# Command Registration

How to register command handlers in dependency injection.

## Basic Registration

### Command with Result

```csharp
builder.Services.AddCommand<CreateUserCommand, int, CreateUserCommandHandler>();
```

**This registers:**
- Handler as `ICommandHandler<CreateUserCommand, int>`
- Metadata for endpoint discovery
- Scoped lifetime (default)

### Command without Result

```csharp
builder.Services.AddCommand<DeleteUserCommand, DeleteUserCommandHandler>();
```

## Registration with Validator

```csharp
builder.Services.AddCommand<CreateUserCommand, int, CreateUserCommandHandler, CreateUserCommandValidator>();
```

**This registers:**
- Handler
- Validator as `IValidator<CreateUserCommand>`
- Metadata

## Registration with Workflow

```csharp
builder.Services.AddCommandWithWorkflow<CreateUserCommand, int, UserWorkflow, CreateUserCommandHandler>();
```

For event-emitting commands.

## Service Lifetimes

### Scoped (Default - Recommended)

```csharp
services.AddCommand<CreateUserCommand, int, CreateUserCommandHandler>();
// Handler is Scoped
```

**Characteristics:**
- One instance per request
- Can inject DbContext
- Disposed after request

### Custom Lifetime

```csharp
// Transient
services.AddTransient<ICommandHandler<CreateUserCommand, int>, CreateUserCommandHandler>();

// Singleton (not recommended - can't inject DbContext)
services.AddSingleton<ICommandHandler<CreateUserCommand, int>, CreateUserCommandHandler>();
```

## Bulk Registration

### Extension Methods

```csharp
// Extensions/ServiceCollectionExtensions.cs
public static class ServiceCollectionExtensions
{
    public static IServiceCollection AddUserCommands(this IServiceCollection services)
    {
        services.AddCommand<CreateUserCommand, int, CreateUserCommandHandler, CreateUserCommandValidator>();
        services.AddCommand<UpdateUserCommand, UpdateUserCommandHandler, UpdateUserCommandValidator>();
        services.AddCommand<DeleteUserCommand, DeleteUserCommandHandler>();
        return services;
    }

    public static IServiceCollection AddOrderCommands(this IServiceCollection services)
    {
        services.AddCommand<PlaceOrderCommand, int, PlaceOrderCommandHandler>();
        services.AddCommand<CancelOrderCommand, CancelOrderCommandHandler>();
        return services;
    }
}

// Usage in Program.cs
builder.Services.AddUserCommands();
builder.Services.AddOrderCommands();
```

### Module Pattern

```csharp
public interface IModule
{
    void RegisterServices(IServiceCollection services);
}

public class UserModule : IModule
{
    public void RegisterServices(IServiceCollection services)
    {
        // Commands
        services.AddCommand<CreateUserCommand, int, CreateUserCommandHandler>();
        services.AddCommand<UpdateUserCommand, UpdateUserCommandHandler>();

        // Queries
        services.AddQuery<GetUserQuery, UserDto, GetUserQueryHandler>();

        // Services
        services.AddScoped<IUserRepository, UserRepository>();
    }
}

// Auto-register all modules
var modules = typeof(Program).Assembly
    .GetTypes()
    .Where(t => typeof(IModule).IsAssignableFrom(t) && !t.IsInterface)
    .Select(Activator.CreateInstance)
    .Cast<IModule>();

foreach (var module in modules)
{
    module.RegisterServices(builder.Services);
}
```

## Organizing Registrations

### By Feature

```
Program.cs
Extensions/
  UserServiceRegistration.cs
  OrderServiceRegistration.cs
  ProductServiceRegistration.cs
```

### By Layer

```
Program.cs
Extensions/
  CommandRegistration.cs
  QueryRegistration.cs
  RepositoryRegistration.cs
```

## See Also

- [Dependency Injection](../../architecture/dependency-injection.md) - DI patterns
- [Modular Solution Structure](../../architecture/modular-solution-structure.md)