Question

I want to render a list of objects into JSON, but I don’t want to user to_json because I want to render a very specific format and subset of information.

This is my view (foo.json.erb):

{
"id" : <%= @user.id %>,
"progress" : [
    <% @rewards_tapped[0..-2].each do |reward| %>
        <%= render "rewardprogress", :reward => reward, 
                                     :user => @user %>,
    <% end %>
    <%= render "rewardprogress", :reward => @rewards_tapped.last, 
                                 :user => @user %>
]
}

As you can see, it is pretty ugly because I have to render the last item in @rewards_tapped separately so that it does not have a comma after the entry (to make valid JSON).

There has to be a better way to do this, I’m just a bit new to Ruby. Can someone point me in the right direction?

Answer 1

If you don’t require incremental rendering, then you could simply build up a nested hash/array Ruby data structure, and call #to_json on that. You can also use symbols as keys, and they’ll become string keys in the resulting JSON.

Assuming you do need the incremental rendering, then this might be a minor improvement you could make (or might just be replacing one kind of ugly with another). This might be faster though if converting @rewards_tapped to an array for [0..-2] is at all slow.

{
"id" : <%= @user.id %>,
"progress" : [
    <% @rewards_tapped.each_with_index do |reward, idx|
    %><%= idx == 0 ? '' : ',' %>
    <%= render "rewardprogress", :reward => reward, 
                                     :user => @user
    %><% end %>
]
}