merge_joins

# File activerecord/lib/active_record/relation/merger.rb, line 107
        def merge_joins
          return if other.joins_values.blank?

          if other.klass == relation.klass
            relation.joins!(*other.joins_values)
          else
            joins_dependency, rest = other.joins_values.partition do |join|
              case join
              when Hash, Symbol, Array
                true
              else
                false
              end
            end

            join_dependency = ActiveRecord::Associations::JoinDependency.new(other.klass,
                                                                             joins_dependency,
                                                                             [])
            relation.joins! rest

            @relation = relation.joins join_dependency
          end
        end