非空属性引用null或瞬时值 - 逆的理解和级联

Question

This是我的数据库项目的片段，并this是产生DB汽车的片段，该功能NHibernate

这些都是我的实体和映射类在上面的DB项目的Fluent NHibernate中。

实体：

public class BaseEntity<T> where T : BaseEntity<T> { 
    public virtual int Id { get; set; } 
... 
} 

public class Person<T> : BaseEntity<T> where T : BaseEntity<T> { 
    public virtual string FirstName { get; set; } 
    public virtual string SecondName { get; set; } 
    public virtual string LastName { get; set; } 
    public virtual string PESEL { get; set; } 
    public virtual DateTime BirthDate { get; set; } 
    public virtual string City { get; set; } 
    public virtual string PostalCode { get; set; } 
    public virtual string Street { get; set; } 
    public virtual string HouseNr { get; set; } 
    public virtual string ApartmentNr { get; set; } 
    public virtual string PhoneNr { get; set; } 
    public virtual string Email { get; set; } 
} 

public class DrivingLicense : BaseEntity<DrivingLicense> { 
    #region Relations 
    public virtual IList<DrivingLicensePermissions> DrivingLicensePermissions { get; set; } 
    public virtual Student Student { get; set; } 
    #endregion 

    public virtual DateTime IssueDate { get; set; } 
    public virtual string DrivingLicenseNr { get; set; } 
} 

public class DrivingLicensePermissions : BaseEntity<DrivingLicensePermissions> { 
    #region Relations 
    public virtual DrivingLicense DrivingLicense { get; set; } 
    #endregion 

    public virtual DrivingLicenseCategory Category { get; set; } 
} 

映射：

class StudentMap : ClassMap<Student> { 
    public StudentMap() { 
     Id(x => x.Id); 
     Map(x => x.FirstName).Not.Nullable().Length(25); 
     Map(x => x.SecondName).Nullable().Length(25); 
     Map(x => x.LastName).Not.Nullable().Length(50); 
     Map(x => x.PESEL).Nullable().Length(11); 
     Map(x => x.BirthDate).Not.Nullable(); 
     Map(x => x.City).Not.Nullable().Length(50); 
     Map(x => x.PostalCode).Nullable().Length(6); 
     Map(x => x.Street).Not.Nullable().Length(50); 
     Map(x => x.HouseNr).Not.Nullable().Length(10); 
     Map(x => x.ApartmentNr).Nullable().Length(10); 
     Map(x => x.PhoneNr).Nullable().Length(20); 
     Map(x => x.Email).Nullable().Length(100); 

     References(x => x.DrivingLicense).Nullable().Cascade.All(); 
     References(x => x.User).Nullable().Cascade.All(); 
     HasMany(x => x.Participants).Cascade.All(); 
    } 
} 

class DrivingLicenseMap : ClassMap<DrivingLicense> { 
    public DrivingLicenseMap() { 
     Id(x => x.Id); 
     Map(x => x.IssueDate).Not.Nullable(); 
     Map(x => x.DrivingLicenseNr).Not.Nullable().Length(20); 

     HasMany(x => x.DrivingLicensePermissions).Cascade.All(); 
     References(x => x.Student).Not.Nullable(); 
    } 
} 

class DrivingLicensePermissionsMap : ClassMap<DrivingLicensePermissions> { 
    public DrivingLicensePermissionsMap() { 
     Id(x => x.Id); 
     Map(x => x.Category).Not.Nullable(); 

     References(x => x.DrivingLicense).Not.Nullable(); 
    } 
} 

而我的问题是这样的例外：非空属性引用null或瞬时值Model.Entities.DrivingLicense 。学生，而我试图坚持学生对象这样

session.Save(student); 

已分配DrivingLicense对象将其

的DrivingLicense财产。

我认为这是由于错误的映射 - 错误的级联或缺少反向引起的。我尝试了许多组合，但无法完成工作。 也是正确的，学生表有DrivingLicense_id和相反，DrivingLicense有Student_id列？！

Answer 1

为了解决我的问题，我不得不将Reference-to-Reference改为HasOne-to-Reference。

现在看起来像这样。

实体没有改变

映射：

class StudentMap : ClassMap<Student> { 
    public StudentMap() { 
     Id(x => x.Id); 
     Map(x => x.FirstName).Not.Nullable().Length(25); 
     Map(x => x.SecondName).Nullable().Length(25); 
     Map(x => x.LastName).Not.Nullable().Length(50); 
     Map(x => x.PESEL).Nullable().Length(11); 
     Map(x => x.BirthDate).Not.Nullable(); 
     Map(x => x.City).Not.Nullable().Length(50); 
     Map(x => x.PostalCode).Nullable().Length(6); 
     Map(x => x.Street).Not.Nullable().Length(50); 
     Map(x => x.HouseNr).Not.Nullable().Length(10); 
     Map(x => x.ApartmentNr).Nullable().Length(10); 
     Map(x => x.PhoneNr).Nullable().Length(20); 
     Map(x => x.Email).Nullable().Length(100); 

     HasOne(x => x.DrivingLicense).PropertyRef(x => x.Student).Cascade.All(); 
     References(x => x.User).Unique().Not.Nullable(); 
     HasMany(x => x.Participants).Cascade.All(); 
    } 
} 

class DrivingLicenseMap : ClassMap<DrivingLicense> { 
    public DrivingLicenseMap() { 
     Id(x => x.Id); 
     Map(x => x.IssueDate).Not.Nullable(); 
     Map(x => x.DrivingLicenseNr).Not.Nullable().Length(20); 

     HasMany(x => x.DrivingLicensePermissions).Cascade.All(); 
     References(x => x.Student).Unique().Not.Nullable(); 
    } 
} 

class DrivingLicensePermissionsMap : ClassMap<DrivingLicensePermissions> { 
    public DrivingLicensePermissionsMap() { 
     Id(x => x.Id); 
     Map(x => x.Category).Not.Nullable(); 

     References(x => x.DrivingLicense).Nullable(); 
    } 
} 

感谢这一变化，循环引用不见了。 see it here

在Students表中没有DrivingLicense_id，现在我可以将Driving实体与DrivingLicense一起保存，并且它的权限只需像以前一样保存学生即可。

session.Save(student); 

Answer 2

此问题的关键是DrivingLicense通过Not.Nullable()映射引用Student。这意味着当NH试图坚持DrivingLicense时，它的Student属性不能是null。

调试代码并在Save(student)调用中暂停。查看对象图，看看student的DrivingLicense属性及其Student属性。我的猜测是它是null。

您需要查看映射的Not.Nullable()方面，或确保您的对象图在持续之前正确“连线”。