CQRS Explained: Separate Read and Write Models Without Overengineering

CQRS Explained: Separate Read and Write Models Without Overengineering

Command Query Responsibility Segregation (CQRS) separates the model used to change state from the model used to read state.

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CQRS Does Not Require Two Databases

A simple CQRS design can use one database with separate command and query code paths.

This is often enough when writes need rich domain validation while reads need optimized projections or DTOs.

Separate Stores Are an Advanced Option

At larger scale:

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Separate stores allow independent read/write scaling and query-optimized schemas, but they introduce eventual consistency and projection/recovery complexity.

CQRS vs Event Sourcing

They are related but independent patterns.

• CQRS separates reads from writes.
• Event sourcing stores state changes as an append-only event history.

You can use CQRS without event sourcing. Combining both is useful only when the domain actually benefits from event history and projections.

When CQRS Helps

Good candidates include systems where:

• read and write workloads differ significantly
• reads need denormalized/materialized views
• write-side business rules are complex
• read and write sides need independent scaling

For ordinary CRUD screens, separate models, stores, and projection pipelines can add more complexity than value.

Final Takeaway

CQRS is fundamentally about separating read and write responsibilities, not automatically introducing events, brokers, and multiple databases. Start with separate models/interfaces; add independently stored read projections only when workload or domain complexity justifies them.

References

• Azure Architecture Center: CQRS Pattern
• Azure Architecture Center: Event Sourcing Pattern