Question

I am creating a instance variable that gets passed to my view. This variable ‘post’ has a user_id associated with it and I wanted to add an extra attribute called ‘username’ so I can also pass that and use it in the view.

Here is an example of what I would like to do.

@post = Post.find(params[:id])
@post.username = User.find(@post.user_id).username

A username column does exist on my Users model but not my Songs model. So it won’t let me use

@post.username

I know I can just make an entirely new instance variable and put that information in there but I would like to keep everything nice and neat, in one variable. Which will also make my json rendered code look cleaner.

Any ideas on how I can accomplish this?

Thanks!

Answer 1

Based on the presence of a user_id in your Post model, you probably already have an association set up that can retrieve the username. It will probably save a lot of trouble to simply use the existing association:

@post = Post.find(params[:id])
username = @post.user.username

If you’re likely to be querying more than one post at a time (e.g., on an index page, calling .includes to tell Rails to eager-load an association will help you avoid the N+1 problem:

@posts = Post.includes(:user).all

Finally, to include the associated record in your JSON output, pass the :include parameter as you serialize:

# in controller
render :json => @post.to_json(:include => :user)

This question includes a much more comprehensive discussion of serialization options. Well worth a read.