Layered Architecture (Controllers, Services, Models) in Node.js
As Node.js applications grow in complexity, a well-defined code structure becomes indispensable.
The layered architecture, often seen as an adaptation of the Model-View-Controller (MVC) pattern for APIs and backends, is a recommended practice that promotes separation of concerns.
This improves code maintainability, scalability, and readability, making your application more robust and easier to collaborate on as a team.
Synopsis:
In a typical layered architecture for Node.js (especially with Express), we primarily distinguish three layers: Controllers, Services, and Models. Each has a specific role and communicates with adjacent layers in a controlled manner.
- 1. Controllers Layer:
Controllers are the "brain" of client interaction. They are responsible for receiving HTTP requests, validating basic input data, coordinating business logic (delegating to the services layer), and sending the appropriate HTTP response to the client. They should not contain complex business logic or interact directly with the database.
- Responsibilities:
- Parse the request (headers, body, query params).
- Basic validation of input data (e.g., format).
- Call appropriate methods in the services layer.
- Handle errors and send HTTP responses with correct status codes.
- Responsibilities:
- 2. Services Layer (Business Logic):
The services layer (also known as the business logic layer) is the heart of the application. It contains business rules, complex logic, and the orchestration of operations involving multiple models. Services are HTTP agnostic; that is, they do not know or care about req or res.
- Responsibilities:
- Implement application-specific business logic.
- Perform more complex business validations.
- Coordinate database operations (delegating to models).
- Transform data between models and the format the controller needs.
- Responsibilities:
- 3. Models Layer (Data Access):
The models layer interacts directly with the database. Each model represents an entity or collection of data in your database and provides methods for performing CRUD (Create, Read, Update, Delete) and other persistence operations. An ORM (Object-Relational Mapper) like Sequelize for relational databases or an ODM (Object-Document Mapper) like Mongoose for MongoDB is often used.
- Responsibilities:
- Define the data structure (schemas).
- Handle database-level validation.
- Interact directly with the database (queries, insertions, etc.).
- Provide methods to access and manipulate data.
- Responsibilities:
Request Flow and Benefits:
The flow of an HTTP request in an application with this architecture would be:
- Route/Endpoint: Receives the request and directs it to the appropriate Controller.
- Controller: Validates the input, calls one or more Services.
- Service: Contains the business logic, calls one or more Models.
- Model: Interacts with the database and returns the data to the Service.
- Service: Processes the data from the Model and returns it to the Controller.
- Controller: Formats the response and sends it back to the client.
Benefits:
- Separation of Concerns (SOC): Each layer has a clear and defined purpose, which reduces complexity.
- Maintainability: Changes in one layer (e.g., changing the database) have minimal impact on other layers.
- Scalability: It is easier to scale specific parts of the application, as they are decoupled.
- Ease of Testing: With separated logic, it is much simpler to write unit tests for each layer.
- Collaboration: Different teams or developers can work on different layers simultaneously.
Adopting a layered architecture from the start will save you many headaches as your Node.js application grows, transforming a spaghetti project into a clean and manageable codebase.
Exercises
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