If you’ve ever built an app, you’ve probably used CRUD: Create, Read, Update, Delete. It’s the bread and butter of interacting with data. But what if I told you there’s a different way to think about how your app talks to its data, especially when things get big and complicated?

Let's break it down like we're just chatting over coffee.


The Old Faithful: Traditional CRUD

Imagine your app as a single door to your database. When you want to save something, read something, change something, or delete something, you always go through that one door. This door handles everything.


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In a traditional CRUD system, you usually have:

  • One Database Schema: Your data is stored in a way that tries to be good for both writing/updating and reading.
  • One Set of APIs/Services: A single service or set of API endpoints handles all types of operations.
  • Simplicity: For smaller applications, this is awesome! It’s easy to understand, quick to set up, and very intuitive.

The Good:

  • Simple: Easy to design and implement.
  • Well Understood: Most developers are familiar with it.
  • Quick to Start: Great for building MVPs or less complex apps.

The Not-So-Good (as apps grow):

  • Performance Bottlenecks: What if reading data is super common (like product listings) but updating data is rare (like adding a new product)? If the same database schema and infrastructure handle both, one might slow down the other.
  • Complex Queries: Your read models (how you fetch data) might become very complex to get the exact data you need for a specific UI, leading to slow queries.
  • Security/Permissions: It can be tricky to apply different security rules for reading versus writing if they're handled by the same logic.
  • Scalability: Scaling a single database or service that does everything can become a headache.

The Specialized Approach: CQRS


Now, imagine your app has two separate doors to your data: one door strictly for making changes (Commands) and another door strictly for getting information (Queries).

This isn't just about having separate functions; it's about having potentially separate data models, separate databases, and even separate infrastructure, all optimized for their specific tasks.


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Here’s how CQRS breaks things down:

  1. Commands (The Write Side):
    • These are instructions to do something. "Add product to cart," "Change user password," "Process order."
    • Commands are imperative, meaning they express intent. They don't return data (usually).
    • They go through the "write" door, which is optimized for high-volume writes, consistency, and complex business logic. This might involve a transactional database, an event store, or a messaging queue.
  3. Queries (The Read Side):
    • These are requests to get information. "Show all products," "Display order history," "Find user by email."
    • Queries are declarative, meaning they express what data is needed.
    • They go through the "read" door, which is optimized for super-fast reads. This could be a denormalized database, a search index (like Elasticsearch), or a caching layer.

The Magic in the Middle: Synchronization

"But wait," you might ask, "if they're separate, how does the read side know what happened on the write side?" This is where the synchronization comes in. Typically, when a command successfully changes something on the write side, an event is published. The read side then subscribes to these events and updates its own data store to reflect the changes.


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This process is often asynchronous, which means there might be a tiny delay between when the data is written and when it appears on the read side. For many applications (like social media feeds or e-commerce sites), this brief delay is completely acceptable.


The Final Showdown: When to Use What

This isn't about one being "better" than the other; it's about choosing the right tool for the right job.

Choose CRUD When:

  • You're building a simple application or an MVP.
  • Your application has a low to moderate number of users.
  • Your read and write operations are balanced and have similar performance requirements.
  • The business logic is straightforward and a single data model works well.

Choose CQRS When:

  • You are facing significant performance issues with complex read queries.
  • Your application has a high volume of read operations compared to write operations.
  • You have distinct security requirements for your read and write models.
  • You need to scale your read and write models independently to meet high demand.
  • You have a domain with very complex business logic that benefits from an event-driven architecture.

In Summary:

  • CRUD is your reliable Swiss Army Knife: simple, effective, and good for most everyday tasks.
  • CQRS is like having a separate, specialized power tool for every job: more complex to set up, but incredibly efficient for specific, heavy-duty tasks.

The key takeaway is that you don't need to jump straight into CQRS. Start with CRUD, and if you encounter the scaling and performance challenges it presents, then CQRS becomes a powerful pattern to consider.

I hope this helped clarify a complex topic. Happy coding!