Created
April 13, 2023 20:47
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A custom rspec matcher to catch n+1 queries
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| # use this matched to catch most n+1 queries in request specs by creating at least three records, then | |
| # doing something like expect { subject }.to not_execute_n_plus_one | |
| RSpec::Matchers.define :not_execute_n_plus_one do | |
| match do |block| | |
| @queries = [] | |
| ActiveSupport::Notifications.subscribe 'sql.active_record' do |_, _, _, _, values| | |
| next if %w(CACHE SCHEMA).include? values[:name] | |
| next if values[:sql].start_with?("SAVEPOINT") | |
| next if values[:sql].start_with?("RELEASE SAVEPOINT") | |
| next if values[:sql].start_with?("INSERT INTO") | |
| @queries << values[:sql] | |
| end | |
| block.call | |
| @sqls = @queries.reduce({}) do |acc, q| | |
| acc["\"#{q}\""] ||= 0 | |
| acc["\"#{q}\""] += 1 | |
| acc | |
| end.select { |_k, v| v > 2 } | |
| @sqls.empty? | |
| end | |
| supports_block_expectations | |
| failure_message do |_actual| | |
| sql_messages = @sqls.map do |k, v| | |
| "#{k} (executed #{v} times)" | |
| end | |
| "The following n+1(s) queries were found: \n#{sql_messages.join("\n")}" | |
| end | |
| end |
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