Dart
Repository
Learn the repository pattern.
Repository
The Repository pattern abstracts data access. The domain layer defines a Repository interface; the data layer implements it. The domain does not know whether data comes from an API or a database.
Example: abstract class ProductRepository { Product fetch(String id); }. Concrete classes: ApiProductRepository, DbProductRepository, MockProductRepository — all implement the same interface.
Advantage: in tests MockProductRepository is used; domain logic is tested without hitting a real API. When the data source changes, only the concrete class changes.
Multiple data sources
The same interface can be implemented by multiple classes: ApiRepo (remote API), DbRepo (local database), CacheRepo (cache). The application decides which to use via configuration.
Cache strategy: CacheRepo checks the cache first; on a miss it falls back to ApiRepo and writes the result to the cache. This is known as the decorator pattern.
The repository interface stays unchanged while the inner implementation can be swapped freely. This makes the code easier to maintain and extend.
Exercise Define ProductRepository and a Mock
Define a Product class with final String id; final String name; Product(this.id, this.name);. Define an abstract class ProductRepository with Product fetch(String id);. Define a class MockProductRepository implements ProductRepository with @override Product fetch(String id) => Product(id, 'Kitap');. In main create final repo = MockProductRepository();; add final product = repo.fetch('1'); and print(product.name);.
Show example solution
class Product {
final String id;
final String name;
Product(this.id, this.name);
}
abstract class ProductRepository {
Product fetch(String id);
}
class MockProductRepository implements ProductRepository {
@override
Product fetch(String id) => Product(id, 'Kitap');
}
void main() {
final repo = MockProductRepository();
final product = repo.fetch('1');
print(product.name);
}
Test yourself
-
Match the repository parts
- Repository
- Contract
- RepositoryImpl
- Implementation
- fetch(id)
- Read method
- save(entity)
- Write method
-
What does the Repository pattern abstract?
- UI drawing
- Data access
- Running tests
- File reading
Show answer
Data access — the Repository abstracts data access; the source stays hidden.
-
Repository implementation
class ApiUserRepository ____ UserRepository { }
Show answer
class ApiUserRepository implements UserRepository { }
Next lesson: Dependency injection
