entity-framework - 如何首先在 Entity Framework 4 代码中映射复合主键？

Question

我首先要掌握 EF4 代码，并且到目前为止我很喜欢它。但是我无法将实体映射到具有复合主键的表。

我尝试过的配置如下所示：

public SubscriptionUserConfiguration()

    {
                Property(u => u.SubscriptionID).IsIdentity();
                Property(u => u.UserName).IsIdentity();
    }

引发此异常：无法推断实体类型“订阅用户”的键。

我错过了什么？

Answer 1

你也可以使用

HasKey(u => new { u.SubscriptionID, u.UserName });

编辑：

我发现的一个限制是以下不起作用：

public ProjectAssignmentConfiguration()
{
    HasKey(u => u.Employee.EmployeeId);
    HasKey(u => u.Project.ProjectId);
}

或者

public ProjectAssignmentConfiguration()
{
    HasKey(u => new { u.Employee.EmployeeId, u.Project.ProjectId });
}

那么如何设置连接表具有由外键组成的主键的实体呢？

Answer 2

我将尝试使用以下实体逐步解释它

public class Account
{
    public int AccountId1 { get; set; }
    public int AccountId2 { get; set; }
    public string Description { get; set; }
}

1. 创建从EntityTypeConfiguaration<TEntity>Object 派生的类以覆盖约定

   class AccountEntityTypeConfiguration : EntityTypeConfiguration<Account>
   {
   
       public AccountEntityTypeConfiguration()
       {
         // The Key
         // The description of the HasKey Method says
         // A lambda expression representing the property to be used as the primary key.
         // If the primary key is made up of multiple properties then specify an anonymous type including the properties.
         // Example C#: k => new { k.Id1, k.Id2 }
         // Example VB: Function(k) New From { k.Id1, k.Id2 }
         this.HasKey(k => new { k.AccountId1, k.AccountId2 } );  // The Key
   
         // Maybe the key properties are not sequenced and you want to override the conventions
         this.Property(p => p.AccountId1).HasDatabaseGeneratedOption(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.None);
         this.Property(p => p.AccountId2).HasDatabaseGeneratedOption(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.None);
   
         this.Property(p => p.Description).IsRequired();  // This property will be required
         this.ToTable("Account");  // Map the entity to the table Account on the database
       }
   }
   

2. 创建从DbContextObject 派生的类时，覆盖OnModelCreatingMethod 并将新AccountEntityTypeConfiguration对象添加到模型构建器的 Configurations。

   public class MyModelAccount : DbContext
   {
       public DbSet<Account> Accounts { get; set;}
   
       protected override void OnModelCreating(DbModelBuilder modelBuilder)
       {
           // Add a new AccountEntityTypeConfiguration object to the configuration of the model, that will be applied once the model is created. 
           modelBuilder.Configurations.Add(new AccountEntityTypeConfiguration());
       }
   
   }
   

希望对你有帮助！

Answer 3

你也可以使用Column属性

public class UserProfileRole
{
    [Key, Column(Order = 0)]
    public int UserId { get; set; }

    [Key, Column(Order = 1)]
    public int RoleId { get; set; }
}

Answer 4

解决了：我应该使用 HasKey，而不是 Identity。这有效：

public SubscriptionUserConfiguration()
{
     HasKey(u => u.SubscriptionID);
     HasKey(u => u.UserName);
}