Service Patterns

Overview

Services contain all business logic. They are the heart of the application, orchestrating operations between controllers and data access.

Service Structure

Interface-Based Design

Always define an interface for each service:

public interface ITaskService
{
    Task<List<TaskResponse>> GetAllAsync(CancellationToken cancellationToken = default);
    Task<TaskResponse?> GetByIdAsync(Guid id, CancellationToken cancellationToken = default);
    Task<TaskResponse> CreateAsync(CreateTaskRequest request, CancellationToken cancellationToken = default);
    Task<TaskResponse?> UpdateAsync(Guid id, UpdateTaskRequest request, CancellationToken cancellationToken = default);
    Task<bool> DeleteAsync(Guid id, CancellationToken cancellationToken = default);
}

Primary Constructor for DI

public class TaskService(ITaskRepository repository, ILogger<TaskService> logger) : ITaskService
{
    // Implementation
}

ServiceResult Pattern

For operations that can fail in expected ways, use a result pattern:

public record ServiceResult<T>
{
    public bool IsSuccess { get; init; }
    public T? Value { get; init; }
    public string? Error { get; init; }
    public ServiceErrorType? ErrorType { get; init; }

    public static ServiceResult<T> Success(T value) => new() { IsSuccess = true, Value = value };
    public static ServiceResult<T> NotFound(string error) => new() { IsSuccess = false, Error = error, ErrorType = ServiceErrorType.NotFound };
    public static ServiceResult<T> ValidationError(string error) => new() { IsSuccess = false, Error = error, ErrorType = ServiceErrorType.Validation };
}

public enum ServiceErrorType
{
    NotFound,
    Validation,
    Conflict,
    Forbidden
}

Business Logic Encapsulation

All Logic in Services

// Good - business rules in service
public async Task<TaskResponse> CreateAsync(CreateTaskRequest request, CancellationToken cancellationToken)
{
    var task = new TaskItem
    {
        Id = Guid.NewGuid(),
        Title = request.Title.Trim(),
        Description = request.Description?.Trim(),
        Status = TaskStatus.Pending,
        CreatedAt = DateTime.UtcNow
    };

    // Business rule: Set default due date if not provided
    task.DueDate ??= DateTime.UtcNow.AddDays(7);

    await repository.CreateAsync(task, cancellationToken);
    logger.LogInformation("Created task {TaskId} with title {Title}", task.Id, task.Title);

    return MapToResponse(task);
}

Never in Controllers

Controllers should only:

1. Accept HTTP request
2. Call service
3. Return HTTP response

Structured Logging

Use Semantic Logging

// Good - structured with named parameters
logger.LogInformation("Created task {TaskId} with title {Title}", task.Id, task.Title);
logger.LogWarning("Task {TaskId} not found for update", id);
logger.LogError(ex, "Failed to delete task {TaskId}", id);

// Bad - string interpolation
logger.LogInformation($"Created task {task.Id} with title {task.Title}");

Log Levels

• LogDebug - Detailed info for debugging
• LogInformation - General operational events
• LogWarning - Unexpected but handled situations
• LogError - Errors that need attention

Error Handling

Let Exceptions Bubble for Unexpected Errors

// Don't catch unexpected exceptions in services
public async Task<TaskResponse> CreateAsync(CreateTaskRequest request, CancellationToken cancellationToken)
{
    // If repository.CreateAsync throws, let it propagate
    // Global exception handler will log and return 500
    var task = new TaskItem { /* ... */ };
    await repository.CreateAsync(task, cancellationToken);
    return MapToResponse(task);
}

Mapping

Private Mapping Methods

public class TaskService(ITaskRepository repository, ILogger<TaskService> logger) : ITaskService
{
    // Service methods...

    private static TaskResponse MapToResponse(TaskItem task) => new(
        task.Id,
        task.Title,
        task.Description,
        task.Status == TaskStatus.Completed,
        task.CreatedAt
    );

    private static List<TaskResponse> MapToResponse(IEnumerable<TaskItem> tasks) =>
        tasks.Select(MapToResponse).ToList();
}

Service Registration

Register services in Program.cs:

builder.Services.AddScoped<ITaskService, TaskService>();
builder.Services.AddScoped<ITaskRepository, JsonTaskRepository>();