| /* |
| * 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.api.functions; |
| |
| import org.apache.flink.api.common.functions.InvalidTypesException; |
| import org.apache.flink.table.api.ValidationException; |
| import org.apache.flink.table.api.types.DataType; |
| import org.apache.flink.table.api.types.DataTypes; |
| |
| /** |
| * Base class for User-Defined Aggregates. |
| * |
| * <p>The behavior of an {@link AggregateFunction} can be defined by implementing a series of |
| * custom methods. An {@link AggregateFunction} needs at least three methods: |
| * - createAccumulator, |
| * - accumulate, and |
| * - getValue. |
| * |
| * <p>There are a few other methods that can be optional to have: |
| * - retract, |
| * - merge, and |
| * - resetAccumulator |
| * |
| * <p>All these methods muse be declared publicly, not static and named exactly as the names |
| * mentioned above. The methods createAccumulator and getValue are defined in the |
| * {@link AggregateFunction} functions, while other methods are explained below. |
| * |
| * |
| * {@code |
| * Processes the input values and update the provided accumulator instance. The method |
| * accumulate can be overloaded with different custom types and arguments. An AggregateFunction |
| * requires at least one accumulate() method. |
| * |
| * param accumulator the accumulator which contains the current aggregated results |
| * param [user defined inputs] the input value (usually obtained from a new arrived data). |
| * |
| * public void accumulate(ACC accumulator, [user defined inputs]) |
| * } |
| * |
| * |
| * {@code |
| * Retracts the input values from the accumulator instance. The current design assumes the |
| * inputs are the values that have been previously accumulated. The method retract can be |
| * overloaded with different custom types and arguments. This function must be implemented for |
| * datastream bounded over aggregate. |
| * |
| * param accumulator the accumulator which contains the current aggregated results |
| * param [user defined inputs] the input value (usually obtained from a new arrived data). |
| * |
| * public void retract(ACC accumulator, [user defined inputs]) |
| * } |
| * |
| * |
| * {@code |
| * Merges a group of accumulator instances into one accumulator instance. This function must be |
| * implemented for datastream session window grouping aggregate and dataset grouping aggregate. |
| * |
| * param accumulator the accumulator which will keep the merged aggregate results. It should |
| * be noted that the accumulator may contain the previous aggregated |
| * results. Therefore user should not replace or clean this instance in the |
| * custom merge method. |
| * param its an {@link Iterable} pointed to a group of accumulators that will be |
| * merged. |
| * |
| * public void merge(ACC accumulator, Iterable<ACC> its) |
| * } |
| * |
| * |
| * {@code |
| * Resets the accumulator for this {@link AggregateFunction}. This function must be implemented for |
| * dataset grouping aggregate. |
| * |
| * param accumulator the accumulator which needs to be reset |
| * |
| * public void resetAccumulator(ACC accumulator) |
| * } |
| * |
| * @param <T> the type of the aggregation result |
| * @param <ACC> the type of the aggregation accumulator. The accumulator is used to keep the |
| * aggregated values which are needed to compute an aggregation result. |
| * AggregateFunction represents its state using accumulator, thereby the state of the |
| * AggregateFunction must be put into the accumulator. |
| */ |
| public abstract class AggregateFunction<T, ACC> extends UserDefinedFunction { |
| |
| /** |
| * Creates and init the Accumulator for this {@link AggregateFunction}. |
| * |
| * @return the accumulator with the initial value |
| */ |
| public abstract ACC createAccumulator(); |
| |
| /** |
| * Called every time when an aggregation result should be materialized. |
| * The returned value could be either an early and incomplete result |
| * (periodically emitted as data arrive) or the final result of the |
| * aggregation. |
| * |
| * @param accumulator the accumulator which contains the current |
| * aggregated results |
| * @return the aggregation result |
| */ |
| public abstract T getValue(ACC accumulator); |
| |
| /** |
| * Returns true if this AggregateFunction can only be applied in an OVER window. |
| * |
| * @return true if the AggregateFunction requires an OVER window, false otherwise. |
| */ |
| public boolean requiresOver() { |
| return false; |
| } |
| |
| /** |
| * Returns the DataType of the AggregateFunction's result. |
| * |
| * @return The DataType of the AggregateFunction's result or null if the result type |
| * should be automatically inferred. |
| */ |
| public DataType getResultType() { |
| return null; |
| } |
| |
| /** |
| * Returns the DataType of the AggregateFunction's accumulator. |
| * |
| * @return The DataType of the AggregateFunction's accumulator or null if the |
| * accumulator type should be automatically inferred. |
| */ |
| public DataType getAccumulatorType() { |
| return null; |
| } |
| |
| public DataType[] getUserDefinedInputTypes(Class[] signature) { |
| DataType[] types = new DataType[signature.length]; |
| try { |
| for (int i = 0; i < signature.length; i++) { |
| types[i] = DataTypes.extractDataType(signature[i]); |
| } |
| } catch (InvalidTypesException e) { |
| throw new ValidationException("Parameter types of scalar function '" + |
| getClass().getCanonicalName() + "' cannot be automatically determined. " + |
| "Please provide data type manually."); |
| } |
| return types; |
| } |
| |
| } |