Use count instead of select/reject RB-PR1006
Performance
Major
Usages of count on an Enumerable that follow calls to select or reject can be made more efficient. Querying logic can instead be passed to the count call.
ActiveRecord compatibility: ActiveRecord will ignore the block that is passed to count. Other methods, such as select, will convert the association to an array and then run the block on the array. A simple workaround to make count work with a block is to call to_a.count {...}.
Example:
Model.where(id: [1, 2, 3]).select { |m| m.method == true }.size
becomes:
Model.where(id: [1, 2, 3]).to_a.count { |m| m.method == true }
Bad practice
[1, 2, 3].select { |e| e > 2 }.size
[1, 2, 3].reject { |e| e > 2 }.size
[1, 2, 3].select { |e| e > 2 }.length
[1, 2, 3].reject { |e| e > 2 }.length
[1, 2, 3].select { |e| e > 2 }.count { |e| e.odd? }
[1, 2, 3].reject { |e| e > 2 }.count { |e| e.even? }
array.select(&:value).count
Recommended
[1, 2, 3].count { |e| e > 2 }
[1, 2, 3].count { |e| e < 2 }
[1, 2, 3].count { |e| e > 2 && e.odd? }
[1, 2, 3].count { |e| e < 2 && e.even? }
Model.select('field AS field_one').count
Model.select(:value).count