flink-libraries/flink-table/src/main/java/org/apache/flink/table/api/functions/CustomTypeDefinedFunction.java

/*
 * 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;

/**
 * {@link UserDefinedFunction} to define its parameterTypes.
 */
public abstract class CustomTypeDefinedFunction extends UserDefinedFunction {

	/**
	 * Returns {@link DataType} about the operands of the evaluation method with a given
	 * signature.
	 *
	 * <p>In order to perform operand type inference in SQL (especially when NULL is used) it might
	 * be necessary to determine the parameter {@link DataType} of an evaluation method.
	 * By default Flink's type extraction facilities are used for this but might be wrong for
	 * more complex, custom, or composite types.
	 *
	 * @param signature signature of the method the operand types need to be determined
	 * @return {@link DataType} of  operand types
	 */
	public DataType[] getParameterTypes(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;
	}

	/**
	 * Returns the result type of the evaluation method with a given signature.
	 *
	 * <p>This method needs to be overriden in case Flink's type extraction facilities are not
	 * sufficient to extract the [[DataType]] based on the return type of the evaluation
	 * method. Flink's type extraction facilities can handle basic types or
	 * simple POJOs but might be wrong for more complex, custom, or composite types.
	 *
	 * <p>The input arguments are the input arguments which are passed to the eval() method.
	 * Only the literal arguments (constant values) are passed to the [[getResultType()]] method.
	 * If non-literal arguments appear, it will pass nulls instead.
	 *
	 * <p>The argument types are also passed to the method. These argument types would allow to
	 * determine the return type based on the used eval() method.
	 *
	 * @param arguments arguments of a function call (only literal arguments
	 *                  are passed, nulls for non-literal ones)
	 * @param argTypes The classes of the arguments of the called eval() method.
	 * @return [[DataType]] of result type or null if Flink should determine the type
	 */
	public DataType getResultType(Object[] arguments, Class[] argTypes) {
		return null;
	}
}