Description

Event Sourcing stores the state of a business entity as a sequence of state-changing events. Whenever the state of a business entity changes, a new event is appended to the list of events. The current state is reconstructed by replaying the events.

Where to use

• Audit logging and compliance.
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• Financial ledgers and accounting systems.
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• Complex domains where history is important (DDD).

Real World Example

A Bank Account. Instead of storing 'Balance: 100', we store [Deposited 50, Withdrew 10, Deposited 60]. The balance is calculated on the fly.

Code Example

# Code Concept for Event Sourcing
# This pattern is architectural.

class Service:
    def execute(self):
        # Implementation logic
        pass