Software design patterns, CQRS, CQRS vs CRUD explained

A software design pattern is a reusable solution to a common problem in software design. Design patterns are not specific to any programming language or framework, but rather provide a general solution that can be implemented in different ways depending on the specific needs of a project.

Design patterns are typically classified into three categories: creational, structural, and behavioral.

  • Creational patterns: These patterns focus on the creation of objects and the management of their dependencies. Examples of creational patterns include the Singleton pattern, which ensures that only one instance of an object is created, and the Factory pattern, which enables you to create objects without specifying their concrete type.
  • Structural patterns: These patterns focus on the composition of objects and the relationships between them. Examples of structural patterns include the Adapter pattern, which enables you to adapt the interface of one object to another, and the Bridge pattern, which separates an object’s abstraction from its implementation.
  • Behavioral patterns: These patterns focus on the communication between objects and the way they collaborate to achieve a specific goal. Examples of behavioral patterns include the Observer pattern, which enables one object to observe changes in another object, and the Command pattern, which enables you to encapsulate a request as an object and pass it to a receiver.

Design patterns are useful because they provide a common vocabulary and set of best practices that can help software developers communicate more effectively and solve problems more efficiently. By using design patterns, you can leverage the collective experience of the software development community and avoid re-inventing solutions to common problems.

In summary, a software design pattern is a reusable solution to a common problem in software design. Design patterns are classified into creational, structural, and behavioral categories, and provide a common

Command Query Responsibility Segregation (CQRS)

The Command Query Responsibility Segregation (CQRS) pattern is a software design pattern that separates the responsibility of issuing commands that change the state of a system from the responsibility of querying the state of the system. In CQRS, the commands are handled by a separate set of components, known as command handlers, while the queries are handled by a separate set of components, known as query handlers.

The CQRS pattern can be used to improve the performance, scalability, and reliability of a system by allowing the command and query components to be optimized independently of each other. The command handlers can be designed to handle high volumes of requests, while the query handlers can be designed to provide fast and efficient access to the system’s data.

The CQRS pattern is often used in combination with the Event Sourcing pattern, which enables you to store the history of all changes to the system’s state as a sequence of events. This can be useful for auditing, debugging, and rolling back changes to the system.

To implement the CQRS pattern, you will need to define the commands and queries that are supported by your system, and create separate components to handle each type of request. You will also need to consider how to handle transactions and concurrency, and how to propagate changes to the system’s state to the query handlers.

In summary, the CQRS pattern is a software design pattern that separates the responsibility of issuing commands that change the state of a system from the responsibility of querying the state of the system. The CQRS pattern can be used to improve the performance, scalability, and reliability of a system, and is often used in combination with the Event Sourcing pattern.

Difference between CQRS and CRUD

Command Query Responsibility Segregation (CQRS) and Create, Read, Update, Delete (CRUD) are two different approaches to managing data in a system.

CQRS is a software design pattern that separates the responsibility of issuing commands that change the state of a system from the responsibility of querying the state of the system. In CQRS, the commands are handled by a separate set of components, known as command handlers, while the queries are handled by a separate set of components, known as query handlers. The CQRS pattern can be used to improve the performance, scalability, and reliability of a system by allowing the command and query components to be optimized independently of each other.

CRUD is a set of operations that are used to create, read, update, and delete data in a system. CRUD operations are commonly used to manage data in databases, and are implemented using create, read, update, and delete (CRUD) methods or functions. CRUD operations enable you to create new records, retrieve existing records, update existing records, and delete records from a database.

In summary, CQRS is a software design pattern that separates the responsibility of issuing commands from the responsibility of querying data, while CRUD is a set of operations that are used to manage data in a system. CQRS can be used to improve the performance, scalability, and reliability of a system, while CRUD is a commonly used approach for managing data in databases.

CQRS in C#

Here is an example of how you might implement the Command Query Responsibility Segregation (CQRS) pattern in C#:

First, you would define the commands and queries that are supported by your system. For example:

public class CreateCustomerCommand
{
    public string Name { get; set; }
    public string Email { get; set; }
}

public class UpdateCustomerCommand
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
}

public class DeleteCustomerCommand
{
    public int Id { get; set; }
}

public class GetCustomerByIdQuery
{
    public int Id { get; set; }
}

public class GetCustomersQuery
{
    public string Name { get; set; }
}


public class CreateCustomerCommandHandler : IRequestHandler<CreateCustomerCommand>
{
    private readonly ICustomerRepository _repository;

    public CreateCustomerCommandHandler(ICustomerRepository repository)
    {
        _repository = repository;
    }

    public async Task<Unit> Handle(CreateCustomerCommand request, CancellationToken cancellationToken)
    {
        var customer = new Customer
        {
            Name = request.Name,
            Email = request.Email
        };

        await _repository.AddAsync(customer);
        await _repository.SaveChangesAsync();

        return Unit.Value;
    }
}

public class UpdateCustomerCommandHandler : IRequestHandler<UpdateCustomerCommand>
{
    private readonly ICustomerRepository _repository;

    public UpdateCustomerCommandHandler(ICustomerRepository repository)
    {
        _repository = repository;
    }

    public async Task<Unit> Handle(UpdateCustomerCommand request, CancellationToken cancellationToken)
    {
        var customer = await _repository.GetByIdAsync(request.Id);
        customer.Name = request.Name;
        customer.Email = request.Email;

        await _repository.UpdateAsync(customer);
        await _repository.SaveChangesAsync();

        return Unit.Value;
    }
}

public class DeleteCustomerCommandHandler : IRequestHandler<DeleteCustomerCommand>
{
    private readonly ICustomerRepository _repository;

    public DeleteCustomerCommandHandler(ICustomerRepository repository)
    {
        _repository = repository;
    }

    public async Task<Unit> Handle(DeleteCustomerCommand request, CancellationToken cancellationToken)
    {
        var customer = await _repository.GetByIdAsync(request.Id);
        _repository.Delete(customer);
        await _repository.SaveChangesAsync();

        return Unit.Value;
    }
}


There are several reasons why CQRS is considered a better approach in some cases:

  • Performance and scalability: By separating the command and query components, you can optimize each component for its specific needs. The command handlers can be designed to handle high volumes of requests, while the query handlers can be designed to provide fast and efficient access to the system’s data. This can improve the overall performance and scalability of the system.
  • Modularity and separation of concerns: By separating the command and query components, you can clearly define the responsibilities of each component and reduce the complexity of the system. This can make the system easier to maintain and evolve over time.
  • Auditing and versioning: By using the CQRS pattern in combination with the Event Sourcing pattern, you can store the history of all changes to the system’s state as a sequence of events. This can be useful for auditing, debugging, and rolling back changes to the system.
  • Security and isolation: By separating the command and query components, you can apply different security and isolation measures to each component. For example, you might want to apply more stringent security measures to the command components to protect against unauthorized changes to the system’s state.

In summary, the CQRS pattern is a software design pattern that separates the responsibility of issuing commands from the responsibility of querying data. CQRS can be used to improve the performance, scalability, and reliability of a system, and can be combined with the Event Sourcing pattern to enable auditing, debugging, and versioning of the system’s state.

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Create a website or blog at WordPress.com

Up ↑