flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/TemporalTableFunction.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,
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 * See the License for the specific language governing permissions and
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 */

package org.apache.flink.table.functions

import java.sql.Timestamp

import org.apache.flink.api.java.typeutils.RowTypeInfo
import org.apache.flink.table.api.Table
import org.apache.flink.table.expressions.Expression
import org.apache.flink.types.Row

/**
  * Class representing temporal table function over some history table.
  * It takes one single argument, the `timeAttribute`, for which it returns matching version of
  * the `underlyingHistoryTable`, from which this [[TemporalTableFunction]] was created.
  *
  * This function shouldn't be evaluated. Instead calls to it should be rewritten by the optimiser
  * into other operators (like Temporal Table Join).
  */
class TemporalTableFunction private(
    @transient private val underlyingHistoryTable: Table,
    private val timeAttribute: Expression,
    private val primaryKey: String,
    private val resultType: RowTypeInfo)
  extends TableFunction[Row] {

  def eval(row: Timestamp): Unit = {
    throw new IllegalStateException("This should never be called")
  }

  override def getResultType: RowTypeInfo = {
    resultType
  }

  def getTimeAttribute: Expression = {
    timeAttribute
  }

  def getPrimaryKey: String = {
    primaryKey
  }

  private[flink] def getUnderlyingHistoryTable: Table = {
    if (underlyingHistoryTable == null) {
      throw new IllegalStateException("Accessing table field after planing/serialization")
    }
    underlyingHistoryTable
  }
}

object TemporalTableFunction {
  private[flink] def create(
      table: Table,
      timeAttribute: Expression,
      primaryKey: String): TemporalTableFunction = {
    new TemporalTableFunction(
      table,
      timeAttribute,
      primaryKey,
      new RowTypeInfo(
        table.getSchema.getFieldTypes,
        table.getSchema.getFieldNames))
  }
}