org.apache.flink.table.functions.DeclarativeAggregateFunction Maven / Gradle / Ivy
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/*
* 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
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* 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.functions;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.table.catalog.DataTypeFactory;
import org.apache.flink.table.expressions.Expression;
import org.apache.flink.table.expressions.UnresolvedReferenceExpression;
import org.apache.flink.table.types.DataType;
import org.apache.flink.table.types.inference.TypeInference;
import org.apache.flink.util.Preconditions;
import java.util.Arrays;
import java.util.Set;
import java.util.stream.Collectors;
import static org.apache.flink.table.expressions.ApiExpressionUtils.unresolvedRef;
/**
* API for aggregation functions that are expressed in terms of expressions.
*
* When implementing a new expression-based aggregate function, you should first decide how many
* operands your function will have by implementing {@link #operandCount} method. And then you can
* use {@link #operand} fields to represent your operand, like `operand(0)`, `operand(2)`.
*
*
Then you should declare all your buffer attributes by implementing {@link
* #aggBufferAttributes}. You should declare all buffer attributes as {@link
* UnresolvedReferenceExpression}, and make sure the name of your attributes are unique within the
* function and it should not conflict with operandIndex. You can then use these attributes when
* defining {@link #initialValuesExpressions}, {@link #accumulateExpressions}, {@link
* #mergeExpressions} and {@link #getValueExpression}.
*
*
Note: Developer of DeclarativeAggregateFunction should guarantee that the inferred type of
* {@link #getValueExpression} is the same as {@link #getResultType()}
*
*
See an full example: {@code AvgAggFunction}.
*/
@PublicEvolving
public abstract class DeclarativeAggregateFunction extends UserDefinedFunction {
private transient Set aggBufferNamesCache;
/** How many operands your function will deal with. */
public abstract int operandCount();
/** All fields of the aggregate buffer. */
public abstract UnresolvedReferenceExpression[] aggBufferAttributes();
/** All types of the aggregate buffer. */
public abstract DataType[] getAggBufferTypes();
/** The result type of the function. */
public abstract DataType getResultType();
/** Expressions for initializing empty aggregation buffers. */
public abstract Expression[] initialValuesExpressions();
/** Expressions for accumulating the mutable aggregation buffer based on an input row. */
public abstract Expression[] accumulateExpressions();
/** Expressions for retracting the mutable aggregation buffer based on an input row. */
public abstract Expression[] retractExpressions();
/**
* A sequence of expressions for merging two aggregation buffers together. When defining these
* expressions, you can use the syntax {@code attributeName} and {@code
* mergeOperand(attributeName)} to refer to the attributes corresponding to each of the buffers
* being merged.
*/
public abstract Expression[] mergeExpressions();
/** An expression which returns the final value for this aggregate function. */
public abstract Expression getValueExpression();
private Set getAggBufferNames() {
if (aggBufferNamesCache == null) {
aggBufferNamesCache =
Arrays.stream(aggBufferAttributes())
.map(UnresolvedReferenceExpression::getName)
.collect(Collectors.toSet());
}
return aggBufferNamesCache;
}
private void validateOperandName(String name) {
if (getAggBufferNames().contains(name)) {
throw new IllegalStateException(
String.format("Agg buffer name(%s) should not same to operands.", name));
}
}
/**
* Args of accumulate and retract, the input value (usually obtained from a new arrived data).
*/
public final UnresolvedReferenceExpression[] operands() {
int operandCount = operandCount();
Preconditions.checkState(
operandCount >= 0, "inputCount must be greater than or equal to 0.");
UnresolvedReferenceExpression[] ret = new UnresolvedReferenceExpression[operandCount];
for (int i = 0; i < operandCount; i++) {
String name = String.valueOf(i);
validateOperandName(name);
ret[i] = unresolvedRef(name);
}
return ret;
}
/**
* Arg of accumulate and retract, the input value (usually obtained from a new arrived data).
*/
public final UnresolvedReferenceExpression operand(int i) {
String name = String.valueOf(i);
if (getAggBufferNames().contains(name)) {
throw new IllegalStateException(
String.format("Agg buffer name(%s) should not same to operands.", name));
}
return unresolvedRef(name);
}
/**
* Merge input of {@link #mergeExpressions()}, the input are AGG buffer generated by user
* definition.
*/
public final UnresolvedReferenceExpression mergeOperand(
UnresolvedReferenceExpression aggBuffer) {
String name = String.valueOf(Arrays.asList(aggBufferAttributes()).indexOf(aggBuffer));
validateOperandName(name);
return unresolvedRef(name);
}
/**
* Merge inputs of {@link #mergeExpressions()}, these inputs are agg buffer generated by user
* definition.
*/
public final UnresolvedReferenceExpression[] mergeOperands() {
UnresolvedReferenceExpression[] aggBuffers = aggBufferAttributes();
UnresolvedReferenceExpression[] ret = new UnresolvedReferenceExpression[aggBuffers.length];
for (int i = 0; i < aggBuffers.length; i++) {
String name = String.valueOf(i);
validateOperandName(name);
ret[i] = unresolvedRef(name);
}
return ret;
}
@Override
public FunctionKind getKind() {
return FunctionKind.OTHER;
}
@Override
public TypeInference getTypeInference(DataTypeFactory factory) {
throw new UnsupportedOperationException();
}
}