Github user aljoscha commented on the pull request:
https://github.com/apache/flink/pull/2051#issuecomment-222648249
Hi,
just some high-level remarks about the API of `KeyedStream` and
`QueryableStateStream`. You could parameterize them both by the State type.
This way you would also get a very nice way of generically accessing the
different types of state on the query side. Let me quickly show what I mean.
`KeyedStream` would have this method:
```
<S extends State> QueryableStateStream<KEY, S> asQueryableState(
String queryableStateName,
StateDescriptor<S, ?> stateDescriptor);
```
the signature of `QueryableStateStream` would be like this:
```
public class QueryableStateStream<K, S extends State> {
private StateDescriptor<S, ?> stateDescriptor;
/**
* Read the state represented by this stream using a state client
*/
public S read(K key, QueryableStateClient client) {
return stateDescriptor.bind(new QueryStateBinder(client.read(key,
stateName)));
}
}
```
The nice thing about `StateDescriptor.bind()` is that you can use this to
create a state reader based on the state type. You pass in a custom
`StateBackend` (this should really be called `StateBinder`, btw). That
constructs a state reader that deserializes the bytes read from the state
client.
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