Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/3829#discussion_r136850229
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/api/BatchTableEnvironment.scala
---
@@ -106,6 +106,43 @@ abstract class BatchTableEnvironment(
}
/**
+ * Registers an external [[TableSink]] in this [[TableEnvironment]]'s
catalog.
+ * Registered sink tables can be referenced in SQL DML clause.
+ *
+ * Examples:
+ *
+ * - predefine a table sink with schema
--- End diff --
I proposed this API for the following reason:
I would like to have a common API and preconditions for pre-registered and
on-demand used table sinks such that all (also existing) table sinks can be
used in both of these use cases.
There is already the `configure()` method which has exactly the purpose of
setting the field names and types. Currently, this method is only internally
called during the translation process. Of course, users could implement a
`TableSink` by setting field names and types in the constructor (as shown in
the Scala docs of this PR), but I think this would kind of circumvent the
current API and might lead to `TableSink` implementations that can be either
used in a pre-registered or an on-demand setting. Hence, I think it would be
better to "enforce" the use of the `configure()` method by designing the API
such that the `configure()` method is always internally called and hence
mandatory. That way we can guarantee that each `TableSink` can be used in both
cases because both use case require `configure()` and use it in the same way.
We could ask users to call the `configure()` method before registering the
table sink with an error message (as @wuchong proposed) or enforce this through
the API. I think the second approach is better because users would not
experience an exception. In my opinion, we should at least "encourage" the use
of the `configure()` method by not giving an example that sets field names and
types in the constructor.
What do you think @lincoln-lil and @wuchong ?
---
