debugging-patterns

name	debugging-patterns
description	Debug .NET/ABP and React applications with systematic root cause analysis. Use when: (1) investigating bugs or errors, (2) analyzing stack traces, (3) diagnosing N+1 queries, (4) fixing async deadlocks, (5) resolving React state issues.
layer	1
tech_stack	["dotnet","csharp","typescript","react"]
topics	["root-cause-analysis","stack-traces","logging","profiling","breakpoints"]
depends_on	[]
complements	["error-handling-patterns"]
keywords	["Debug","StackTrace","Logging","Profiler","Breakpoint","Exception","NullReference"]

Debugging Patterns

Systematic debugging patterns for ABP Framework and React applications.

When to Use

• Investigating bugs or test failures
• Analyzing stack traces and error messages
• Diagnosing database query issues (N+1, tracking conflicts)
• Fixing async/await deadlocks
• Resolving React state management bugs

Debugging Process

1. Capture Information

• Error message and full stack trace
• Reproduction steps (reliable vs intermittent)
• Environment (dev/staging/prod)
• Recent code changes

2. Isolate the Problem

• Identify failing component (backend/frontend)
• Narrow down to specific file/function
• Check logs and network requests

3. Form Hypothesis

• Match error pattern to known issues
• Check similar past issues
• Review recent commits

4. Verify and Fix

• Test hypothesis with minimal change
• Verify fix doesn't break other things
• Add test to prevent regression

ABP Framework Issues

Authorization Failure

Error: Authorization failed for the request

Diagnosis Checklist:

1. Is permission defined in {Project}Permissions.cs?
2. Is permission granted to role in PermissionDefinitionProvider?
3. Is [Authorize] attribute using correct permission constant?

// Check permission definition
public static class ClinicPermissions
{
    public static class Patients
    {
        public const string Default = "Clinic.Patients";
        public const string Create = "Clinic.Patients.Create"; // Missing?
    }
}

// Check attribute matches
[Authorize(ClinicPermissions.Patients.Create)]  // Not .Default
public async Task<PatientDto> CreateAsync(...)

Entity Not Found

Error: Entity of type Patient with id X was not found

Diagnosis:

// Debug: Verify entity exists
var exists = await _repository.AnyAsync(x => x.Id == id);
_logger.LogDebug("Patient {Id} exists: {Exists}", id, exists);

// Fix: Use FirstOrDefaultAsync for graceful handling
var patient = await _repository.FirstOrDefaultAsync(x => x.Id == id);
if (patient == null)
{
    throw new UserFriendlyException("Patient not found");
}

Async Deadlock

Symptom: Application hangs, no error message

Cause: Using .Result or .Wait() on async code

// BAD: Causes deadlock in ASP.NET Core
var result = _service.GetAsync(id).Result;
var result2 = _service.GetAsync(id).Wait();

// GOOD: Proper async/await
var result = await _service.GetAsync(id);

Entity Framework Core Issues

N+1 Query Problem

Symptom: Slow API response, excessive database queries in logs

Diagnosis: Enable EF Core logging

{
  "Logging": {
    "LogLevel": {
      "Microsoft.EntityFrameworkCore.Database.Command": "Information"
    }
  }
}

// BAD: N+1 queries - executes 1 + N queries
var patients = await _repository.GetListAsync();
foreach (var patient in patients)
{
    var appointments = patient.Appointments; // Lazy load each time!
}

// GOOD: Eager loading with Include
var patients = await _repository
    .WithDetailsAsync(p => p.Appointments);

// BETTER: Project to DTO
var patients = await query
    .Select(p => new PatientDto
    {
        Id = p.Id,
        AppointmentCount = p.Appointments.Count
    })
    .ToListAsync();

Tracking Conflict

Error: The instance of entity type cannot be tracked

Cause: Entity with same key already tracked

// Fix: Use AsNoTracking for read-only queries
var patient = await _repository
    .AsNoTracking()
    .FirstOrDefaultAsync(p => p.Id == id);

React/TypeScript Issues

Stale Closure

Symptom: State shows old value in callback

// BAD: Stale closure - always uses initial count
const [count, setCount] = useState(0);
useEffect(() => {
  const interval = setInterval(() => {
    setCount(count + 1); // Captures initial count = 0
  }, 1000);
  return () => clearInterval(interval);
}, []); // Empty deps = stale closure

// GOOD: Functional update
setCount(prev => prev + 1);

React Query Cache Not Updating

Symptom: Data not refreshing after mutation

// BAD: Cache not invalidated
const createMutation = useMutation(createPatient);

// GOOD: Invalidate on success
const queryClient = useQueryClient();
const createMutation = useMutation(createPatient, {
  onSuccess: () => {
    queryClient.invalidateQueries(['patients']);
  }
});

TypeScript Any Leak

Symptom: Runtime type errors despite compilation success

// Diagnosis: Search for any types
// grep ": any" or "as any"

// Fix: Add explicit types
interface ApiResponse<T> {
  data: T;
  success: boolean;
  error?: string;
}

Debug Commands

# Backend: Run with verbose logging
dotnet run --project api/src/ClinicManagementSystem.HttpApi.Host 2>&1 | grep -i error

# Backend: Run specific failing test
dotnet test --filter "FullyQualifiedName~PatientAppService_Tests"

# EF Core: See generated SQL (in appsettings.Development.json)
# "Microsoft.EntityFrameworkCore.Database.Command": "Information"

# Frontend: Browser DevTools
# Console tab: JavaScript errors
# Network tab > XHR: API requests/responses

Output Format

## Bug Analysis: [Issue Title]

### Symptoms
- [What was observed]

### Root Cause
[Technical explanation of why this happened]

### Evidence

[Stack trace or log excerpt]

### Fix
```csharp
// Before
[problematic code]

// After
[fixed code]

Verification

• Unit test passes
• Manual test passes
• No regression

Prevention

[How to prevent this in the future]

## Integration Points

This skill is used by:
- **debugger**: Root cause analysis and diagnosis
- **abp-code-reviewer**: Identifying potential issues in backend PRs
- **abp-developer**: Fixing bugs during implementation