Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/2562#discussion_r82971688
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/runtime/aggregate/PropertyRead.scala
---
@@ -0,0 +1,33 @@
+/*
+ * 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.runtime.aggregate
+
+import org.apache.flink.streaming.api.windowing.windows.Window
+
+/**
+ * Base class for reading a window property. The property will be
extracted once and
+ * can be read multiple times.
+ */
+trait PropertyRead[T] extends Serializable {
+
+ def extract(window: Window): Unit
--- End diff --
I think we do not need a generic interface to extract properties. The
`extract` method requires a window object but not all properties might be
present in the window object. So I am not sure how much generalization is
required here.
I think we can implement a `TimeWindowPropertyCollector` that works as
follows:
```
class TimeWindowPropertyCollector(start: Int, end: Int) extends
Collector[Row] {
var finalCollector: Collector[Row] = _
var timeWindow: TimeWindow = _
override def collect(record: Row): Unit = {
if (start > -1) {
record.setField(start, timeWindow.getStart)
}
if (end > -1) {
record.setField(end, timeWindow.getEnd)
}
finalCollector.collect(record)
}
override def close(): Unit = finalCollector.close()
}
```
If we (ever) need more properties, we can add another wrapping collector or
change the design. But at this point I think this is sufficient.
What do you think?
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