EF4.1异常创建具有每层次表继承的数据库 [英] EF4.1 Exception creating Database with table-per-hierarchy inheritance

问题描述

我创建了一个非常简单的项目来演示每个层次结构表的不一致性。在我试图生成数据库的单元测试中，我根据配置得到了一些错误：

I have created a very simple project to demonstrate table-per-hierarchy inhertiance. In my unit test which tries to generate the database, i get one of a number of errors depending on the config:

没有必需（） method

Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false));
Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true));

交付：

System.Data.DataException : An exception occurred while initializing the database. See the InnerException for details.
  ----> System.Data.EntityCommandCompilationException : An error occurred while preparing the command definition. See the inner exception for details.
  ----> System.Data.MappingException : 
(6,10) : error 3032: Problem in mapping fragments starting at line 6:Condition member 'User.IsActive' with a condition other than 'IsNull=False' is mapped. Either remove the condition on User.IsActive or remove it from the mapping.

使用必需（）方法：

Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false).IsRequired());

Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true).IsRequired());

交付：

System.Data.DataException : An exception occurred while initializing the database. See the InnerException for details.
  ----> System.Data.EntityCommandCompilationException : An error occurred while preparing the command definition. See the inner exception for details.
  ----> System.Data.MappingException : 
(6,10) : error 3023: Problem in mapping fragments starting at lines 6, 13, 19:Column User.IsActive has no default value and is not nullable. A column value is required to store entity data.

根据我的理解，我们不应该在基类型上定义鉴别器列/属性，但无论哪种方式无论是否定义了列，它似乎没有区别：

From what I understand we should not define the discriminator column/property on the base type, but either way it seems to make no difference with or without the column defined:

  public class User
  {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public virtual int Id { get; set; }

    [Required]
    public virtual string Username { get; set; }

    [Required]
    [DefaultValue(true)]
    public bool IsActive { get; set; } //have tried without this property
  }

  public class InActiveUser : User
  {
    public virtual DateTime DeActivatedDate { get; set; }
  }

  public class ActiveUser : User
  {
  }

推荐答案

您无法将鉴别器映射为实体中的属性。 Discriminator定义实体的类型。原因很清楚 - 鉴别器定义了实例类型。如果您能够在运行时更改鉴别值，会发生什么？ .NET应如何更改实例化对象的类型？

You cannot map discriminator as property in the entity. Discriminator defines type of the entity. The reason is clear - discriminator defines instanced type. What should happen if you would be able to change discriminator value at runtime? How should .NET change the type of instanced object?

将实体定义为：

public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public virtual int Id { get; set; }

    [Required]
    public virtual string Username { get; set; }
}

public class InActiveUser : User
{
    public virtual DateTime DeActivatedDate { get; set; }
}

public class ActiveUser : User
{ }

这应该有效：

modelBuilder.Entity<User>()
            .Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false))
            .Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true));

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