How to fail Ajax request in Rails?

When user clicks a specific item, I use jQuery's post method to update something in the database:

$.post("/posts/" + post_id + "/update_something", 
       { some_param: some_value }, 

where update_something looks like this:

def update_something
  post = Post.find(params[:id])
  post.update_attributes(:some_field => params[:some_param])
  render :nothing => true

The problem is if update_attributes fails, the request still succeeds and success_handler is executed.

How could I cause the request to fail when update_attributes fails such that success_handler won't be executed?


You can either do render :status => 400 (or some other error code) in Rails, which will trigger the error callback of $.ajax(), or you can render some JSON with an error message:

render :json => { :success => false }

Then in your success_handler function you would:

function success_handler (response) {
    if (response.success) {
        // do stuff


Oh, and update_attributes returns false when it fails. So you can render your response based on that.

Edit 2 years later:

After a couple years and seeing that this has a few upvotes, I'd highly recommend using the status: 400 method instead of rendering 200. It's what the error handler in AJAX requests are for, and should be used that way.

Well, you have to add an error handler, and give it an error to handle. So, in your JavaScript:

$.post( "/posts/" + post_id + "/update_something",
        { some_param : some_value }
  .done( successHandler )
  .fail( errorHandler )      // define errorHandler somewhere, obviously

And in Rails:

def update_something
  post    = Post.find params[ :id ]

  success = post.update_attributes :some_field => params[ :some_param ]

  head success ? :ok : :internal_server_error

Note: 500 may or may not be the appropriate error code here—choose whichever among the 400s and 500s is appropriate.

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