leonardBang commented on a change in pull request #9545: [FLINK-13355][docs]
Add documentation for Temporal Table Join in blink planner
URL: https://github.com/apache/flink/pull/9545#discussion_r318947040
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File path: docs/dev/table/sourceSinks.zh.md
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@@ -324,6 +324,46 @@ FilterableTableSource[T] {
{% top %}
+### Defining a TableSource with Lookupable
+
+The `LookupableTableSource` interface adds support for the table to be
accessed via key column(s) in a lookup fashion. This is very useful when used
to join with a dimension table to enrich some information. If you want to use
the `TableSource` in lookup mode, you should use the source in [temporal table
join syntax](streaming/joins.html).
+
+The interface looks as follows:
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+LookupableTableSource<T> implements TableSource<T> {
+
+ public TableFunction<T> getLookupFunction(String[] lookupkeys);
+
+ public AsyncTableFunction<T> getAsyncLookupFunction(String[] lookupkeys);
+
+ public boolean isAsyncEnabled();
+}
+{% endhighlight %}
+</div>
+
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+LookupableTableSource[T] extends TableSource[T] {
+
+ def getLookupFunction(lookupKeys: Array[String]): TableFunction[T]
+
+ def getAsyncLookupFunction(lookupKeys: Array[String]): AsyncTableFunction[T]
+
+ def isAsyncEnabled: Boolean
+}
+{% endhighlight %}
+</div>
+</div>
+
+* `getLookupFunction(lookupkeys)`: Returns a `TableFunction` which used to
lookup the matched row(s) via lookup keys. The lookupkeys are the field names
of `LookupableTableSource` in the join equal conditions. The eval method
parameters of the returned `TableFunction`'s should be in the order which
`lookupkeys` defined. It is recommended to define the parameters in varargs
(e.g. `eval(Object... lookupkeys)` to match all the cases). The return type of
the `TableFunction` must be identical to the return type defined by the
`TableSource.getReturnType()` method.
+* `getAsyncLookupFunction(lookupkeys)`: Optional. Similar to
`getLookupFunction`, but the `AsyncLookupFunction` lookups the matched row(s)
asynchronously. The underlying of `AsyncLookupFunction` will be called via
[Async I/O](/dev/stream/operators/asyncio.html). The first argument of the eval
method of the returned `AsyncTableFunction` should be defined as
`java.util.concurrent.CompletableFuture` to collect results asynchronously
(e.g. `eval(CompletableFuture<Collection<String>> result, Object...
lookupkeys)`). Can throw an exception if the TableSource doesn't support
asynchronously lookup.
Review comment:
the same as above
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