EF代码第一 - 1对1可选关系 [英] EF Code First - 1-to-1 Optional Relationship
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问题描述
简单模式:
我想在现有数据库中使用EF Code First映射一个可选的1对1关系。
用户
用户名
联系人
联系
ID
名称
显然,ContactID加入Contact.ID。 ContactID字段为空,所以关系是可选的 - 0或1,从不会很多。
那么如何在EF Code First中用这个现有的模式指定这种关系?
以下是我迄今为止所尝试的:
public class用户
{
[Key]
public string Username {get;组; }
public int? ContactID {get;组; }
[ForeignKey(ContactID)]
public virtual联系Contact {get;组;
}
public class联系
{
[Key]
public int ID {get;组; }
public string Name {get;组; }
public virtual User User {get;组;
}
modelBuilder.Entity< User>()。HasOptional< Contact>(u => u.Contact)
.WithOptionalDependent(c => c.User );
我得到以下异常:
System.Data.Edm.EdmAssociationEnd::在User_Contact关系中的角色
'User_Contact_Source'中,多项式无效。因为Dependent
角色属性不是关键属性,因此从属角色的多重性
的上限必须为*。
解决方案
一个解决方案是;
public class User
{
[Key]
public string Username {get;组; }
public virtual联系Contact {get;组;
}
public class联系
{
[Key]
public int ID {get;组; }
public string Name {get;组; }
public virtual User User {get;组;
}
modelBuilder.Entity< User>()
.HasOptional< Contact>(u => u.Contact)
.WithOptionalDependent(c => ; c.User).Map(p => p.MapKey(ContactID));
您只在POCO中设置导航对象,而是使用流畅的API将您的密钥映射到正确栏。
I want to map an optional 1-to-1 relationship in an existing database with EF Code First.
Simple schema:
User
Username
ContactID
Contact
ID
Name
Obviously ContactID joins to Contact.ID. The ContactID field is nullable so the relationship is optional - 0 or 1, never many.
So how do I specify this relationship in EF Code First, with this existing schema?
Here's what I've tried so far:
public class User
{
[Key]
public string Username { get; set; }
public int? ContactID { get; set; }
[ForeignKey("ContactID")]
public virtual Contact Contact { get; set; }
}
public class Contact
{
[Key]
public int ID { get; set; }
public string Name { get; set; }
public virtual User User { get; set; }
}
modelBuilder.Entity<User>().HasOptional<Contact>(u=> u.Contact)
.WithOptionalDependent(c => c.User);
I get the following Exception:
System.Data.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role
'User_Contact_Source' in relationship 'User_Contact'. Because the Dependent
Role properties are not the key properties, the upper bound of the multiplicity
of the Dependent Role must be *.
解决方案
One solution would be;
public class User
{
[Key]
public string Username { get; set; }
public virtual Contact Contact { get; set; }
}
public class Contact
{
[Key]
public int ID { get; set; }
public string Name { get; set; }
public virtual User User { get; set; }
}
modelBuilder.Entity<User>()
.HasOptional<Contact>(u => u.Contact)
.WithOptionalDependent(c => c.User).Map(p => p.MapKey("ContactID"));
You set only your navigational objects in your POCOs and instead you use fluent API to map your key to the correct column.
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