pgsql-jellyfin/docs/ASYNC_CONVERSION_CHECKLIST.md

Repository Async Conversion Checklist

Use this checklist when converting a repository class from synchronous to asynchronous operations.

📋 Pre-Conversion Checklist

• Identify all public methods in the repository interface
• Check for method dependencies - what calls these methods?
• Review current tests - ensure you understand expected behavior
• Create a feature branch for the conversion
• Document breaking changes for consumers

🔄 Conversion Steps

Step 1: Update Interface Definition

File: MediaBrowser.Controller\Persistence\I[RepositoryName].cs

• Add using System.Threading.Tasks;
• Add CancellationToken parameter to all methods
• Change return types:
  • void → Task
  • T → Task<T>
  • IEnumerable<T> → IAsyncEnumerable<T> (for streaming) or Task<List<T>>
• Rename methods to include Async suffix
• Add XML documentation for cancellation token

Example:

// BEFORE
void SaveUser(User user);
User? GetUser(Guid id);
IEnumerable<User> GetAllUsers();

// AFTER
Task SaveUserAsync(User user, CancellationToken cancellationToken = default);
Task<User?> GetUserAsync(Guid id, CancellationToken cancellationToken = default);
Task<List<User>> GetAllUsersAsync(CancellationToken cancellationToken = default);
// OR for streaming:
IAsyncEnumerable<User> GetAllUsersAsync(CancellationToken cancellationToken = default);

Step 2: Update Implementation

File: [Project]\[RepositoryName].cs

2.1 Method Signatures

• Add async modifier to method declarations
• Change return type to Task or Task<T>
• Add CancellationToken parameter

2.2 Database Context Usage

• Change using to await using for DbContext

  // BEFORE: using var context = _dbProvider.CreateDbContext();
  // AFTER:  await using var context = _dbProvider.CreateDbContext();
  

2.3 Transaction Handling

• BeginTransaction() → BeginTransactionAsync(cancellationToken)
• Commit() → CommitAsync(cancellationToken)
• Rollback() → RollbackAsync(cancellationToken)
• Change using to await using for transactions

2.4 Query Operations

• ToList() → ToListAsync(cancellationToken)
• ToArray() → ToArrayAsync(cancellationToken)
• ToDictionary() → ToDictionaryAsync(cancellationToken)
• FirstOrDefault() → FirstOrDefaultAsync(cancellationToken)
• First() → FirstAsync(cancellationToken)
• SingleOrDefault() → SingleOrDefaultAsync(cancellationToken)
• Single() → SingleAsync(cancellationToken)
• Any() → AnyAsync(cancellationToken)
• Count() → CountAsync(cancellationToken)
• LongCount() → LongCountAsync(cancellationToken)
• Sum() → SumAsync(cancellationToken)
• Average() → AverageAsync(cancellationToken)
• Min() → MinAsync(cancellationToken)
• Max() → MaxAsync(cancellationToken)

2.5 Command Operations

• SaveChanges() → SaveChangesAsync(cancellationToken)
• ExecuteDelete() → ExecuteDeleteAsync(cancellationToken)
• ExecuteUpdate() → ExecuteUpdateAsync(cancellationToken)
• Add() - no async version, but SaveChanges must be async
• Remove() - no async version, but SaveChanges must be async
• Update() - no async version, but SaveChanges must be async

2.6 Navigation Properties

• .Load() → .LoadAsync(cancellationToken)
• .Entry().Collection().Load() → .Entry().Collection().LoadAsync(cancellationToken)
• .Include() - works with async, no change needed

2.7 ForEach Loops

• Convert to await foreach for IAsyncEnumerable

  // BEFORE
  foreach (var item in items)
  {
      // process
  }
  
  // AFTER
  await foreach (var item in items.WithCancellation(cancellationToken))
  {
      // process
  }
  

2.8 Helper Methods

• Convert all private helper methods that use database to async
• Propagate async/await through call chain

Step 3: Update Consumers

3.1 Service Layer

• Update service interfaces to use Task return types
• Update service implementations to use await
• Add CancellationToken parameters

3.2 API Controllers

• Add async Task<ActionResult> to controller methods
• Add CancellationToken parameter (ASP.NET Core will inject it)
• Use await when calling services

Example:

[HttpGet("{id}")]
public async Task<ActionResult<UserDto>> GetUser(
    [FromRoute] Guid id,
    CancellationToken cancellationToken)
{
    var user = await _userRepository.GetUserAsync(id, cancellationToken);
    return user is null ? NotFound() : Ok(_mapper.Map<UserDto>(user));
}

3.3 Background Services

• Ensure ExecuteAsync properly awaits all operations
• Pass cancellation token through the chain

Step 4: Update Tests

4.1 Test Method Signatures

• Change test methods to async Task
• Add await before repository calls

4.2 Mock Setup

• Update mocks to return Task or Task<T>

  // BEFORE
  _mockRepository.Setup(x => x.GetUser(It.IsAny<Guid>()))
      .Returns(user);
  
  // AFTER
  _mockRepository.Setup(x => x.GetUserAsync(It.IsAny<Guid>(), It.IsAny<CancellationToken>()))
      .ReturnsAsync(user);
  

4.3 Test Assertions

• Use await for async operations in assertions
• Test cancellation scenarios

Example Test:

[Fact]
public async Task GetUserAsync_ValidId_ReturnsUser()
{
    // Arrange
    var userId = Guid.NewGuid();
    var expectedUser = new User { Id = userId };
    _mockRepository
        .Setup(x => x.GetUserAsync(userId, It.IsAny<CancellationToken>()))
        .ReturnsAsync(expectedUser);
    
    // Act
    var result = await _service.GetUserAsync(userId, CancellationToken.None);
    
    // Assert
    Assert.NotNull(result);
    Assert.Equal(userId, result.Id);
}

[Fact]
public async Task GetUserAsync_Cancelled_ThrowsOperationCanceledException()
{
    // Arrange
    var cts = new CancellationTokenSource();
    cts.Cancel();
    
    // Act & Assert
    await Assert.ThrowsAsync<OperationCanceledException>(
        () => _service.GetUserAsync(Guid.NewGuid(), cts.Token)
    );
}

🔍 Code Review Checklist

Before submitting PR:

• All synchronous database operations converted
• CancellationToken passed through entire call chain
• No Task.Result or .Wait() calls (causes deadlocks)
• No async void methods (except event handlers)
• Proper ConfigureAwait(false) usage in library code (optional in ASP.NET Core)
• All tests updated and passing
• No performance regressions
• Memory usage acceptable
• Documentation updated

⚡ Performance Optimization Opportunities

Consider these optimizations during conversion:

1. Parallel Operations

When operations are independent, use Task.WhenAll:

// Sequential (slow)
await DeleteAncestorsAsync(id, cancellationToken);
await DeleteImagesAsync(id, cancellationToken);
await DeleteChaptersAsync(id, cancellationToken);

// Parallel (fast)
await Task.WhenAll(
    DeleteAncestorsAsync(id, cancellationToken),
    DeleteImagesAsync(id, cancellationToken),
    DeleteChaptersAsync(id, cancellationToken)
);

2. Streaming Results

For large result sets, use IAsyncEnumerable<T>:

public async IAsyncEnumerable<User> GetAllUsersAsync(
    [EnumeratorCancellation] CancellationToken cancellationToken = default)
{
    await using var context = _dbProvider.CreateDbContext();
    
    await foreach (var user in context.Users.AsAsyncEnumerable()
        .WithCancellation(cancellationToken))
    {
        yield return user;
    }
}

3. Batch Operations

Use ExecuteUpdateAsync / ExecuteDeleteAsync instead of loading then saving:

// Slow - loads all into memory
var items = await context.Items.Where(x => x.IsOld).ToListAsync();
context.Items.RemoveRange(items);
await context.SaveChangesAsync();

// Fast - executes in database
await context.Items
    .Where(x => x.IsOld)
    .ExecuteDeleteAsync(cancellationToken);

🐛 Common Pitfalls to Avoid

❌ DON'T: Use Task.Result or .Wait()

// WRONG - causes deadlocks
var user = GetUserAsync(id).Result;

❌ DON'T: Forget cancellation token

// WRONG - can't cancel long-running operations
public async Task<User> GetUserAsync(Guid id)
{
    return await context.Users.FirstOrDefaultAsync(x => x.Id == id);
}

❌ DON'T: Use async void

// WRONG - exceptions can't be caught
public async void SaveUser(User user) { }

✅ DO: Proper async pattern

// CORRECT
public async Task<User?> GetUserAsync(Guid id, CancellationToken cancellationToken = default)
{
    await using var context = _dbProvider.CreateDbContext();
    return await context.Users
        .FirstOrDefaultAsync(x => x.Id == id, cancellationToken);
}

📝 Commit Message Template

feat(repository): Convert [RepositoryName] to async

- Updated I[RepositoryName] interface with async signatures
- Converted all database operations to async/await
- Added CancellationToken support throughout
- Updated all tests to async
- Updated consumers in service and controller layers

BREAKING CHANGE: All [RepositoryName] methods are now async and require await.
Migration guide: [link to documentation]

Closes #[issue-number]

🎯 Success Criteria

• All tests passing
• No compiler warnings
• Code coverage maintained or improved
• No performance regressions
• Documentation updated
• Migration guide provided
• Breaking changes documented