如果您打算使用无键实体类型，请在“OnModelCreating”中调用“HasNoKey”。NET Keyless 属性错误

Question

我正在使用 C# (.NET) 开发一个项目，我想进行初始迁移，但遇到了问题。我尝试了很多解决方案，但仍然出现错误。

AppDBContext：

 protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            object value = modelBuilder.Entity<Actor_Movie>().HasKey(am => new
            {  
                am.ActorId,
                am.MovieId,
            }
            );

            modelBuilder.Entity<Actor_Movie>().HasOne(m => m.Movie).WithMany(am => am.Actors_Movies).HasForeignKey(m => m.MovieId);

            modelBuilder.Entity<Actor_Movie>().HasOne(m => m.Actor).WithMany(am => am.Actors_Movies).HasForeignKey(m => m.ActorId);

            base.OnModelCreating(modelBuilder);


        }

MovieCategory.cs：

namespace eTickets.Data.Enums;

public class MovieCategory
{

}

错误：

PM> add-migration initial
Build started...
Build succeeded.
System.InvalidOperationException: The entity type 'MovieCategory' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'. For more information on keyless entity types, see https://go.microsoft.com/fwlink/?linkid=2141943.
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.ValidateNonNullPrimaryKeys(IModel model, IDiagnosticsLogger`1 logger)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.Validate(IModel model, IDiagnosticsLogger`1 logger)

 Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
The entity type 'MovieCategory' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'. For more information on keyless entity types, see https://go.microsoft.com/fwlink/?linkid=2141943.

让我知道我做错了什么。

Answer 1

在实体框架中，大多数实体都有一个唯一标识符来引用它们。错误消息表明您的 MovieCategory 类缺少这样的标识符。将Id 属性添加到MovieCategory：

public class MovieCategory
{
  public int Id { get; set; }
}

如果您打算创建无密钥实体，请使用错误消息中描述的方法或使用 Keyless 属性标记类（来自 EF Core 5）：

[Keyless]
public class MovieCategory
{
}

更多关于无钥匙实体的信息可以在here找到。