Define method on activerecord relation

Question

I want to define a custom method on an activerecord relation, eg:

Transaction.all.summed_values

A simple example would be where summed_values should evaluate sum(:value) on the relation.

Where should I define the method summed_values? Looks like it should be on ActiveRecord::Relation. If it should be directly there, which file should I put it in?

Also, if this new method only has meaning for Transactions, is there any way to tell rails to only define this method for ActiveRecord::Relations that consist of Transactions?

Answer 1

You should use extending

Transaction.all.extending do
  def summed_values
    sum(:what_you_want)
  end
end

For more info: ActiveRecord::QueryMethods