using with easy source 2.0.3

[yonahforst]

I just ran into a problem when trying to use this with the latest easy source (2.0.3).

easy source projections expects the eventSource.scan() function to accept a version number (essentially an offset) but dynamodb doesn't allow query offsets. The only keys in this library suitable are commitId and commitedAt and those aren't included in the 'EventStream

[yonahforst]

@bakerface - Here's how I'm breaking down this problem:

Given that:

• Projections need to keep track of which events were already processed per event source, and query for new ones.
• DynamoDb cannot be queried using offsets.

Then:

• Projections need to use something from the event when scanning for new ones
• Event sources need to index events by that something key
• Either the event sources dictate which key to use or the projections dictate it

I think it makes the most sense to use the at key from each event. For this library, we would have to add a new key called 'lastEventAt' and use that key in GSI and scan function.

What do you think?

[yonahforst]

ok, I'm thinking more about this. Originally the scan function was supposed to use the commitId which is the datetime+aggregateId. I was the one who changed it to use the version number instead, that was a mistake.

The problem with using the commitId is that aggregateIds are not a fixed length. So a shorter aggregateId with a later datetime would sort before a longer aggregateId with an earlier datetime.

i can think of three ways to solve this. 1) Either enforce a fixed length for aggregateIds, 2) pad / trim them when using for the commitId, or 3) use only the datetime, and not the aggregateId