Example usage of async command/query implementation

Example.cs

public class FetchUserByEmailQuery : IQuery<User>
{
    private readonly string email;

    public FetchUserByEmailQuery(string email)
    {
        this.email = email;
    }

    public async Task<User> ExecuteAsync(IDbConnection db)
    {
        return db.QueryAsync<User>("select * from [User] where [Email] = @email", new { email }).FirstOrDefault();
    }
}

public class CreateUserCommand : ICommand
{
    private readonly User user;

    public CreateUserCommand(User user)
    {
        this.user = user;
    }

    public async Task ExecuteAsync(IDbConnection db)
    {
        await db.ExecuteAsync("insert into [User] ([Email]) values (@Email)", user);
    }
}

public class UserController
{
    private readonly IDatabase db;

    public UserController(IDatabase db)
    {
        this.db = db;
    }

    public async Task Create(string email)
    {
        // See if the user exists
        var user = await db.ExecuteAsync(new FetchUserByEmailQuery(email));

        if (user == null)
        {
            // If not, create it
            user = new User { Email = email };
            await db.ExecuteAsnyc(new CreateUserCommand(user));
        }
    }
}