Adding a parameter to an instance variable in Rails

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!

Community · Accepted Answer · 2017-05-23 12:11:25Z

4

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.

edited May 23, 2017 at 12:11

CommunityBot

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answered Mar 17, 2012 at 20:29

rjz

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3 Comments

Dan Over a year ago

thanks, I had no idea about this association. Is there anyway to add the username information to the json output for the page?

Bradley Priest Over a year ago

That's a separate issue, how are you rendering it to JSON? If you are using the defaults then pass options into the to_json call. E.g. render :json => @post.to_json(:include => :user). Or if you want the Post JSON object to have the username everywhere in your app then customize the as_json method in the Post model.

Dan Over a year ago

awesome thanks! that's exactly what I needed. I'm using the @post.user.username association in my views and added the json code to get the user in my controller. Thanks again for the quick replies.

asitmoharna · Accepted Answer · 2012-03-17 20:34:19Z

2

No need to pass a separate instance variable. 1. You can use @post.user.username in view itself. 2. Or you can create a helper and pass @post.user

def username user
 user.username
end

answered Mar 17, 2012 at 20:34

asitmoharna

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3 Comments

Dan Over a year ago

Ya @post.user.username worked just fine. However my json output still has user_id = # is there anyway I can also add the username to the json output for the page?

asitmoharna Over a year ago

You need to add user while rendering json as @post.to_json(:include => :user)

Dan Over a year ago

thanks asitmoharna this solution worked. thanks for the quick reply

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