在Entity Framework 4.1 Code First中创建双向一对一关系 [英] Creating BiDirectional One - One relationship in Entity Framework 4.1 Code First

问题描述

我想使用EF Code First在两个实体之间创建双向一对一关系.我在以下代码上遇到麻烦.您认为我该怎么办?

I want to created Bi-Directional One-One relationship between two entities using EF Code First. I have trouble with the following code. What do you think I should do?

public class User
{
    public string ID { get; set; }
    public string LastName { get; set; }
    public string Password { get; set; }
    public string FirstName { get; set; }

    public int ProfileID { get; set; }
    public Profile Profile { get; set; }

}
public class Profile
{
    public int UserID { get; set; }
    public User User { get; set; }
    public int ProfileID { get; set; }
    public string ProfileName { get; set; }

    public DateTime CreateDate { get; set; }
    public DateTime LastUpdateDate { get; set; }

}

我要在两个实体中同时具有导航属性和外键.

I want to have both Navigation property and Foreign Key in both the entities.

这给了我错误.我可以使用Fluent Mapping API做些什么?

This gives me error. What can do I in Fluent Mapping API to make this work?

推荐答案

使用此:

public class User
{
    public string ID { get; set; }
    public string LastName { get; set; }
    public string Password { get; set; }
    public string FirstName { get; set; }
    public Profile Profile { get; set; }
}

public class Profile
{
    [Key, ForeignKey("User")]
    public int ProfileID { get; set; }
    public string ProfileName { get; set; }
    public DateTime CreateDate { get; set; }
    public DateTime LastUpdateDate { get; set; }
    public User User { get; set; }
}

这是在EF中建立一对一关系的唯一有效方法-从属实体的PK也必须与主体实体FK相同. EF中没有像双向一对一关系那样的东西，因为它不能在EF中工作.

That is the only valid way to build one-to-one relation in EF - PK of the dependent entity must be also FK to principal entity. There is nothing like bidirectional one-to-one relation in EF because it cannot work in EF.

人们有时如何克服这一问题的方式是两个一对多的关系，其中主体不具有相关实体的导航集合+在数据库中手动定义的唯一键.需要手动映射:

The way how people sometimes overcome this are two one-to-many relations where principal doesn't have navigation collection for dependent entities + manually defined unique keys in the database. That require manual mapping:

public class User
{
    public string ID { get; set; }
    public string LastName { get; set; }
    public string Password { get; set; }
    public string FirstName { get; set; }
    // one side MUST be nullable otherwise you have bidirectional constraint where each
    // entity demands other side to be inserted first = not possible
    public int? ProfileId { get; set; } 
    public Profile Profile { get; set; }
}

public class Profile
{
    public int ProfileID { get; set; }
    public string ProfileName { get; set; }
    public DateTime CreateDate { get; set; }
    public DateTime LastUpdateDate { get; set; }
    public int UserId { get; set; }
    public User User { get; set; }
}

在映射中，您将定义:

modelBuilder.Entity<User>
            .HasOptional(u => u.Profile)
            .WithMany()
            .HasForeignKey(u => u.ProfileId);
modelBuilder.Entity<Profile>
            .HasRequired(u => u.User)
            .WithMany()
            .HasForeignKey(u => u.UserId);

现在，您必须在数据库中定义唯一键-如果您首先使用代码，请使用

Now you must define Unique keys in the database - if you are using code first use custom database initializer. Be aware that still bidirectional one-to-one is wrong concept because both sides demand unique FK where NULL is still included in unique values so once you insert User before Profile there mustn't be any other User without Profile. That probably leads to serializable transaction.

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