What is CQRS (Command Query Responsibility Segregation)?

CQRS (Command Query Responsibility Segregation) is a design pattern that separates read operations (queries) and write operations (commands) for data in an application.

Main principles:

1. Separation of operations: Commands change the system's state but do not return data (except possibly the ID of the created resource). Queries return data but do not change the state.
2. Different data models: Often, optimized data models are used for commands and queries. For example, a relational database might be used for writing, and a NoSQL database optimized for specific views for reading.
3. Asynchronous execution of commands: Changing the state after executing a command can occur asynchronously, especially in conjunction with Event Sourcing.

Advantages:

• Scalability: Read and write operations can be scaled independently.
• Performance: Optimization of each side (query/command) for its specific tasks.
• Flexibility: More flexible architecture for complex domains.
• Separation of concerns: Clear separation of read and write logic.

Disadvantages:

• Complexity: Implementing CQRS adds architectural complexity.
• Consistency: There may be issues with data consistency between read and write models (eventual consistency).

Application in Frontend: Although CQRS is more commonly used on the backend, understanding this pattern is useful for understanding the architecture of client-server interactions, especially in applications using Event Sourcing or requiring high read/write performance. The frontend interacts with CQRS through APIs that explicitly separate endpoints for commands (POST, PUT, DELETE) and queries (GET).