indefined options" coming from the collection:
App.Collections.Contacts = Backbone.Collection.extend({
model: App.Models.Contact,
initialize:function(models, options) {
this.candidature = options.candidature;
},
url:function() {
return this.candidature.url() + "/contacts";
}
)};
That's because when you're creating the contactCollection, you're not providing a candidatures collections in an options object. You do need to modify your contact collection initialization code to something like:
initialize:function(models, options) {
this.candidature = options && options.candidature;
}
That way the candidature attribute will be set to the provided value (and if not provided, it will be undefined).
Then, you still need to provide the info when you're instanciating the collection:
App.candidatures.each(function(candidature) {
var contacts = candidature.get('contacts');
var contactCollection = new App.Collections.Contacts(contacts, {
candidature: candidature
});
candidature.set('contacts', contactCollection);
});
P.S.: I hope you found my blog post useful!

Multiple collections tied to one base collection with filters and eventing

I have a complex model served from my back end, which has a bunch of regular attributes, some nested models, and a couple of collections.
My page has two tables, one for invalid items, and one for valid items. The items in question are from one of the nested collections. Let's call it baseModel.documentCollection, implementing DocumentsCollection.
I don't want any filtration code in my Marionette.CompositeViews, so what I've done is the following (note, duplicated for the 'valid' case):
var invalidDocsCollection = new DocumentsCollection(
baseModel.documentCollection.filter(function(item) {
return !item.isValidItem();
})
);
var invalidTableView = new BookIn.PendingBookInRequestItemsCollectionView({
collection: app.collections.invalidDocsCollection
});
layout.invalidDocsRegion.show(invalidTableView);
This is fine for actually populating two tables independently, from one base collection. But I'm not getting the whole event pipeline down to the base collection, obviously. This means when a document's validity is changed, there's no neat way of it shifting to the other collection, therefore the other view.
What I'm after is a nice way of having a base collection that I can have filter collections sit on top of. Any suggestions?
I fleshed out my previous attempt and have come up with an extension to Backbone.Collection that does what I need.
collections.FilteredCollection = Backbone.Collection.extend({
initialize: function(items, options) {
if (_.isUndefined(options.baseCollection))
throw "No base collection to watch";
if (!_.isFunction(options.filterFunc)) {
throw "No filter to apply";
}
_.extend(this, options);
this.listenTo(this.baseCollection, 'all', this.reraise);
},
reraise: function (event) {
this.reset(this.baseCollection.filter(this.filterFunc), { silent: true });
var args = [].slice.call(arguments, 1);
this.trigger(event, args);
}
});
The one small issue I have with this is that I have to manually apply filterFunc to the baseCollection, then pass that in as the items parameter when instantiating a FilteredCollection, but that's something I can live with.
The below code is what I'm using to instantiate. Note that there's another almost-exact copy which is for the collection of ONLY VALID items, but any filters can be applied.
var allDocs = theModel.get('Documents');
var invalidOptions = {
baseCollection: allDocs,
filterFunc: function(item) {
return !item.isValidItem();
}
};
var invalidDocs = allDocs.filter(invalidOptions.filterFunc);
var invalidDocsCollection = new collections.FilteredCollection(
invalidDocs, invalidOptions
);

Backbone.js Collection model value not used

Backbone is not using the model specified for the collection. I must be missing something.
App.Models.Folder = Backbone.Model.extend({
initialize: function() {
_.extend(this, Backbone.Events);
this.url = "/folders";
this.items = new App.Collections.FolderItems();
this.items.url = '/folders/' + this.id + '/items';
},
get_item: function(id) {
return this.items.get(id);
}
});
App.Collections.FolderItems = Backbone.Collection.extend({
model: App.Models.FolderItem
});
App.Models.FolderItem = Backbone.Model.extend({
initialize: function() {
console.log("FOLDER ITEM INIT");
}
});
var folder = new App.Models.Folder({id:id})
folder.fetch();
// later on change event in a view
folder.items.fetch();
The folder is loaded, the items are then loaded, but they are not FolderItem objects and FOLDER ITEM INIT is never called. They are basic Model objects.
What did I miss? Should I do this differently?
EDIT:
Not sure why this works vs the documentation, but the following works. Backbone 5.3
App.Collections.FolderItems = Backbone.Collection.extend({
model: function(attributes) {
return new App.Models.FolderItem(attributes);
}
});
the problem is order of declaration for your model vs collection. basically, you need to define the model first.
App.Models.FolderItem = Backbone.Model.extend({...});
App.Collections.FolderItems = Backbone.Collection.extend({
model: App.Models.FolderItem
});
the reason is that backbone objects are defined with object literal syntax, which means they are evaluated immediately upon definition.
this code is functionality the same, but illustrates the object literal nature:
var folderItemDef = { ... };
var folderItemsDef = {
model: App.Models.FolderItem
}
App.Models.FolderItem = Backbone.Model.extend(folderItemDef);
App.Collections.FolderItems = Backbone.Collection.extend(folderItemsDef);
you can see in this example that folderItemDef and folderItems Def are both object literals, which have their key: value pairs evaluated immediately upon definition of the literal.
in your original code, you defined the collection first. this means App.Models.FolderItem is undefined when the collection is defined. so you are essentially doing this:
App.Collection.extend({
model: undefined
});
By moving the model definition above the collection definition, though, the collection will be able to find the model and it will be associated correctly.
FWIW: the reason your function version of setting the collection's model works, is that the function is not evaluated until the app is executed and a model is loaded into the collection. at that point, the javascript interpreter has already found the model's definition and it loads it correctly.

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