What is the difference between event sourcing and command query separation?

What is the difference between event sourcing and command query separation?

Event sourcing is a pattern where state changes are stored as a sequence of events, while command query separation (CQS) is a principle that separates read and write operations.

Can you give me an example of how event sourcing works?

Sure! In event sourcing, instead of storing just the current state of an object, you store all the events that led to that state. For instance, if a bank account has deposits and withdrawals, each transaction is recorded as an event.

How does CQS improve application design?

CQS improves application design by making it clearer and more maintainable. By separating commands (which change state) from queries (which retrieve state), you can optimize each operation independently.

Are there any downsides to using event sourcing?

Yes, event sourcing can introduce complexity in managing event schemas and replaying events. It also requires careful consideration of how to handle event versioning.