March 2025
Intermediate to advanced
202 pages
4h 45m
English
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Working with Event Sourcing Aggregates
In this chapter, you’ve actually been building what Martin Fowler[7] calls an aggregate without labeling it as such. At a conceptual level, an aggregate is a single, uniquely identifiable entity that has state, validates commands, and emits events.
Every aggregate must have a unique identifier or key. This differentiates one aggregate from another within the same event stream. By way of example, consider a group or a class called BankAccount. Given a stream of ledger events, the key that differentiates one aggregate from another might be the key field account_number. In this case, you can say that there’s an aggregate type called BankAccount, and one aggregate (or aggregate instance, depending on where ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.