Hi Steven,
We do still have this on the roadmap, and intend on adding the feature to start a projection from now shortly after the next major release.
The linked github issues are here and here if anyone would like to track their progress.
We will also be releasing filtered reads soon, which may help in situations like this. You would be able to specify the category as a stream prefix and read from a specific position in the $all stream.
As a workaround for right now, you could write your own checkpoint for the projection.
To do this you would need to do something like :
- Stop the projection
- Copy an existing checkpoint from the
$projections-{projection_name}-checkpointstream - Update the position or version number in the checkpoint event
- Write it back to the checkpoint stream, ensuring you keep the same metadata as the existing checkpoint event
- Start the projection again