实体框架：复合键的字段不能为空？ [英] Entity Framework: field of composite key cannot be nullable?

问题描述

  public class Item 
 {
 [Key，Column（Order = 0）] 
 public int UserId {get;组; } 
 [Key，Column（Order = 1）] 
 public DateTime？日期{get;组; 
} 
  

运行下面的代码会抛出异常 DbEntityValidationException 与消息：日期字段是必需的。：

  var it = new Item {Date = null，UserId = 2}; 
 m_Entities.Items.Add（it）; 
 m_Entities.SaveChanges（）; // throws exception 
  

（ m_Entities DbContext 后代，项目定义为 DbSet< Item> ）
为什么如果可以 null （声明为 DateTime？），则需要日期而如何允许 null 成为 Date 的有效值？

解决方案

从拉斐尔的回答引导我进行另一个搜索。以下是为什么不可能（Cobsy的答案）：

复合主键中的可空列有什么问题？

简而言之：
NULL == NULL - > false

Wierd。我的解决方案是将Id列添加到Model中。

BTW：MySQL允许我不定义主键，那么我被允许有这样的模式 - EF投诉关于不定义密钥： - （。

I have a model with composite key - the row is the key:

public class Item
{
    [Key, Column(Order = 0)]
    public int UserId { get; set; }
    [Key, Column(Order = 1)]
    public DateTime? Date { get; set; }
}

Running the code below it throws an exception DbEntityValidationException with message: The Date field is required.:

var it = new Item { Date = null, UserId = 2 };
m_Entities.Items.Add(it);
m_Entities.SaveChanges(); // throws exception

(m_Entities is usual DbContext descendant with Items defined as DbSet<Item>) Why is the Date required if it can be null (declared as DateTime?) ? And how to allow null to be a valid value for Date?

解决方案

Answer from Raphael lead me to another search. Here is the why it is not possible (answer from Cobsy):

What's wrong with nullable columns in composite primary keys?

In short: NULL == NULL -> false

Wierd. The solution for me is to add Id column into Model.

BTW: MySQL allow me not to define Primary Key, then I'm allowed to have such schema - EF complains about not defining the key :-(.

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