How can I count the result of an ActiveRecord .group query? Chaining .count returns a hash

Question

I can use the following :

User.where("zip_code = '48104'").group('users.id').count

To get hashes like :

{195=>1, 106=>1, 120=>1, 227=>1, 247=>1, 264=>1, 410=>1}

Is there a way I can count these hashes, and just return 7, instead of the above result ?

I know this doesn't make sense in the above scenario, and I can just do it by not using the group clause. But I'm working on a more complex query, where I need to implement this. Thanks in advance.

Answer 1

Try:

User.where("zip_code = '48104'").group('users.id').count.length

Answer 2

The accepted answer is not scalable. Using @robbrit's method on a query with 25,000 matching users would pull 25,000 results (ie an array with 25,000 elements) into memory and then count the elements array. Here is a method that will do it without pulling all that data:

def count_query(query)
  query = "SELECT count(*) AS count_all FROM (#{query.to_sql}) x"
  ActiveRecord::Base.connection.execute(query).first.try(:[], 0).to_i
end

It is used like this:

query = User.where("zip_code = '48104'").group('users.id')
count = count_query(query)

This works for me using mysql, btw.

It was inspired by this guy: https://github.com/mrbrdo/active_record_group_count/blob/master/lib/active_record_group_count/scope.rb