Brandon Harris

JSON Templates in Rails

Sometimes, you just don't want to do call the "to_json" message on an object. It could be that the object has a lot of attributes, the json needs are very simple, or you simply don't like the default structure.

Fortunately, there is a very easy solution: JSON templates. This is built in, and you might have not even known it.

In my case, I wanted to plot a bunch of people and their locations on a map. I had the following model:

1 class Person < ActiveRecord::Base
2   # ...
3 
4   def geo_location
5     [latitude,longitude].compact.join(",")
6   end
7 
8   # ...
9 end

I have the following controller:

1 class PeopleController < ApplicationController
2   respond_to :html, :json
3 
4   def index
5    @people = Person.find(:all)
6    respond_with(@people)
7   end
8   # ...
9 end

Now, create index.json.erb. I tried doing this with haml, but I really didn't like the way I had to handle the necessary whitespace. Your call if you want to use it.

1 [
2 <%- @people.each do |p| %>
3   {
4     "id": "<%=p.id %>",
5     "location": "<%= p.location %>"
6   },
7 <% end %>
8 {}]

There is a wart, the trailing {}. I didn't want to include any logic, as it would slow down this rather large dataset. The whole reason I am doing it this way is for speed. I have no need to display all the attribute data from the "people" table, I just need to plot a heat map. Suggestions are welcome, the side effect is that the last point that is attempted to be plotted, is ignored.