c# - 无法创建类型为 'MyContext' 的对象。对于设计时支持的不同模式

Question

我在 .NET Core 上有 ConsoleApplication 并且我将我的 DbContext 添加到依赖项，但是我有一个错误:

Unable to create an object of type 'MyContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

我添加了:var context = host.Services.GetRequiredService<MyContext>();我还添加了 private readonly DbContextOptions<MyContext> _opts;在我的帖子类中:

using (MyContext db = new MyContext(_opts))
{
    db.Posts.Add(postData);
    db.SaveChanges();
}

这是我添加服务的方式:

.ConfigureServices((context, services) =>
{
    services.Configure<DataOptions>(opts =>
        context.Configuration.GetSection(nameof(DataOptions)).Bind(opts)
    );
    services.AddDbContext<MyContext>((provider, builder) =>
        builder.UseSqlite(provider.GetRequiredService<IOptions<DataOptions>>().Value.ConnectionString)
    );
});

这是我的上下文:

public sealed class MyContext : DbContext
{
    private readonly DbContextOptions<MyContext> _options;
    
    public DbSet<PostData> Posts { get; set; }
    public DbSet<VoteData> Votes { get; set; }
    
    
    public MyContext(DbContextOptions<MyContext> options) : base(options)
    {
        _options = options;
    }
    
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (!optionsBuilder.IsConfigured)
        {
            optionsBuilder.UseSqlite("ConnectionString");
        }
    }
}

我尝试添加迁移并出现此错误

我做错了什么？

Answer 1

我通过向我的 Context 添加一个简单的构造函数来解决这个问题

public class DataContext : DbContext
{
    public DataContext()
    {
    }

    public DataContext(DbContextOptions options) : base(options)
    {
    }

    protected override void OnConfiguring(DbContextOptionsBuilder options)
    {
        if (!options.IsConfigured)
        {
            options.UseSqlServer("A FALLBACK CONNECTION STRING");
        }
    }
    
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);            
    }
}