32. What is CQRS architecture?

CQRS (Command Query Responsibility Segregation) is an architectural pattern that separates operations that modify the state of the system (commands) from operations that read data (queries). CQRS allows for the optimization of both types of operations, leading to better scalability and performance.

Advantages of CQRS:

1. Scalability: The separation of commands and queries allows for independent scaling of read and write operations, which is particularly useful in high-load systems.
2. Optimization: Different data models can be used for read and write operations, allowing for performance optimization of each.
3. Simplified business logic: CQRS simplifies business logic by separating read and write operations, allowing for independent implementation.
4. Flexibility: Easier to make changes in the system as changes in one part (e.g., writes) do not directly affect the other part (reads).

Example of implementing CQRS in Node.js:

// Commands (write)
class Command {
  constructor(type, payload) {
    this.type = type;
    this.payload = payload;
  }
}

class CommandHandler {
  handle(command) {
    switch (command.type) {
      case 'createUser':
        // create user logic
        break;
      case 'updateUser':
        // update user logic
        break;
      // other commands
    }
  }
}

// Queries (read)
class Query {
  constructor(type, criteria) {
    this.type = type;
    this.criteria = criteria;
  }
}

class QueryHandler {
  handle(query) {
    switch (query.type) {
      case 'getUserById':
        // get user by id logic
        break;
      case 'getAllUsers':
        // get all users logic
        break;
      // other queries
    }
  }
}

CQRS is a powerful architectural pattern that can significantly improve the scalability and performance of systems, particularly in high-load environments.