Adding variable to make dynamic Ruby statement

Question

I am having trouble creating a dynamic statement in a Rails ERB template. This is essentially what I'm trying to do:

<%= photo.@photo_col.url %>

This will make the statement dynamic based on this condition in the controller:

if !params[:cat]
    @my_photos = BusinessPhoto.where(contributor_id: session[:user_id])
    @photo_col = "business_photo"
elsif params[:cat] && params[:cat] == "event"
    @my_photos = EventPhoto.where(contributor_id: session[:user_id])
    @photo_col = "event_photo"
elsif params[:cat] && params[:cat] == "blog"
    @my_photos = BlogPhoto.where(contributor_id: session[:user_id])
    @photo_col = "post_photo"
end

Can anyone see a problem with this statement?

You could remove params[:cat] && without breaking anything. It has no practical effect here. — Henrik N
– Henrik N, Commented Dec 9, 2014 at 19:07
Tweaked the code further for fun, if you're interested: gist.github.com/henrik/55066739a6e2147168a3 — Henrik N
– Henrik N, Commented Dec 9, 2014 at 19:14

Uri Agassi · Accepted Answer · 2014-12-09 18:56:41Z

2

I'm not sure what photo is, so there might be a more straight forward way, but what you are trying to do is call a method by its name dynamically. You do that using public_send:

<%= photo.public_send(@photo_col).url %>

answered Dec 9, 2014 at 18:56

Uri Agassi

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3 Comments

Arun Over a year ago

Beautiful, thank you! I knew it had to be something simple :)

Henrik N Over a year ago

Just be careful that the user can't set the @photo_col freely (i.e. never do @photo_col = params[:col]). If a user would pass in the column name "destroy", for example, they would cause the photo to be removed from the database :)

Uri Agassi Over a year ago

@Arun - if photo is an ActiveRecord, you might want to try photo[@photo_col].url instead

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