Add Example use cases with verify_sql in README

README.md

@@ -20,7 +20,9 @@
     * [Exclude dynamically changed values from json](#exclude-dynamically-changed-values-from-json)
     * [Approving a spec](#approving-a-spec)
     * [Expensive computations](#expensive-computations)
-    * [RSpec executable](#rspec-executable)<!-- endToc -->
+    * [RSpec executable](#rspec-executable)
+  * [Example use cases](#example-use-cases)
+    * [Verifying complex SQL in Rails](#verifying-complex-sql-in-rails)<!-- endToc -->
 
 Approvals are based on the idea of the *_golden master_*.
 
@@ -284,4 +286,48 @@ verify do
 end
 ```
 
+## Example use cases
+
+### Verifying complex SQL in Rails
+
+If you're using Rails and want to avoid accidentally introducing N+1 database queries, you can define a `verify_sql` helper like so:
+
+```ruby
+# spec/spec_helper.rb
+
+require "./spec/support/approvals_helper"
+
+RSpec.configure do |config|
+  config.include ApprovalsHelper
+end
+
+# spec/support/approvals_helper.rb
+
+module ApprovalsHelper
+  def verify_sql(&block)
+    sql = []
+
+    subscriber = ->(_name, _start, _finish, _id, payload) do
+      sql << payload[:sql].split("/*").first.gsub(/\d+/, "?")
+    end
+
+    ActiveSupport::Notifications.subscribed(subscriber, "sql.active_record", &block)
+
+    verify :format => :txt do
+      sql.join("\n") + "\n"
+    end
+  end
+end
+
+# spec/models/example_spec.rb
+
+it "is an example spec" do
+   verify_sql do
+     expect(Thing.complex_query).to eq(expected_things)
+   end
+ end
+```
+
+This `verify_sql` can be useful in model or integration tests; anywhere you're worried about the SQL being generated by complex queries, API endpoints, GraphQL fields, etc.
+
 Copyright (c) 2011 Katrina Owen, released under the MIT license