Contains business logic
Backend & Runtime / Knowledge library
Repository Pattern
Provides collection-like access to domain objects backed by persistence
Why learn Repository Pattern?
It isolates domain logic from query and storage mechanics
The problem it solves
It centralizes data access boundaries for aggregate objects
Where it came from
Repository Pattern is a software design pattern that provides collection-like access to domain objects backed by persistence. Its guarantees and tradeoffs depend on the concrete implementation and operating context.
Build your understanding
Work through these exercises in order. Try the task before opening a reference.
- Define Repository Pattern and distinguish it from a neighboring concept.
- Choose a realistic task where Repository Pattern is appropriate.
- Identify a failure mode caused by misusing Repository Pattern.
- Interpret a small design or result involving Repository Pattern.
- Explain one tradeoff or limitation of Repository Pattern.
Documentation and sources
- Patterns of Enterprise Application Architecture (martinfowler.com)
Connect the ideas
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Real World Example
Inventory Management Decoupling
A regional logistics firm managing a complex warehouse inventory system.
The business problem
The business logic is tightly coupled to specific database queries, making it difficult to swap storage backends or perform unit testing without a live database connection.
How this topic solves it
The Repository pattern mediates between the domain and data mapping layers by providing a collection-like interface for accessing domain objects, effectively hiding the underlying persistence mechanism.
- Define a domain interface that exposes methods like Add, Remove, and FindById.
- Implement the interface using a specific data access technology like an ORM or direct SQL.
- Inject the repository interface into the business services to decouple logic from storage.
- Use the repository to retrieve domain objects as if they were stored in an in-memory collection.
Explains how the Domain layer interacts with the Repository interface rather than the database directly.
Defines collection-like methods
Translates to SQL/ORM calls
Persistence storage
- Domain Service → calls → Repository Interface
- Repository Implementation → implements → Repository Interface
- Repository Implementation → queries → Database
Expected business outcome
The domain layer remains agnostic of the database schema, allowing for easier testing and future infrastructure migrations.
Limitations and checks
The primary limitation is the risk of leaking database-specific performance concerns into the domain layer if the repository interface becomes too granular or complex. You can check for this by reviewing if domain services are forced to handle database-specific exceptions or pagination logic.