abp-dependency-rules

---
name: abp-dependency-rules
description: ABP project layer dependency rules - which projects can reference which, domain/application/infrastructure separation, cross-layer violations to avoid. Use when reviewing project structure, adding new project references, or checking if a dependency direction is correct.
---

# ABP Dependency Rules

## Core Principles (All Templates)

These principles apply regardless of solution structure:

1. **Domain logic never depends on infrastructure** (no DbContext in domain/application)
2. **Use abstractions** (interfaces) for dependencies
3. **Higher layers depend on lower layers**, never the reverse
4. **Data access through repositories**, not direct DbContext

## Layered Template Structure

> **Note**: This section applies to layered templates (app, module). Single-layer and microservice templates have different structures.

```
Domain.Shared    → Constants, enums, localization keys
       ↑
    Domain       → Entities, repository interfaces, domain services
       ↑
Application.Contracts → App service interfaces, DTOs
       ↑
  Application    → App service implementations
       ↑
   HttpApi       → REST controllers (optional)
       ↑
     Host        → Final application with DI and middleware
```

### Layered Dependency Direction

| Project | Can Reference | Referenced By |
|---------|---------------|---------------|
| Domain.Shared | Nothing | All |
| Domain | Domain.Shared | Application, Data layer |
| Application.Contracts | Domain.Shared | Application, HttpApi, Clients |
| Application | Domain, Contracts | Host |
| EntityFrameworkCore/MongoDB | Domain | Host only |
| HttpApi | Contracts only | Host |

## Critical Rules

### ❌ Never Do
```csharp
// Application layer accessing DbContext directly
public class BookAppService : ApplicationService
{
    private readonly MyDbContext _dbContext; // ❌ WRONG
}

// Domain depending on application layer
public class BookManager : DomainService
{
    private readonly IBookAppService _appService; // ❌ WRONG
}

// HttpApi depending on Application implementation
public class BookController : AbpController
{
    private readonly BookAppService _bookAppService; // ❌ WRONG - Use interface
}
```

### ✅ Always Do
```csharp
// Application layer using repository abstraction
public class BookAppService : ApplicationService
{
    private readonly IBookRepository _bookRepository; // ✅ CORRECT
}

// Domain service using domain abstractions
public class BookManager : DomainService
{
    private readonly IBookRepository _bookRepository; // ✅ CORRECT
}

// HttpApi depending on contracts only
public class BookController : AbpController
{
    private readonly IBookAppService _bookAppService; // ✅ CORRECT
}
```

## Repository Pattern Enforcement

### Interface Location
```csharp
// In Domain project
public interface IBookRepository : IRepository<Book, Guid>
{
    Task<Book> FindByNameAsync(string name);
}
```

### Implementation Location
```csharp
// In EntityFrameworkCore project
public class BookRepository : EfCoreRepository<MyDbContext, Book, Guid>, IBookRepository
{
    // Implementation
}

// In MongoDB project
public class BookRepository : MongoDbRepository<MyDbContext, Book, Guid>, IBookRepository
{
    // Implementation
}
```

## Multi-Application Scenarios

When you have multiple applications (e.g., Admin + Public API):

### Vertical Separation
```
MyProject.Admin.Application      - Admin-specific services
MyProject.Public.Application     - Public-specific services
MyProject.Domain                 - Shared domain (both reference this)
```

### Rules
- Admin and Public application layers **MUST NOT** reference each other
- Share domain logic, not application logic
- Each vertical can have its own DTOs even if similar

## Enforcement Checklist (Layered Templates)

When adding a new feature:
1. **Entity changes?** → Domain project
2. **Constants/enums?** → Domain.Shared project
3. **Repository interface?** → Domain project (only if custom queries needed)
4. **Repository implementation?** → EntityFrameworkCore/MongoDB project
5. **DTOs and service interface?** → Application.Contracts project
6. **Service implementation?** → Application project
7. **API endpoint?** → HttpApi project (if not using auto API controllers)

## Common Violations to Watch

| Violation | Impact | Fix |
|-----------|--------|-----|
| DbContext in Application | Breaks DB independence | Use repository |
| Entity in DTO | Exposes internals | Map to DTO |
| IQueryable in interface | Breaks abstraction | Return concrete types |
| Cross-module app service call | Tight coupling | Use events or domain |