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I have a question about event-sourcing, how can we validate if the Aggregate can be persisted? Like the example that create a User, how to validate that user has already exists? To restore all the aggregate from event is to expensive. And just check usercreatedevent is also not enough, because user maybe change the username or be deleted. hope you can shed some light on it

I'm looking to see if I can use this library in a commercial project. I'm not seeing a license file, are you already releasing it with a license? If not, would you be open to add one?

I get the following error when i try to use the example provided in this git to save into dynamodb

The provided key element does not match the schema [ValidationException]: ValidationException: The provided key element does not match the schema

how can i solve this problem please.

Culprit:

loadVersion can fail for reasons other than "not found", such as "store implementation has connectivity outage" etc. You do not want to discard such errs and fall back on a newly-instantiated empty aggregate here...

A fix to this would do so only for errs of type eventsource.Error with a Code() of eventsource.ErrAggregateNotFound I reckon? --- with all other errs being properly returned immediately.

@savaki Hey I hope here is an appropriate place to ask --

Do you have any recommendations or tools in place for cleaning up after prototyping? E.g. removing the S3 archive and DynamoDB tables after testing an application and before switching to "production"?

Also is there anything in place for versioning of the eventstream (e.g. if a schema changes -- or if we want to switch from a staging > production queue)

Thanks! I loved your gopherfest talk and missed out during the q/a.

@savaki this is more just a question of how you deal with streams using a AWS pipeline. Watching your talk the overall structure makes sense but details are a little fuzzy for someone not engrossed in the AWS stack.

With event stores I've used before you'd have a features such as indexing like in EventStore which can allow for viewing of all events across the system, per aggregate type, or via your own projections using linkTo(streamId, event, metadata).

I know event sourcing and CQRS are orthogonal but how do you deal with the query/projection side after events are written out to Dynamo?

This is mostly a question whether it is in scope and/or if you have thought about this use case.

The API supports loading an aggregate at a particular version of itself, but If I wanted to get the state of two aggregates at some point in time, my understanding is that there is no way of doing this since the version is local to the aggregate. Since Repository.Save takes multiple events which may span multiple aggregates, they are being transactionally saved together (at least conceptually) and thus could/should represent an atomic change in state in the repo.

If there was a repo-level transaction id generated (monotonically increasing) on each call and added to each record, then an aggregate can be loaded relative to the transaction id which means the state of all aggregates in the repo could be loaded with respect to some point in time. At that point you could get a copy of the repo "as of" some transaction (or time).

// Initialize.
r := eventsource.New(...)

// Perform 10 calls to r.Save() so tx = 10 by the end

// Get the repo as-of transaction 5.
r5 := r.Asof(5)

bobAt5 := r5.Load(ctx, "bob")
bob := r.Load(ctx, "bob")

A timestamp could be associated with each transaction id so Asof could be a real time.Time rather than the transaction id or AsofT for txid and Asof for time.

Watch the talk and tried to run the gopherfest example, unfortunately got the error file: 'github.com/altairsix/eventsource/_examples/gopherfest/main.go' severity: 'Error' message: 'undefined: eventsource.NewDispatcher' at: '98,2' source: ''

Has the examples been checked for the against the latest revisions?

Comparing between protocol buffer events leads to uncomparrable error with []uint8 arrays.