In Rails, what is the best way to update a record or create a new one if it doesn't exist?

Question

I have a create statement for some models, but it’s creating a record within a join table regardless of whether the record already exists.

Here is what my code looks like:

@user = User.find(current_user) @event = Event.find(params[:id]) for interest in @event.interests  @user.choices.create(:interest => interest, :score => 4) end 

The problem is that it creates records no matter what. I would like it to create a record only if no record already exists; if a record does exist, I would like it to take the attribute of the found record and add or subtract 1.

I’ve been looking around have seen something called find_or_create_by. What does this do when it finds a record? I would like it to take the current :score attribute and add 1.

Is it possible to find or create by id? I’m not sure what attribute I would find by, since the model I’m looking at is a join model which only has id foreign keys and the score attribute.

I tried

@user.choices.find_or_create_by_user(:user => @user.id, :interest => interest, :score => 4) 

but got

undefined method find_by_user

What should I do?

Answer 1

my_class = ClassName.find_or_initialize_by_name(name)  my_class.update_attributes({    :street_address => self.street_address,    :city_name => self.city_name,    :zip_code => self.zip_code }) 

Answer 2

Assuming that the Choice model has a user_id (to associate with a user) and an interest_id (to associate with an interest), something like this should do the trick:

@user = User.find(current_user) @event = Event.find(params[:id])  @event.interests.each do |interest|   choice = @user.choices.find_or_initialize_by_interest_id(interest.id) do |c|     c.score = 0 # Or whatever you want the initial value to be - 1   end    choice.score += 1   choice.save! end 

Some notes:

1. You don't need to include the user_id column in the find_or_*_by_*, as you've already instructed Rails to only fetch choices belonging to @user.
2. I'm using find_or_initialize_by_*, which is essentially the same as find_or_create_by_*, with the one key difference being that initialize doesn't actually create the record. This would be similar to Model.new as opposed to Model.create.
3. The block that sets c.score = 0 is only executed if the record does not exist.
4. choice.score += 1 will update the score value for the record, regardless if it exists or not. Hence, the default score c.score = 0 should be the initial value minus one.
5. Finally, choice.save! will either update the record (if it already existed) or create the initiated record (if it didn't).