flink-libraries/flink-table/src/main/scala/org/apache/flink/table/descriptors/StreamableDescriptor.scala

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.table.descriptors

/**
  * A trait for descriptors that allow to convert between a dynamic table and an external connector.
  */
trait StreamableDescriptor[D <: StreamableDescriptor[D]] extends TableDescriptor {

  /**
    * Declares how to perform the conversion between a dynamic table and an external connector.
    *
    * In append mode, a dynamic table and an external connector only exchange INSERT messages.
    *
    * @see See also [[inRetractMode()]] and [[inUpsertMode()]].
    */
  def inAppendMode(): D

  /**
    * Declares how to perform the conversion between a dynamic table and an external connector.
    *
    * In retract mode, a dynamic table and an external connector exchange ADD and RETRACT messages.
    *
    * An INSERT change is encoded as an ADD message, a DELETE change as a RETRACT message, and an
    * UPDATE change as a RETRACT message for the updated (previous) row and an ADD message for
    * the updating (new) row.
    *
    * In this mode, a key must not be defined as opposed to upsert mode. However, every update
    * consists of two messages which is less efficient.
    *
    * @see See also [[inAppendMode()]] and [[inUpsertMode()]].
    */
  def inRetractMode(): D

  /**
    * Declares how to perform the conversion between a dynamic table and an external connector.
    *
    * In upsert mode, a dynamic table and an external connector exchange UPSERT and DELETE messages.
    *
    * This mode requires a (possibly composite) unique key by which updates can be propagated. The
    * external connector needs to be aware of the unique key attribute in order to apply messages
    * correctly. INSERT and UPDATE changes are encoded as UPSERT messages. DELETE changes as
    * DELETE messages.
    *
    * The main difference to a retract stream is that UPDATE changes are encoded with a single
    * message and are therefore more efficient.
    *
    * @see See also [[inAppendMode()]] and [[inRetractMode()]].
    */
  def inUpsertMode(): D
}