Counting the number of queries performed
Here's another formulation of Ryan's and Yuriy's solution that's just a function you add to your test_helper.rb
:
def count_queries &block
count = 0
counter_f = ->(name, started, finished, unique_id, payload) {
unless payload[:name].in? %w[ CACHE SCHEMA ]
count += 1
end
}
ActiveSupport::Notifications.subscribed(counter_f, "sql.active_record", &block)
count
end
Usage is just:
c = count_queries do
SomeModel.first
end
- helpful error message
- removes subscribers after execution
(based on Jaime Cham's answer)
class ActiveSupport::TestCase
def sql_queries(&block)
queries = []
counter = ->(*, payload) {
queries << payload.fetch(:sql) unless ["CACHE", "SCHEMA"].include?(payload.fetch(:name))
}
ActiveSupport::Notifications.subscribed(counter, "sql.active_record", &block)
queries
end
def assert_sql_queries(expected, &block)
queries = sql_queries(&block)
queries.count.must_equal(
expected,
"Expected #{expected} queries, but found #{queries.count}:\n#{queries.join("\n")}"
)
end
end
I think you answered your own question by mentioning assert_queries
, but here goes:
I would recommend taking a look at the code behind assert_queries
and using that to build your own method which you can use to count queries. The main magic involved here is this line:
ActiveSupport::Notifications.subscribe('sql.active_record', SQLCounter.new)
I had a bit of a tinker this morning and ripped out the parts of ActiveRecord that do the query counting and came up with this:
module ActiveRecord
class QueryCounter
cattr_accessor :query_count do
0
end
IGNORED_SQL = [/^PRAGMA (?!(table_info))/, /^SELECT currval/, /^SELECT CAST/, /^SELECT @@IDENTITY/, /^SELECT @@ROWCOUNT/, /^SAVEPOINT/, /^ROLLBACK TO SAVEPOINT/, /^RELEASE SAVEPOINT/, /^SHOW max_identifier_length/]
def call(name, start, finish, message_id, values)
# FIXME: this seems bad. we should probably have a better way to indicate
# the query was cached
unless 'CACHE' == values[:name]
self.class.query_count += 1 unless IGNORED_SQL.any? { |r| values[:sql] =~ r }
end
end
end
end
ActiveSupport::Notifications.subscribe('sql.active_record', ActiveRecord::QueryCounter.new)
module ActiveRecord
class Base
def self.count_queries(&block)
ActiveRecord::QueryCounter.query_count = 0
yield
ActiveRecord::QueryCounter.query_count
end
end
end
You will be able to reference the ActiveRecord::Base.count_queries
method anywhere. Pass it a block wherein your queries are run and it will return the number of queries that have been executed:
ActiveRecord::Base.count_queries do
Ticket.first
end
Returns "1" for me. To make this work: put it in a file at lib/active_record/query_counter.rb
and require it in your config/application.rb
file like this:
require 'active_record/query_counter'
Hey presto!
A little bit of explanation probably is required. When we call this line:
ActiveSupport::Notifications.subscribe('sql.active_record', ActiveRecord::QueryCounter.new)
We hook into Rails 3's little notifications framework. It's a shiny little addition to the latest major version of Rails that nobody really knows about. It allows us to subscribe to notifications of events within Rails by using the subscribe
method. We pass in the event we want to subscribe to as the first argument then any object that responds to call
as the second.
In this case when a query is executed our little query counter will dutifully increment the ActiveRecord::QueryCounter.query_count variable, but only for the real queries.
Anyway, this was fun. I hope it comes useful to you.
My vision of Ryan's script (cleaned up a bit and wrapped in a matcher), hope it is still actual for someone:
I put this to spec/support/query_counter.rb
module ActiveRecord
class QueryCounter
attr_reader :query_count
def initialize
@query_count = 0
end
def to_proc
lambda(&method(:callback))
end
def callback(name, start, finish, message_id, values)
@query_count += 1 unless %w(CACHE SCHEMA).include?(values[:name])
end
end
end
and this to spec/support/matchers/exceed_query_limit.rb
RSpec::Matchers.define :exceed_query_limit do |expected|
match do |block|
query_count(&block) > expected
end
failure_message_for_should_not do |actual|
"Expected to run maximum #{expected} queries, got #{@counter.query_count}"
end
def query_count(&block)
@counter = ActiveRecord::QueryCounter.new
ActiveSupport::Notifications.subscribed(@counter.to_proc, 'sql.active_record', &block)
@counter.query_count
end
end
Usage:
expect { MyModel.do_the_queries }.to_not exceed_query_limit(2)