Question

In the example Todos app for backbone.js, this takes place:

clearCompleted: function() {
  _.each(Todos.done(), function(todo){ todo.clear(); });
  return false;
},

This deletes multiple models by sending out multiple http DELETE requests to whatever service is backing the app. In the example’s case that is no problem b/c they are using a local storage solution.

But when I try a similar process with a database on the backend (sqlite/datamapper/sinatra) the fact that it sends off multiple delete http requests simultaneously causes the db to lock and send back an error.

Is this something any of you have run into?

I can think of two ways around it:

1. Have a destroyBatch() that sends an array of id’s into a DELETE call, and have sinatra sniff out the multiple ids and handle the deletes all at once server-side.

2. Have a destroyAsync() on the client-side that pushes the ids into a queue and calls destroy() on the models one-by-one in an async chain reaction until they are all gone ( but you would see them being deleted one by one on the screen with a pause in between each).

Do either of those solutions seem reasonable, or am I a frail goose flapping wildly?

-j

Answer 1

Option 2 is not a viable one. Your user can click back or close the window and the deletion will not succeed completely. So out with this one.

This leaves us to:

• Fix your initial problem of locks in the DB 😀
• Send all ids to be deleted at once.

I would try to solve the initial problem first. What is causing them to lock up? I am pretty sure that in development mode sinatra will process a single request at a time, so sending a bunch of delete will actually be serialized on the backend processing… That is another question altogether that would be linked to the sqlite error returned.

As for sending the deletion in batches. It is a good idea, but it deviates from the standard RESTful controller. So you will have to handle that yourself as backbone do not provide a way to do this. You can add a deleteAll method on the collection and handle the sync from there (do not forget to send events if you are relying on them).