| /* |
| * 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.functions; |
| |
| import org.apache.flink.annotation.PublicEvolving; |
| import org.apache.flink.api.common.functions.InvalidTypesException; |
| import org.apache.flink.api.common.typeinfo.TypeInformation; |
| import org.apache.flink.api.java.typeutils.TypeExtractor; |
| import org.apache.flink.table.api.ValidationException; |
| import org.apache.flink.util.Collector; |
| |
| /** |
| * Base class for a user-defined table function (UDTF). A user-defined table functions works on |
| * zero, one, or multiple scalar values as input and returns multiple rows as output. |
| * |
| * <p>The behavior of a {@link TableFunction} can be defined by implementing a custom evaluation |
| * method. An evaluation method must be declared publicly, not static, and named <code>eval</code>. |
| * Evaluation methods can also be overloaded by implementing multiple methods named <code>eval</code>. |
| * |
| * <p>User-defined functions must have a default constructor and must be instantiable during runtime. |
| * |
| * <p>By default the result type of an evaluation method is determined by Flink's type extraction |
| * facilities. This is sufficient for basic types or simple POJOs but might be wrong for more |
| * complex, custom, or composite types. In these cases {@link TypeInformation} of the result type |
| * can be manually defined by overriding {@link TableFunction#getResultType}. |
| * |
| * <p>Internally, the Table/SQL API code generation works with primitive values as much as possible. |
| * If a user-defined table function should not introduce much overhead during runtime, it is |
| * recommended to declare parameters and result types as primitive types instead of their boxed |
| * classes. <code>DATE/TIME</code> is equal to <code>int</code>, <code>TIMESTAMP</code> is equal |
| * to <code>long</code>. |
| * |
| * <p>For Example: |
| * |
| * <pre> |
| * {@code |
| * public class Split extends TableFunction<String> { |
| * |
| * // implement an "eval" method with as many parameters as you want |
| * public void eval(String str) { |
| * for (String s : str.split(" ")) { |
| * collect(s); // use collect(...) to emit an output row |
| * } |
| * } |
| * |
| * // you can overload the eval method here ... |
| * } |
| * |
| * TableEnvironment tEnv = ... |
| * Table table = ... // schema: ROW(a VARCHAR) |
| * |
| * // for Scala users |
| * val split = new Split() |
| * table.join(split('c) as ('s)).select('a, 's) |
| * |
| * // for Java users |
| * tEnv.registerFunction("split", new Split()); // register table function first |
| * table.join(new Table(tEnv, "split(a) as (s)")).select("a, s"); |
| * |
| * // for SQL users |
| * tEnv.registerFunction("split", new Split()); // register table function first |
| * tEnv.sqlQuery("SELECT a, s FROM MyTable, LATERAL TABLE(split(a)) as T(s)"); |
| * } |
| * </pre> |
| * |
| * @param <T> The type of the output row |
| */ |
| @PublicEvolving |
| public abstract class TableFunction<T> extends UserDefinedFunction { |
| |
| /** |
| * The code generated collector used to emit rows. |
| */ |
| protected Collector<T> collector; |
| |
| /** |
| * Internal use. Sets the current collector. |
| */ |
| public final void setCollector(Collector<T> collector) { |
| this.collector = collector; |
| } |
| |
| /** |
| * Returns the result type of the evaluation method with a given signature. |
| * |
| * <p>This method needs to be overridden in case Flink's type extraction facilities are not |
| * sufficient to extract the {@link TypeInformation} 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. |
| * |
| * @return {@link TypeInformation} of result type or <code>null</code> if Flink should determine the type |
| */ |
| public TypeInformation<T> getResultType() { |
| return null; |
| } |
| |
| /** |
| * Returns {@link TypeInformation} 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 TypeInformation} 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 TypeInformation} of operand types |
| */ |
| public TypeInformation<?>[] getParameterTypes(Class<?>[] signature) { |
| final TypeInformation<?>[] types = new TypeInformation<?>[signature.length]; |
| for (int i = 0; i < signature.length; i++) { |
| try { |
| types[i] = TypeExtractor.getForClass(signature[i]); |
| } catch (InvalidTypesException e) { |
| throw new ValidationException( |
| "Parameter types of table function " + this.getClass().getCanonicalName() + |
| " cannot be automatically determined. Please provide type information manually."); |
| } |
| } |
| return types; |
| } |
| |
| /** |
| * Emits an output row. |
| * |
| * @param row the output row |
| */ |
| protected final void collect(T row) { |
| collector.collect(row); |
| } |
| } |