Event sourcing example in Java

A simplified (in memory) example of Event Sourcing implementation in Java for banking domain. Repository is splitted into exercises adding step by step more functionality towards good design of event sourcing with CQRS. You can play around and try to implement exercises or You can check out solution branches.

Step 1 - In memory iplementation of event sourcing

• Provide simple in-memory implementation of Event Store
• Make all test passing using event sourcing

soultion

• branch exercise_1_solution

Step 1a (optional) - Unit of work pattern

• Implement Unit of Work pattern where events are stored outside of aggregate

soultion

• WIP

Step 1b (optional) - Projections

• Implement Projections on Account to get number of transactions performed on account
• eventStore.store() method shoud accept Event playload instead of domain Events
• what should be api of eventStream()?

soultion

• WIP

Step 2 (optional) - Optimistic locking

• add optimistic locking

soultion

• WIP

Step 3 - new Aggregate extraction

• Refactor to move all money transfer related stuff to separate aggregate
• New aggregate will be also using Event Store

soultion

• WIP

Step 4 - adding CQRS

• Apply CQRS rule and separate the command and reading side
• Solution will use Eventual Consistency approach

soultion

• WIP

Step 5

• Provide additional (not transient) implementation of Event Store. (https://geteventstore.com/)

soultion

• WIP