c# - 通过代码零或一关系映射

Question

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头像(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);
    }
}

但是，当尝试运行我的应用程序时，我得到一个 NHibernate.MappingException:

NHibernate.MappingException : Could not compile the mapping document: mapping_by_code----> NHibernate.MappingException : Could not determine type for: MyApp.Models.UserAvatar, MyApp, for columns: NHibernate.Mapping.Column(User)

我无法理解这个神秘的错误。

我如何完成一个 User 可以有零个或一个头像的映射？

Answer 1

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; }
}

具有以下映射:

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);
    }
}