Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/2653#discussion_r88336271
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/functions/TableFunction.scala
---
@@ -0,0 +1,119 @@
+/*
+ * 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.api.table.functions
+
+import org.apache.calcite.sql.SqlFunction
+import org.apache.flink.annotation.Internal
+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.api.table.{ValidationException, FlinkTypeFactory}
+
+import scala.collection.mutable.ListBuffer
+
+/**
+ * Base class for a user-defined table function (UDTF). A user-defined
table functions works on
+ * one row as input and returns multiple rows as output.
+ *
+ * The behavior of a [[TableFunction]] can be defined by implementing a
custom evaluation
+ * method. An evaluation method must be declared publicly and named
"eval". Evaluation methods
+ * can also be overloaded by implementing multiple methods named "eval".
+ *
+ * User-defined functions must have a default constructor and must be
instantiable during runtime.
+ *
+ * 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
[[TypeInformation]] of the result type
+ * can be manually defined by overriding [[getResultType()]].
+ *
+ * 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. DATE/TIME is equal to int, TIMESTAMP is equal to long.
+ *
+ * @tparam T The type of the output row
+ */
+abstract class TableFunction[T] extends UserDefinedFunction with
EvaluableFunction {
+
+ private val rows: ListBuffer[T] = new ListBuffer
+
+ /**
+ * Emit an output row
+ *
+ * @param row the output row
+ */
+ protected def collect(row: T): Unit = {
+ // cache rows for now, maybe immediately process them further
+ rows += row
+ }
+
+
+ @Internal
+ def getRowsIterator = rows.toIterator
+
+ @Internal
+ def clear() = rows.clear()
+
+ // this method will not be called, because we need to register multiple
sql function at one time
+ override private[flink] final def createSqlFunction(
+ name: String,
+ typeFactory: FlinkTypeFactory)
+ : SqlFunction = {
+ throw new UnsupportedOperationException("this method should not be
called")
+ }
+
+ //
----------------------------------------------------------------------------------------------
+
+ /**
+ * Returns the result type of the evaluation method with a given
signature.
+ *
+ * This method needs to be overriden in case Flink's type extraction
facilities are not
+ * sufficient to extract the [[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 [[TypeInformation]] of result type or null if Flink should
determine the type
+ */
+ def getResultType: TypeInformation[T] = null
+
+ /**
+ * Returns [[TypeInformation]] about the operands of the evaluation
method with a given
+ * signature.
+ *
+ * In order to perform operand type inference in SQL (especially when
NULL is used) it might be
+ * necessary to determine the parameter [[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 [[TypeInformation]] of operand types
+ */
+ def getParameterTypes(signature: Array[Class[_]]):
Array[TypeInformation[_]] = {
+ signature.map { c =>
+ try {
+ TypeExtractor.getForClass(c)
+ } catch {
+ case ite: InvalidTypesException =>
+ throw new ValidationException(
+ s"Parameter types of scalar function '$this' cannot be " +
--- End diff --
`scalar function` -> `table function`.
Can you also extend the exception with instructions how to provide type
information manually (I guess by overriding `getParameterTypes`, right?)
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