join_constraints

# File activerecord/lib/active_record/associations/join_dependency/join_association.rb, line 26
        def join_constraints(foreign_table, foreign_klass, node, join_type, tables, scope_chain, chain)
          joins         = []
          bind_values   = []
          tables        = tables.reverse

          scope_chain_index = 0
          scope_chain = scope_chain.reverse

          # The chain starts with the target table, but we want to end with it here (makes
          # more sense in this context), so we reverse
          chain.reverse_each do |reflection|
            table = tables.shift
            klass = reflection.klass

            join_keys   = reflection.join_keys(klass)
            key         = join_keys.key
            foreign_key = join_keys.foreign_key

            constraint = build_constraint(klass, table, key, foreign_table, foreign_key)

            scope_chain_items = scope_chain[scope_chain_index].map do |item|
              if item.is_a?(Relation)
                item
              else
                ActiveRecord::Relation.create(klass, table).instance_exec(node, &item)
              end
            end
            scope_chain_index += 1

            scope_chain_items.concat [klass.send(:build_default_scope, ActiveRecord::Relation.create(klass, table))].compact

            rel = scope_chain_items.inject(scope_chain_items.shift) do |left, right|
              left.merge right
            end

            if rel && !rel.arel.constraints.empty?
              bind_values.concat rel.bind_values
              constraint = constraint.and rel.arel.constraints
            end

            if reflection.type
              value = foreign_klass.base_class.name
              column = klass.columns_hash[reflection.type.to_s]

              substitute = klass.connection.substitute_at(column)
              bind_values.push [column, value]
              constraint = constraint.and table[reflection.type].eq substitute
            end

            joins << table.create_join(table, table.create_on(constraint), join_type)

            # The current table in this iteration becomes the foreign table in the next
            foreign_table, foreign_klass = table, klass
          end

          JoinInformation.new joins, bind_values
        end