Why no error message when trying to add a model to the same collection twice?

[alexgoldstone]

0.9.1 just threw a "Can't add the same model to a collection twice" error. This helped me identify and resolve a serious server-side bug that might have gone unnoticed for some time if the client-side error had not been thrown.

I see that duplicates are ignored silently as of 0.9.2 and this was clearly a conscious decision so I just wondered what the motivation for this was.

I can't think of a reason (other than a bug) for trying to add a duplicate model to a collection that can't support duplicates and I would therefore expect to see an error message even if the code is able to mitigate the error as 0.9.2 does.

[jashkenas]

For a long time -- our position and reasoning was along the same lines as yours: Duplicate models in a collection indicate an application logic error, and should be warned early.

But there are a number of folks who appreciate "sloppy" adds, where you can just keep trying to add models to a collection without checking if they're in there first -- so we made the change to be more forgiving.

Feel free to override your copy of Backbone.Collection.prototype.add with an early check and error if you like.