WPF.Net6專案（EF、MVVM）中的DbContextFactory

當我使用普通/經典DBContext實作時，我的應用程式運行良好，但是當我嘗試時DbContextFactory，_contextFactory.CreateDbContext()總是因“null”例外而失敗。我錯過了什么？

我的App.xaml.cs（使用時無需更改此檔案DBContext）：

private void ConfigureServices(IServiceCollection services)
{
    string defaultConnection = Settings.Default.DefaultConnection;

    services.AddDbContextFactory<MyDbContext>(options => options.UseMySql(defaultConnection, ServerVersion.AutoDetect(defaultConnection)));

    services.AddTransient(typeof(MainWindow));
}

MyDbContext.cs檔案（不需要更改，因為它似乎DbContextFactory已經符合建構式的要求）：

public class MyDbContext : DbContext
{
    public MyDbContext (DbContextOptions<MyDbContext> options)
        : base(options)
    {
    }
    
    // DbSets 

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (!optionsBuilder.IsConfigured)
        {
            string defaultConnection = Settings.Default.DefaultConnection;

            var options = new DbContextOptionsBuilder<MyDbContext>()
                            .UseMySql(defaultConnection, ServerVersion.AutoDetect(defaultConnection))
                            .Options;
        }

        optionsBuilder.UseLazyLoadingProxies();
        // To be disabled in production 
        optionsBuilder.LogTo(Console.WriteLine, LogLevel.Information);
        optionsBuilder.EnableSensitiveDataLogging();
        optionsBuilder.EnableDetailedErrors();
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Table building logic for EF code-first
    }
}

MainWindow.xaml.cs檔案：

public partial class MainWindow : Window
{
    private readonly IDbContextFactory<MyDbContext> _contextFactory;

    private SomeVieModel _someVieModel;

    public MainWindow()
    {
        InitializeComponent();

        var _context = _contextFactory.CreateDbContext(); // Throws 'null' exception

        // Probably should be instantiating a new DbContext 
        // in the VM itself, instead of passing it on? 
        _someVieModel = new SomeVieModel(_context); 
    }
}

我檢查了許多 Blazor 示例，因為缺少 WPF 示例，我覺得我錯過了一些非常簡單的東西，一些DbContextFactory物件實體化的行？就像在這個例子中一樣-IDbContextFactory<MyDbContext> contextFactory物件來自哪里以及它在哪里實體化？謝謝！

uj5u.com熱心網友回復：

我想我已經解決了，盡管我相信你們中的一些人會指出我的方式的錯誤:)

我剛剛意識到，我已經DbContextFactory為資料庫遷移創建了自己的類，否則 EF Core 無法DbContext單獨通過專案的類連接到資料庫。

public class MyDbContextFactory : IDesignTimeDbContextFactory<MyDbContext>
{
    public MyDbContext CreateDbContext(string[]? args = null)
    {
        string defaultConnection = Settings.Default.DefaultConnection;

        var optionsBuilder = new DbContextOptionsBuilder<MyDbContext>();
        optionsBuilder.UseMySql(defaultConnection, ServerVersion.AutoDetect(defaultConnection));

        return new MyDbContext(optionsBuilder.Options);
    }
}

我已經注釋掉了代碼并通過我自己的類而不是介面進行App.xaml.cs了初始化：DbContextFactoryIDbContextFactory

public partial class MainWindow : Window
{
    private readonly MyDbContextFactory  _contextFactory;

    private SomeVieModel _someVieModel;

    public MainWindow()
    {
        InitializeComponent();

        _contextFactory = new MyDbContextFactory();

        _someVieModel = new SomeVieModel(_contextFactory); 
    }
}

CreateDbContext()并在視圖模型中呼叫：

public class SomeVieModel : ViewModelBase
{
    private readonly MyDbContextFactory _contextFactory;

    public SomeVieModel(MyDbContextFactory contextFactory)
    {
        _contextFactory = contextFactory; 
        
        await LoadDBStuff();
    }
    
    private async Task LoadDBStuff()
    {
        using (var context = _contextFactory.CreateDbContext())
        {
            await context.SomeDataModel.LoadAsync();
            SomeDataModelObservableCollection = context.SomeDataModel.Local.ToObservableCollection();
        }
    }
}

標籤：C＃wpf实体框架.net-core虚拟机

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