我有以下数据库结构,我无法更改:
CREATE TABLE Users (
ID INT NOT NULL IDENTITY(1,1),
PRIMARY KEY(ID)
)
CREATE TABLE UserAvatars (
UserID INT NOT NULL,
Width INT NOT NULL,
Height INT NOT NULL,
PRIMARY KEY(UserID),
FOREIGN KEY(UserID) REFERENCES Users(ID),
)
基本上,用户可以拥有零个或一个化身(我删除了列以简化示例)。
class User
{
public int ID { get; protected set; }
public UserAvatar Avatar { get; set; }
}
class UserAvatar
{
public User User { get; set; }
public int Width { get; set; }
public int Height { get; set; }
}
我正在使用以下映射:
class UserMapping : ClassMapping<User>
{
public UserMapping()
{
Id(x => x.ID, m => {
m.Generator(Generators.Identity);
});
OneToOne(x => x.Avatar);
}
}
class UserAvatarMapping : ClassMapping<UserAvatar>
{
public UserAvatar()
{
Id(x => x.User, m =>
{
m.Generator(Generators.Foreign<User>(u => u.ID));
});
Property(x => x.Width);
Property(x => x.Height);
}
}
然而,当我尝试运行我的应用程序时,我得到了NHibernate.MappingException
:
NHibernate.MappingException:无法编译映射文档:mapping_by_code---->NHibernate.MappingException:无法确定为以下列键入:MyApp.Models.UserAvatar,MyApp:NHibernate.映射.列(用户)
我无法理解这个神秘的错误。
如何完成User
可能有零个或一个化身的映射?
根据Radim Köhler的指导,解决问题的最终类/映射:
class User
{
public int ID { get; protected set; }
public UserAvatar Avatar { get; set; }
}
class UserAvatar
{
public int UserID { get; protected set; }
public User User { get; set; }
public int Width { get; set; }
public int Height { get; set; }
}
使用以下映射:
class UserMapping : ClassMapping<User>
{
public UserMapping()
{
Id(x => x.ID, m => {
m.Generator(Generators.Identity);
});
OneToOne(x => x.Avatar, m =>
{
m.Cascade(Cascade.All);
m.Constrained(false);
});
}
}
class UserAvatarMapping : ClassMapping<UserAvatar>
{
public UserAvatar()
{
Id(x => x.UserID, m =>
{
m.Generator(Generators.Foreign<UserAvatar>(u => u.User));
});
OneToOne(x => x.User, m =>
{
m.Constrained(true);
});
Property(x => x.Width);
Property(x => x.Height);
}
}
ID几乎对NHibernate(ORM)映射的每个实体都很重要。因此,我们应该扩展Avatar类:
class UserAvatar
{
// every(stuff) should have its ID
public int ID { get; protected set; }
public User User { get; set; }
...
ID值将通过一对一关系进行管理。所以,现在让我们调整映射。
public UserAvatar()
{
Id(x => x.ID);
HasOne(x => x.User)
.Constrained()
.ForeignKey();
...
public UserMapping()
{
Id(x => x.ID);
HasOne(s => s.Avatar).Cascade.All();
相关且非常有趣的阅读:
- 如何进行流畅的nhibernate一对一映射
- Fluent NHibernate&HasOne():如何实现一对一关系