Understanding CQRS: Command Query Responsibility Segregation

Here’s a diagram that explains the CQRS (Command Query Responsibility Segregation) pattern. I’ll first describe it in detail and then provide the image: Diagram Description Client: The user interface or API that sends commands and queries. Command: Represents an action that changes the state of the system (e.g., CreateOrder, UpdateCustomer). Query: Represents a request for data without changing the state (e.g., GetOrder, GetCustomerDetails). Command Handler: Processes the command and updates the data in the Write Model. Write Model (Data Store): The data store where the state-changing operations are performed. Event: Represents the outcome of a command and is used to update other parts of the system. Event Store: Stores the events generated by command handlers. Event Handler: Listens to events and updates the Read Model. Read Model (Data Store): Optimized for read operations, often denormalized for fast querying. Query Handler: Retrieves data from the Read Model in response to queries. The separation of write and read models allows for independent optimization, scalability, and security for both operations. ...

March 15, 2025 · 2 min · Taner