WPFでデータベースを更新するサンプルアプリ【CRUD,MVVM】

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net8.0-windows</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <UseWPF>true</UseWPF>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="LiteDB" Version="5.0.21" />
  </ItemGroup>

</Project>

using LiteDB;
using System.Collections.ObjectModel;

using Helpers;

namespace CrudSample;

public class MainViewModel : Helpers.ViewModelBase
{
    private const string DbPath = "sample.db";

    public ObservableCollection<Person> Items { get; } = new();

    private Person? _selectedItem;
    public Person? SelectedItem
    {
        get => _selectedItem;
        set
        {
            _selectedItem = value;
            OnPropertyChanged();

            if (value != null)
            {
                Name = value.Name;
                Age = value.Age;
                IsNewMode = false; // 編集モード
            }
            else
            {
                UpdateFields();
            }

            DeleteCommand.RaiseCanExecuteChanged();
            UpdateCommand.RaiseCanExecuteChanged();
        }
    }
    private void UpdateFields()
    {
        UpdateCommand.RaiseCanExecuteChanged();
        DeleteCommand.RaiseCanExecuteChanged();
    }

    private string _name = "";
    public string Name
    {
        get => _name;
        set
        {
            if (_name == value) return;
            _name = value;
            OnPropertyChanged();

            // ★ 追加の条件が Name に依存するので再評価
            AddCommand.RaiseCanExecuteChanged();
        }
    }

    private int _age;
    public int Age
    {
        get => _age;
        set
        {
            if (_age == value) return;
            _age = value;
            OnPropertyChanged();
        }
    }

    private bool _isNewMode;
    public bool IsNewMode
    {
        get => _isNewMode;
        set
        {
            _isNewMode = value;
            OnPropertyChanged();

            NewCommand.RaiseCanExecuteChanged();
            AddCommand.RaiseCanExecuteChanged();
            UpdateCommand.RaiseCanExecuteChanged();
            DeleteCommand.RaiseCanExecuteChanged();
        }
    }
    public RelayCommand NewCommand { get; }
    public RelayCommand AddCommand { get; }
    public RelayCommand UpdateCommand { get; }
    public RelayCommand DeleteCommand { get; }

    public MainViewModel()
    {
        NewCommand = new RelayCommand(
            () =>
            {
                SelectedItem = null;
                Name = "";
                Age = 0;
                IsNewMode = true;
            },
            () => !IsNewMode
        );
        AddCommand = new RelayCommand(
            Add,
            () => IsNewMode && !string.IsNullOrWhiteSpace(Name)
        );

        UpdateCommand = new RelayCommand(
            Update,
            () => !IsNewMode && SelectedItem != null
        );

        DeleteCommand = new RelayCommand(
            Delete,
            () => !IsNewMode && SelectedItem != null
        );

        Load();

        IsNewMode = true;
    }

    private void Load()
    {
        Items.Clear();
        using var db = new LiteDatabase(DbPath);
        var col = db.GetCollection<Person>("persons");

        foreach (var p in col.FindAll())
            Items.Add(p);
    }

    private void Add()
    {
        var p = new Person { Name = Name, Age = Age };

        using var db = new LiteDatabase(DbPath);
        db.GetCollection<Person>("persons").Insert(p);

        Items.Add(p);
        SelectedItem = p;
    }

    private void Update()
    {
        if (SelectedItem == null) return;

        SelectedItem.Name = Name;
        SelectedItem.Age = Age;

        using var db = new LiteDatabase(DbPath);
        db.GetCollection<Person>("persons").Update(SelectedItem);

        OnPropertyChanged(nameof(Items));
    }

    private void Delete()
    {
        if (SelectedItem == null) return;

        using var db = new LiteDatabase(DbPath);
        db.GetCollection<Person>("persons").Delete(SelectedItem.Id);

        Items.Remove(SelectedItem);
        SelectedItem = null;
        Name = "";
        Age = 0;
    }
}

using System.Windows;

namespace CrudSample;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
}

using LiteDB;

public class Person
{
    [BsonId]
    public int Id { get; set; }

    public string Name { get; set; } = "";
    public int Age { get; set; }
}

using System.Windows.Input;

namespace Helpers;
public class RelayCommand : ICommand
{
    private readonly Action _execute;
    private readonly Func<bool>? _canExecute;

    public RelayCommand(Action execute, Func<bool>? canExecute = null)
    {
        _execute = execute;
        _canExecute = canExecute;
    }

    public bool CanExecute(object? parameter) => _canExecute?.Invoke() ?? true;

    public void Execute(object? parameter) => _execute();

    public event EventHandler? CanExecuteChanged;
    public void RaiseCanExecuteChanged()
        => CanExecuteChanged?.Invoke(this, EventArgs.Empty);
}

using System.ComponentModel;
using System.Runtime.CompilerServices;

namespace Helpers;

public abstract class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler? PropertyChanged;

    protected void OnPropertyChanged([CallerMemberName] string? name = null)
        => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}

<Application x:Class="CrudSample.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:CrudSample"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
         
    </Application.Resources>
</Application>

<Window x:Class="CrudSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:CrudSample"
        mc:Ignorable="d"
        FontSize="20"
        Title="LiteDB CRUD (ComboBox)" Width="400" Height="250">

    <Window.DataContext>
        <local:MainViewModel />
    </Window.DataContext>

    <StackPanel Margin="10" VerticalAlignment="Top">

        <ComboBox ItemsSource="{Binding Items}"
                  SelectedItem="{Binding SelectedItem}"
                  DisplayMemberPath="Name"
                  Margin="0,0,0,10"/>

        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Name" Width="64"/>
            <TextBox
                Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}"
                Width="200"/>
        </StackPanel>

        <StackPanel Orientation="Horizontal" Margin="0,5,0,10">
            <TextBlock Text="Age" Width="64"/>
            <TextBox Text="{Binding Age}" Width="200"/>
        </StackPanel>

        <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
            <Button Content="新規"
                    Width="70" Margin="5"
                    Command="{Binding NewCommand}"/>

            <Button Content="追加"
                    Width="70" Margin="5"
                    Command="{Binding AddCommand}"/>

            <Button Content="更新"
                    Width="70" Margin="5"
                    Command="{Binding UpdateCommand}"/>

            <Button Content="削除"
                    Width="70" Margin="5"
                    Command="{Binding DeleteCommand}"/>
        </StackPanel>

    </StackPanel>
</Window>