Faster Auto-Completion with Rails

Auto-Complete is a great tool when it provides possible results BEFORE you finish typing. Unfortunately, using Rails’s included AJAX helpers to query the database as you type often results in a large delay before matches are returned.

However, there is a lightning-quick option: pre-fetch the results in a Javascript array.

In a client project, users can add labels to events on their calendar. To prevent users from creating variations of the same label name (i.e. – “favorite” vs. “favorites”), we needed to provide faster auto-complete functionality than that available through Rails’s provided AJAX helpers.

We created a simple helper method for this case (special thanks to Chad Fowler and his Rails Recipes book for the inspiration).

Take a look at the local_auto_complete_field helper method. TXT (Editor’s note: this is no longer available.)

To call the function from your views:

<br></br> <%= local_auto_complete_field('name',@labels) %><br></br>

In the above example, we are adding JavaScript-powered auto-complete functionality to the 'name' text field. The JavaScript array is generated by calling #name on each element in the @labels array. To override this behavior:

 <%= local_auto_complete_field('name',@labels,                                :method => 'description') %>

Here’s to faster auto-completion!