association_join

# File activerecord/lib/active_record/associations.rb, line 1804
            def association_join
              connection = reflection.active_record.connection
              join = case reflection.macro
                when :has_and_belongs_to_many
                  " #{join_type} %s ON %s.%s = %s.%s " % [
                     table_alias_for(options[:join_table], aliased_join_table_name),
                     connection.quote_table_name(aliased_join_table_name),
                     options[:foreign_key] || reflection.active_record.to_s.foreign_key,
                     connection.quote_table_name(parent.aliased_table_name),
                     reflection.active_record.primary_key] +
                  " #{join_type} %s ON %s.%s = %s.%s " % [
                     table_name_and_alias,
                     connection.quote_table_name(aliased_table_name),
                     klass.primary_key,
                     connection.quote_table_name(aliased_join_table_name),
                     options[:association_foreign_key] || klass.to_s.foreign_key
                     ]
                when :has_many, :has_one
                  case
                    when reflection.macro == :has_many && reflection.options[:through]
                      through_conditions = through_reflection.options[:conditions] ? "AND #{interpolate_sql(sanitize_sql(through_reflection.options[:conditions]))}" : ''

                      jt_foreign_key = jt_as_extra = jt_source_extra = jt_sti_extra = nil
                      first_key = second_key = as_extra = nil

                      if through_reflection.options[:as] # has_many :through against a polymorphic join
                        jt_foreign_key = through_reflection.options[:as].to_s + '_id'
                        jt_as_extra = " AND %s.%s = %s" % [
                          connection.quote_table_name(aliased_join_table_name),
                          connection.quote_column_name(through_reflection.options[:as].to_s + '_type'),
                          klass.quote_value(parent.active_record.base_class.name)
                        ]
                      else
                        jt_foreign_key = through_reflection.primary_key_name
                      end

                      case source_reflection.macro
                      when :has_many
                        if source_reflection.options[:as]
                          first_key   = "#{source_reflection.options[:as]}_id"
                          second_key  = options[:foreign_key] || primary_key
                          as_extra    = " AND %s.%s = %s" % [
                            connection.quote_table_name(aliased_table_name),
                            connection.quote_column_name("#{source_reflection.options[:as]}_type"),
                            klass.quote_value(source_reflection.active_record.base_class.name)
                          ]
                        else
                          first_key   = through_reflection.klass.base_class.to_s.foreign_key
                          second_key  = options[:foreign_key] || primary_key
                        end

                        unless through_reflection.klass.descends_from_active_record?
                          jt_sti_extra = " AND %s.%s = %s" % [
                            connection.quote_table_name(aliased_join_table_name),
                            connection.quote_column_name(through_reflection.active_record.inheritance_column),
                            through_reflection.klass.quote_value(through_reflection.klass.name.demodulize)]
                        end
                      when :belongs_to
                        first_key = primary_key
                        if reflection.options[:source_type]
                          second_key = source_reflection.association_foreign_key
                          jt_source_extra = " AND %s.%s = %s" % [
                            connection.quote_table_name(aliased_join_table_name),
                            connection.quote_column_name(reflection.source_reflection.options[:foreign_type]),
                            klass.quote_value(reflection.options[:source_type])
                          ]
                        else
                          second_key = source_reflection.primary_key_name
                        end
                      end

                      " #{join_type} %s ON (%s.%s = %s.%s%s%s%s) " % [
                        table_alias_for(through_reflection.klass.table_name, aliased_join_table_name),
                        connection.quote_table_name(parent.aliased_table_name),
                        connection.quote_column_name(parent.primary_key),
                        connection.quote_table_name(aliased_join_table_name),
                        connection.quote_column_name(jt_foreign_key),
                        jt_as_extra, jt_source_extra, jt_sti_extra
                      ] +
                      " #{join_type} %s ON (%s.%s = %s.%s%s) " % [
                        table_name_and_alias,
                        connection.quote_table_name(aliased_table_name),
                        connection.quote_column_name(first_key),
                        connection.quote_table_name(aliased_join_table_name),
                        connection.quote_column_name(second_key),
                        as_extra
                      ]

                    when reflection.options[:as] && [:has_many, :has_one].include?(reflection.macro)
                      " #{join_type} %s ON %s.%s = %s.%s AND %s.%s = %s" % [
                        table_name_and_alias,
                        connection.quote_table_name(aliased_table_name),
                        "#{reflection.options[:as]}_id",
                        connection.quote_table_name(parent.aliased_table_name),
                        parent.primary_key,
                        connection.quote_table_name(aliased_table_name),
                        "#{reflection.options[:as]}_type",
                        klass.quote_value(parent.active_record.base_class.name)
                      ]
                    else
                      foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
                      " #{join_type} %s ON %s.%s = %s.%s " % [
                        table_name_and_alias,
                        aliased_table_name,
                        foreign_key,
                        parent.aliased_table_name,
                        parent.primary_key
                      ]
                  end
                when :belongs_to
                  " #{join_type} %s ON %s.%s = %s.%s " % [
                     table_name_and_alias,
                     connection.quote_table_name(aliased_table_name),
                     reflection.klass.primary_key,
                     connection.quote_table_name(parent.aliased_table_name),
                     options[:foreign_key] || reflection.primary_key_name
                    ]
                else
                  ""
              end || ''
              join << %(AND %s.%s = %s ) % [
                connection.quote_table_name(aliased_table_name),
                connection.quote_column_name(klass.inheritance_column),
                klass.quote_value(klass.name.demodulize)] unless klass.descends_from_active_record?

              [through_reflection, reflection].each do |ref|
                join << "AND #{interpolate_sql(sanitize_sql(ref.options[:conditions]))} " if ref && ref.options[:conditions]
              end

              join
            end