join_constraints

# File activerecord/lib/active_record/associations/join_dependency/join_association.rb, line 24
        def join_constraints(foreign_table, foreign_klass, node, join_type, tables, scope_chain, chain)
          joins         = []
          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

            case reflection.source_macro
            when :belongs_to
              key         = reflection.association_primary_key
              foreign_key = reflection.foreign_key
            else
              key         = reflection.foreign_key
              foreign_key = reflection.active_record_primary_key
            end

            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 reflection.type
              constraint = constraint.and table[reflection.type].eq foreign_klass.base_class.name
            end

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

          joins
        end