如何以及在哪里使用 EF Core 6 为一对多关系设置 FK

Question

我有3张桌子，

Customer

、

Program

和

ProgramRegistrations

。客户是一个 IdentityUser 并在数据库 AspNetUsers 中。我的客户模型有一个

List<ProgramRegistration>

。 ProgramRegistrations 是一个包含 2 列（CustomerId 和 ProgramId）的表，它们构成了该表的复合 PK。

当我尝试保存新的

ProgramRegistration

时，出现以下错误：

The value of 'ProgramRegistrationEntity.CustomerId' is unknown when attempting to save changes. This is because the property is also part of a foreign key for which the principal entity in the relationship is not known.

在 ProgramRegistrationConfiguration 文件中我们创建密钥，

builder.HasKey(x => new {x.CustomerId, x.ProgramId});

在 CustomerConfiguration 文件中我有

builder.HasMany(x => x.ProgramRegistrations).WithOne(y => y.Customer).HasForeignKey(x => x.CustomerId);

我们正在从 EF Core 3 迁移到 EF Core 6，这对我们来说是一个症结所在。我不明白错误消息想告诉我什么。

Answer 1

根据您的描述，您的代码应如下所示

// Customer entity
public class Customer : IdentityUser
{
   // Other properties of Customer
    public List<ProgramRegistration> ProgramRegistrations { get; set; }
}

// Program entity
public class Program
{
   public int ProgramId { get; set; }
   // Other properties of Program
}

// ProgramRegistration entity
public class ProgramRegistration
{
   public int CustomerId { get; set; }
   public int ProgramId { get; set; }
   // Other properties of ProgramRegistration

   public Customer Customer { get; set; }
   public Program Program { get; set; }

}

  // CustomerConfiguration
  public class CustomerConfiguration : IEntityTypeConfiguration<Customer>
  {
     public void Configure(EntityTypeBuilder<Customer> builder)
    {
       builder.HasMany(customer => customer.ProgramRegistrations)
           .WithOne(programRegistration => programRegistration.Customer)
           .HasForeignKey(programRegistration => 
           programRegistration.CustomerId);
    }
}

// ProgramRegistrationConfiguration
public class ProgramRegistrationConfiguration : 
 IEntityTypeConfiguration<ProgramRegistration>
{
   public void Configure(EntityTypeBuilder<ProgramRegistration> builder)
   {
       builder.HasKey(programRegistration => new { 
        programRegistration.CustomerId, programRegistration.ProgramId });
   }
}

并将以上配置注册到您的数据库上下文 onmodelcreating 事件

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
   base.OnModelCreating(modelBuilder);

   // Register configurations
   modelBuilder.ApplyConfiguration(new CustomerConfiguration());
   modelBuilder.ApplyConfiguration(new 
      ProgramRegistrationConfiguration());
    // Other configurations
}