What is CQRS and how can it be implemented?

CQRS (Command Query Responsibility Segregation) is an architectural pattern that separates read (Query) and write (Command) operations on data into different models. The idea is that commands change the system's state, while queries only read data, allowing each part to be optimized separately.

Implementing CQRS typically involves:

• Separate interfaces and models for commands and queries.
• Commands are processed through handlers that change the state (e.g., update the database).
• Queries are handled through separate handlers that return data, possibly from read-optimized stores.

Example in Go (simplified):

// Command
func UpdateUserName(userID string, newName string) error {
    // update the user's name in the database
    return nil
}

// Query
func GetUserName(userID string) (string, error) {
    // retrieve the user's name from the database
    return "Alice", nil
}

In more complex systems, CQRS can be accompanied by Event Sourcing, where state changes are recorded as events.