Typorithm · easy

Layered (N-Tier)

layered-architecturearchitecturelayersseparation-of-concernsdependencies

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Full lesson · 8 learning steps Open any exercise for focused practice

Step 1 of 8 · intro card

Learn Layered (N-Tier)

Layered & Clean

Layered architecture stacks presentation over application/service over domain over data. Each layer depends only on the layer directly below it, so requests flow top-down and concerns stay separated.

An N-tier app is sliced into horizontal layers: presentation (controllers), application/service (use cases), domain (business rules), and data (persistence).

Dependencies point strictly downward — a controller knows the service, a service knows the repository, but no lower layer ever reaches up to a higher one.

Because each layer talks only to the one beneath it, you can change the database or swap the UI without rewriting the layers in between.

Layers stack: presentation -> service -> domain -> data.

Each layer depends only on the one directly below.

Dependencies and request flow both point downward.

class OrderController {
  constructor(private service: OrderService) {}
  create(req) {
    return this.service.place(req.body);
  }
}

class OrderService {
  constructor(private repo: OrderRepository) {}
  place(order) {
    return this.repo.save(order);
  }
}

Read the implementation

Connect each part of the code to the concept before you type.

1. Presentation layer

The controller is the presentation layer; it accepts the request and delegates downward.

class OrderController {

2. Depends on the layer below

The controller holds a service, never the other way round — dependencies point downward.

constructor(private service: OrderService) {}

3. Service layer

The service layer holds business logic, isolated from HTTP details above it.

class OrderService {

4. Calls the data layer

The service delegates persistence to the repository — the data layer one tier below.

return this.repo.save(order);

A complete learning loop

Understand

Read the concept map and follow the code breakdown.

Reconstruct

Type the implementation, repair mistakes and work through every recall exercise.

Verify

Use the final check without hints; revisit weak concepts in short practice sessions.