Caching Products

Sometimes caching specific parts of a page can improve performance. Rails simplifies this process with Solid Cache, a database-backed cache store that comes included by default.

Using the cache method, we can store HTML in the cache. Let’s cache the header in app/views/products/show.html.erb.

<% cache @product do %>
  <h1><%= @product.name %></h1>
<% end %>

By passing @product into cache, Rails generates a unique cache key for the product. Active Record objects have a cache_key method that returns a String like "products/1". The cache helper in the views combines this with the template digest to create a unique key for this HTML.

To enable caching in development, run the following command in your terminal.

$ bin/rails dev:cache

When you visit a product’s show action (like /products/2), you’ll see the new caching lines in your Rails server logs:

Read fragment views/products/show:a5a585f985894cd27c8b3d49bb81de3a/products/1-20240918154439539125 (1.6ms)
Write fragment views/products/show:a5a585f985894cd27c8b3d49bb81de3a/products/1-20240918154439539125 (4.0ms)

The first time we open this page, Rails will generate a cache key and ask the cache store if it exists. This is the Read fragment line.

Since this is the first page view, the cache does not exist so the HTML is generated and written to the cache. We can see this as the Write fragment line in the logs.

Refresh the page and you’ll see the logs no longer contain the Write fragment.

Read fragment views/products/show:a5a585f985894cd27c8b3d49bb81de3a/products/1-20240918154439539125 (1.3ms)

The cache entry was written by the last request, so Rails finds the cache entry on the second request. Rails also changes the cache key when records are updated to ensure that it never renders stale cache data.

Learn more in the Caching with Rails guide.