Question

I am trying to build an API using Rails that will inspect the request header for "If-Modified-Since" and render only the objects that were modified past that date. The problem is I am stuck trying to obtain the value from the request header in the controller.

# API
def index
   @products = Product.where{updated_at > request.headers["If-Modified-Since"]}
   render "v1/products/index"
end

What is the correct way for extracting values from the request header?

Answer 1

First: If-Modified-Since is for HTTP cache validation. Please don’t use it this way. Use a parameter instead.

To answer your question: request.headers[] is the proper way of accessing request headers. For reference, request is an ActionDispatch::Request object.

The problem here is how you’re trying to express the constraint. You’re passing a block into ActiveRecord‘s #where method, and the block doesn’t make any sense (Symbol#>(String)?). You can express this as a SQL fragment, like:

Product.where("updated_at > ?", params[:last_update])

Alternately, you could drop in Squeel, and write:

Product.where{ updated_at > params[:last_update] }