Does anyone know of a way to get ActiveRecord to update only the columns which have changed? For example, consider a table foos with columns x,y,z. If I do f = Foo.find(123) f.update_attributes(:x => 99) then I want AR to generate UPDATE foos SET x=99 WHERE id=123 rather than what it currently does: UPDATE foos SET x=99, y=2, z=3 WHERE id=123 (assuming y=2 and z=3 were the values read in by Foo.find) Why do I want this? Well, I have tables which are updated asynchronously due to external events, as well as by the user looking at the record in Rails. Both the frontend and the event-handling backend are using ActiveRecord. There are some fields which are updated by the operator, and others which are updated by the backend. But using ActiveRecord, there's a race condition between reading a row and writing it back out again, which means that changes made by the other party may be lost. I searched for a plugin at http://agilewebdevelopment.com/plugins/search?search=update but couldn't find anything relevant. So, the options I can think of are: (1) Bypass ActiveRecord's 'save' and 'update' methods entirely f = Foo.find(123) ... compare f with params, determine that only 'x' has changed Foo.update_all(['x=?',params[:foo][:x]], ['id=?',123]) But this has to be done consistently everywhere. I guess I can write my own version of update_attributes which does this. (2) Read each record twice: f1 = Foo.find(123) ... compare f1 with params, determine that only 'x' has changed f2 = Foo.find(123, :select => 'x') f2.update_attributes(params[:foo]) This seems like unnecessary overhead. I had a quick look through the code path for 'update_attributes' but it seems to be intimately bound to 'save', and 'save' seems to have no concept of which attributes have changed. Thanks for any suggestions. Regards, Brian.
on 2007-05-01 14:29