instance method build_joins

# File activerecord/lib/active_record/relation/query_methods.rb, line 974
    def build_joins(manager, joins)
      buckets = joins.group_by do |join|
        case join
        when String
          :string_join
        when Hash, Symbol, Array
          :association_join
        when ActiveRecord::Associations::JoinDependency
          :stashed_join
        when Arel::Nodes::Join
          :join_node
        else
          raise 'unknown class: %s' % join.class.name
        end
      end

      association_joins         = buckets[:association_join] || []
      stashed_association_joins = buckets[:stashed_join] || []
      join_nodes                = (buckets[:join_node] || []).uniq
      string_joins              = (buckets[:string_join] || []).map(&:strip).uniq

      join_list = join_nodes + custom_join_ast(manager, string_joins)

      join_dependency = ActiveRecord::Associations::JoinDependency.new(
        @klass,
        association_joins,
        join_list
      )

      joins = join_dependency.join_constraints stashed_association_joins

      joins.each { |join| manager.from(join) }

      manager.join_sources.concat(join_list)

      manager
    end