[
https://issues.apache.org/jira/browse/FLINK-7206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16144443#comment-16144443
]
ASF GitHub Bot commented on FLINK-7206:
---------------------------------------
Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/4355#discussion_r135550350
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/api/dataview/ListView.scala
---
@@ -0,0 +1,133 @@
+/*
+ * 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.dataview
+
+import java.lang.{Iterable => JIterable}
+import java.util
+
+import org.apache.flink.api.common.typeinfo.{TypeInfo, TypeInformation}
+import org.apache.flink.table.dataview.ListViewTypeInfoFactory
+
+/**
+ * ListView provides List functionality for accumulators used by
user-defined aggregate functions
+ * {{AggregateFunction}}.
+ *
+ * A ListView can be backed by a Java ArrayList or a state backend,
depending on the context in
+ * which the function is used.
+ *
+ * At runtime `ListView` will be replaced by a
[[org.apache.flink.table.dataview.StateListView]]
+ * if it is backed by a state backend.
+ *
+ * Example:
+ * {{{
+ *
+ * public class MyAccum {
+ * public ListView<String> list;
+ * public long count;
+ * }
+ *
+ * public class MyAgg extends AggregateFunction<Long, MyAccum> {
+ *
+ * @Override
+ * public MyAccum createAccumulator() {
+ * MyAccum accum = new MyAccum();
+ * accum.list = new ListView<>(Types.STRING);
+ * accum.count = 0L;
+ * return accum;
+ * }
+ *
+ * public void accumulate(MyAccum accumulator, String id) {
+ * accumulator.list.add(id);
+ * ... ...
+ * accumulator.get()
+ * ... ...
+ * }
+ *
+ * @Override
+ * public Long getValue(MyAccum accumulator) {
+ * accumulator.list.add(id);
+ * ... ...
+ * accumulator.get()
+ * ... ...
+ * return accumulator.count;
+ * }
+ * }
+ *
+ * }}}
+ *
+ * @param elementTypeInfo element type information
+ * @tparam T element type
+ */
+@TypeInfo(classOf[ListViewTypeInfoFactory[_]])
+class ListView[T](
+ @transient private[flink] val elementTypeInfo: TypeInformation[T])
+ extends DataView {
+
+ def this() = this(null)
+
+ private[flink] var list: util.List[T] = new util.ArrayList[T]()
--- End diff --
right now an empty `ArrayList` is always created when a `ListView` is
instantiated.
This is unnecessary overhead when the `ListView` is copied or deserialized
using `ListViewSerializer` because the empty instance is immediately replaced.
We should add an option to create a `ListView` without an `ArrayList`
instance. This means we have to move the creation of the `ArrayList` out of the
primary constructor.
The same applies to the `MapView`.
> Implementation of DataView to support state access for UDAGG
> ------------------------------------------------------------
>
> Key: FLINK-7206
> URL: https://issues.apache.org/jira/browse/FLINK-7206
> Project: Flink
> Issue Type: Sub-task
> Components: Table API & SQL
> Reporter: Kaibo Zhou
> Assignee: Kaibo Zhou
>
> Implementation of MapView and ListView to support state access for UDAGG.
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
