Backbone.js - id vs idAttribute vs cid

Question

I've been studying Backbone.js for a few weeks, and I feel comfortable using views with models, routers, and collections.

I still have some big gaps:

1. What is the connection between id, cid, and idAttribute? How do they affect each other?

2. When exactly does a new model get its ID? Is the server responsible for assigning it? Do I need to add it to the defaults of the model (maybe as a function)? Maybe the addNewModel function should do that?

Answer 1

What is the connection between id, cid, and idAttribute? How do they affect each other?

Both the cid and id should be unique id's for the model, and can be used to retrieve a model from a collection.

The difference between the two is that the cid is assigned by backbone.js client side and is useful if you don't have an actual id, either because the model hasn't been saved yet to the server or perhaps you aren't even saving it to a db (maybe you're using localStorage). The id attribute should be the id of the model that comes from your server (that is what the id is in your db). idAttribute tells backbone which "field" coming from your server it should use to update the id attribute, by default this is set to "id" but as it says in the documentation if your server uses something else you can set it to that (the example given is setting it to "_id".

When exactly does a new model get its ID? Is the server responsible for assigning it? Do I need to add it to the defaults of the model (maybe as a function)? Maybe the addNewModel function should do that?

They should get the new id's when saved to the server and you shouldn't need to set it manually (based on the idattribute) unless you need more control over the process.