Custom EventHubDataAdapter for EventHub Messages Without Partition Key

[klasrpersson]

I'm trying to build a custom EventHubDataAdapter to process EventHub messages that originate from EventGrid. These messages:

• Do not have the stream namespace set as a property
• Are sent without a partition key

I started with the CustomDataAdapter sample project and attempted to hardcode both the stream namespace and the stream key. However, this approach doesn't seem to work reliably — I only receive messages from the first partition.

All messages are read from EventHub and placed in the internal cache but then only some of them get all the way to the grain.

As a test, I modified the adapter to randomize a unique stream key for each message. With this change, all messages reach a grain as expected but obviously not the correct grain since is was just randomized.

Given this behavior i thought i could have something to do with the usage of QualifiedStreamId in the PersistentStreamPullingAgent but im not sure.

Questions:

• Is there an expectation that all messages for a given grain (i.e., stream key) must always come from the same EventHub partition?
• If so, does this mean it's not possible to support scenarios where the sender does not specify a partition key?

Any guidance or recommendations would be appreciated!