dependency injection MVVM Repository pattern with unit of work and MySQL Database -- Implementation guide?

[ARogala]

Hi and thanks for taking the time to read this. I am new to Avalonia but do have some experience with ASP NET core web MVC. Anyway, the title says its all. I have redone the ToDo list sample from your documentation, added in Reactive toolkit, and tried my best to implement MVVM with DI and Repository pattern + UnitOfWork with a MYSQL Database (Using Dapper as well). Just looking for guidance on if my implementation is correct. So here goes. I will post enough code below and then ask the few questions that i have. I will leave out all my Repository interfaces and UnitOfWork class because I can ask my questions without them. But i can host the repo on GitHub if anyone wants the full code?

ServiceCollectionExtensions.cs

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using MySqlConnector;
using ToDoReactive.Repository;
using ToDoReactive.Repository.IRepository;
using ToDoReactive.ViewModels;

namespace ToDoReactive.Services
{
    public static class ServiceCollectionExtensions
    {
        public static void AddCommonServices(this IServiceCollection collection)
        {

            //appsettings.json
            IConfiguration config = new ConfigurationBuilder()
           .AddJsonFile("appsettings.json")
           .Build();

            // Get a configuration section
            IConfigurationSection section = config.GetSection("ConnectionStrings");

            collection.AddMySqlDataSource(section["DefaultConnection"]);
            collection.AddSingleton<IUnitOfWork, UnitOfWork>();
            collection.AddTransient<MainWindowViewModel>();
        }
    }
}

App.axaml.cs

using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Markup.Xaml;
using Microsoft.Extensions.DependencyInjection;
using ToDoReactive.Services;
using ToDoReactive.ViewModels;
using ToDoReactive.Views;

namespace ToDoReactive
{
    public partial class App : Application
    {
        public override void Initialize()
        {
            AvaloniaXamlLoader.Load(this);
        }

        public override void OnFrameworkInitializationCompleted()
        {
            // Register all the services needed for the application to run
            ServiceCollection collection = new ServiceCollection();
            collection.AddCommonServices();
            // Creates a ServiceProvider containing services from the provided IServiceCollection
            var services = collection.BuildServiceProvider();

            var vm = services.GetRequiredService<MainWindowViewModel>();
            if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
            {
                desktop.MainWindow = new MainWindow
                {
                    DataContext = vm,
                };
            }

            base.OnFrameworkInitializationCompleted();
        }

    }
}

In Models folder i have ToDoITem.cs and ToDoItemMethods.cs

using System.ComponentModel.DataAnnotations.Schema;
using System.ComponentModel.DataAnnotations;

namespace ToDoReactive.Models
{
    [Table("to_do_list")]
    public class ToDoItem
    {

        public ToDoItem(bool isChecked, string content, int? id = null) 
        { 
            IsChecked = isChecked;
            Content = content;
            Id = id;
        }
        public ToDoItem() { }

        [Key]
        [Column("Id")]
        public int? Id { get; set; }

        [Column("IsChecked")]
        public bool IsChecked { get; set; }

        [Column("Content")]
        public string? Content { get; set; }

    }
}

using System.Collections.Generic;
using System.Threading.Tasks;
using ToDoReactive.Repository.IRepository;

namespace ToDoReactive.Models
{
    public class ToDoItemMethods
    {
        private readonly IUnitOfWork _unitOfWork;
        public ToDoItemMethods(IUnitOfWork unitOfWork) 
        {
            _unitOfWork = unitOfWork;
        }

        public async Task<bool> AddToDo(ToDoItem item)
        {
            bool success = await _unitOfWork.ToDoList.Add(item);
            return success;
        }

        public async Task<List<ToDoItem>> GetAllToDo()
        {
            return (List<ToDoItem>)await _unitOfWork.ToDoList.GetAll();
        }

        public async Task<bool> Delete(int? id) 
        { 
            if(id == null)
            {
                return false;
            }
            return await _unitOfWork.ToDoList.Delete(id);
        }

        public async Task<bool> DeleteAll()
        {
            return await _unitOfWork.ToDoList.DeleteAll();
        }

        public async Task<bool> Update(ToDoItem item)
        {
            return await _unitOfWork.ToDoList.Update(item);
        }
    }
}

ToDoItemViewModel.cs

using ReactiveUI;

namespace ToDoReactive.ViewModels
{
	public class ToDoItemViewModel : ViewModelBase
	{
		private bool _isChecked;
		private string? _content;
		private int? _id;

		public int? Id
		{
			get => _id;
			set => this.RaiseAndSetIfChanged(ref _id, value);
		}
		public string? Content
		{
			get => _content;
			set => this.RaiseAndSetIfChanged(ref _content, value);
		}

		public bool IsChecked
		{
			get => _isChecked;
			set => this.RaiseAndSetIfChanged(ref _isChecked, value);
		}
	}
}

And MainWindowViewModel.cs -- (My DI is working so guess i set that up correctly)

using ReactiveUI;
using System;
using System.Collections.ObjectModel;
using System.Collections.Generic;
using System.Reactive;
using ToDoReactive.Models;
using ToDoReactive.Repository.IRepository;
using System.Diagnostics;

namespace ToDoReactive.ViewModels
{
    public class MainWindowViewModel : ViewModelBase
    {
        private readonly IUnitOfWork _unitOfWork;
        private readonly ToDoItemMethods _toDoItemMethods;
        public MainWindowViewModel(IUnitOfWork unitOfWork) 
        {
            _unitOfWork = unitOfWork;
            _toDoItemMethods = new ToDoItemMethods(_unitOfWork);
            IObservable<bool> CanAddItem = this.WhenAnyValue(
                    x => x.NewItemContent,
                    x => !string.IsNullOrEmpty(x) && x.Length >= 3 
                );
            AddItemCommand = ReactiveCommand.Create(() => 
            {
                AddItem();
            },CanAddItem);

            RemoveItemCommand = ReactiveCommand.Create((ToDoItemViewModel item) => { 
                RemoveItem(item);
            });

            RemoveAllCommand = ReactiveCommand.Create(() => { 
                RemoveAll();
            });
            SaveProgressCommand = ReactiveCommand.Create((ToDoItemViewModel item) => {
                SaveProgress(item);
            });
            GetAllToDo();
        }
        public ReactiveCommand<Unit, Unit> AddItemCommand { get; }
        public ReactiveCommand<ToDoItemViewModel, Unit> RemoveItemCommand { get; }
        public ReactiveCommand<Unit, Unit> RemoveAllCommand { get; }
        public ReactiveCommand<ToDoItemViewModel, Unit> SaveProgressCommand { get; }
        public ObservableCollection<ToDoItemViewModel> ToDoItems { get; } = new ObservableCollection<ToDoItemViewModel>();

        private string? _newItemContent;
        public string? NewItemContent
        {
            get => _newItemContent;
            set => this.RaiseAndSetIfChanged(ref _newItemContent, value);
        }
        private async void GetAllToDo()
        {
            List<ToDoItem> allToDo = await _toDoItemMethods.GetAllToDo();
            foreach (ToDoItem item in allToDo)
            {
                ToDoItemViewModel toDoItemViewModel = new()
                {
                    IsChecked = item.IsChecked,
                    Content = item.Content,
                    Id = item.Id,
                };
                ToDoItems.Add(toDoItemViewModel);
            }
        }
        private async void AddItem()
        {
            // Add new item to data base
            ToDoItem newItem = new ToDoItem(false, NewItemContent);
            bool success = await _toDoItemMethods.AddToDo(newItem);
            // if sussess get all from database to update UI
            if (success) 
            {
                //clear list first otherwise list will be displayed twice
                ToDoItems.Clear();    
                GetAllToDo();
            }
            // reset the NewItemContent
            NewItemContent = null;
        }

        private async void RemoveItem(ToDoItemViewModel item)
        {
            bool success = await _toDoItemMethods.Delete(item.Id);
            if (success)
            {
                //clear list first otherwise list will be displayed twice
                ToDoItems.Clear();
                GetAllToDo();
            }
        }

        private async void RemoveAll() 
        {
            bool success = await _toDoItemMethods.DeleteAll();
            if (success) 
            {
                ToDoItems.Clear();
            }
        }

        private async void SaveProgress(ToDoItemViewModel item) 
        {
            ToDoItem updateItem = new ToDoItem(item.IsChecked, item.Content, item.Id);
            bool success = await _toDoItemMethods.Update(updateItem);
            if (success) 
            {
                //clear list first otherwise list will be displayed twice
                ToDoItems.Clear();
                GetAllToDo();
            }
        }
    }
}

Ok now the few Questions i have

1. Not sure this follows the correct pattern but it seemed to work best to have ToDoItem.cs as a class that only models the data (just the columns that map to the database) and have the class ToDoItemMethods.cs handle all the CRUD methods. Reason being is I needed a way to pass _unitOfWork to the class that handles CRUD methods but also still needed a convenient way to pass the ToDoItem objects from the ViewModel to the Model for data processing and having UnitOfWork in the ToDoItem class constructor really complicated that. Is this an ok approach or am i missing something obvious?

2. In my GetAllToDo method in the MainWindowViewModel class I needed to map the ToDoItem's that get returned from the database back into ToDoItemViewModel's and add them to the ToDoItems ObservableCollection. I could not find a way to cast a List of ToDoItem's to ObservableCollection of ToDoItemViewModel's. Is there a better way? I guess in general is seems like there is a lot of mapping between ToDoItem objects and the ToDoItemViewModel objects. Guessing that is really the only option?

3. is Singleton correct lifetime for UnitOfWork. I know in web apps we use Scoped but i would assume to use Singleton for desktop? And what lifetime should be used for the AddMySqlDataSource ? (in code above connection Lifetime defaults to Transient and dataSourceLifetime defaults to Singleton) Maybe Singleton for both connection and datasource? Any knowledge here is much appreciated.

It would be great if we could have an official Avalonia MVVM guide on adding in a real database with DI and Repository + UnitOfWork pattern. Seems like a question that gets asked a lot and I haven't found too much information on the best way to do it. If the code i have is written well enough I wouldn't mind sharing the full repo. or maybe even helping write the tutorial if i have time.

Hope this all makes sense and thank you in advanced for taking a look. I know the post is a bit long..

[thevortexcloud]

Is this an ok approach or am i missing something obvious?

If you are interested in maximum correctness, then this is the correct way to do it. Your DTO should be separate from your code that uses it (EG your database logic). That way you can easily create abstractions around it and follow single responsibility principle. This applies to pretty much everything, including ASP Core. That said, I would suggest using a better name than ToDoItemMethods. That said I personally normally structure it a bit differently. EG I will make the following structure

• public interface IDataRepository
• public class SqlLiteDataRepository : IDataRepository

Where the IDataRepository just contains a bunch of methods for CRUD of DTO, and the implementation of it handles all the actual SQL execution and ORM. Then I will inject IDataRepository into my view models/core application logic.

In my GetAllToDo method in the MainWindowViewModel class I needed to map the ToDoItem's that get returned from the database back into ToDoItemViewModel's and add them to the ToDoItems ObservableCollection. I could not find a way to cast a List of ToDoItem's to ObservableCollection of ToDoItemViewModel's. Is there a better way? I guess in general is seems like there is a lot of mapping between ToDoItem objects and the ToDoItemViewModel objects. Guessing that is really the only option?

This is the "correct" pattern as a view model should wrap a model. But since I am lazy I generally just add a constructor to the view model that uses the model as a backing value for the fields/sets the initial values based on it and exposes a method to get the model back out of it.

is Singleton correct lifetime for UnitOfWork. I know in web apps we use Scoped but i would assume to use Singleton for desktop? And what lifetime should be used for the AddMySqlDataSource ? (in code above connection Lifetime defaults to Transient and dataSourceLifetime defaults to Singleton) Maybe Singleton for both connection and datasource? Any knowledge here is much appreciated.

Avalonia wont create scopes for you. You can manually create them yourself though. If it's "correct" or not depends on if the services need to be long lived. Generally for a website you don't want to leave a database connection open as you might get a connection exhaustion/memory leaks. The advantage of scoped services is they also get disposed of when the scope is disposed.

It would be great if we could have an official Avalonia MVVM guide on adding in a real database with DI and Repository + UnitOfWork pattern

As the person who wrote original guide the Avalonia DI guide is based on (and also helped write the Avalonia DI guide), I can say that the guide is just meant to tell you how to bootstrap DI. Not how to actually structure your code. The guide makes a general assumption that you already know how to use DI and just want to set it up.