Backbone.js系列

Question

i'm a beginner to backbone.js

why would you want to use a COLLECTION?

Can't you just have a view associated with each model?

Also, does an event bond to a collection of model apply to all models?

Answer 1

When you are operating on large datasets it is very much necessary to have a mechanism to perform operations on whole datasets or subsets. In Backbone.js Collection class provides this mechanism. A few very frequent usages of Collection may be outlined as follows:

• Suppose you are fetching the results of a query from a database. Now you can create a model corresponding to the structure of record, define a collection, create a collection instance, define the url (and if required customize the ajax request) and then give a call to fetch. This is more advantageous to having an array of models: firstly it is more convenient than to iterate through the parsed json data structure and create a model from each record object. Secondly the entire collection can be updated at once to the server. As pointed out by Mario, it makes working with related records very convenient.

• Secondly, Collection class provides you a base class which you can easily auxiliate with your functions to provide custom filtering and sorting capabilities.

• You can have Views eg. data grids, trees etc to represent the collection. It is convenient to code and also think in terms of a view representing a collection.

Answer 2

You use them when you have nested models, see http://documentcloud.github.com/backbone/#FAQ-nested

I guess you could have a view associated with each model but not necessarily. Not sure about the last part, maybe run a quick test.

Answer 3

You could use a collection is to represent a one-to-many relationship. This is type of thing is perfect when your backend datastore is a document database (having embedded documents).

You can also use a collection to allow for iteration over your models.

Since a model can only belong to a single collection it almost makes sense at times to treat a collection like a table in the database. In the database I have a people table. In my javascript I have a people collection.

(The reason a model can only belong to a single collection is that upon adding a model to a collection the collection stores a reference to itself directly on the model. Adding a model to a second collection would overwrite the model's reference to the first collection.)