具有其他属性的关系映射表? [英] Relationship mapping table with additional properties?

问题描述

我有三节课:

public partial class Student : Contact
{   
    //Inherited from Contact:
    //public int ContactId { get; set; }
    //public string FirstName { get; set; }
    //public string LastName { get; set; }

    public virtual StudentExam StudentExam { get; set; }
}

public partial class Exam
{
    public int ExamId { get; set; }
    public string Title { get; set; }
    public DateTime Date { get; set; }

    public virtual StudentExam StudentExam { get; set; }
}

public partial class StudentExam
{
    public byte Score { get; set; }
    public int ContactId { get; set; }
    public int ExamId { get; set; }

    public virtual Student Student { get; set; }
    public virtual Exam Exam { get; set; }
}

当尝试初始化DbContext时，它抛出ModelValidationException: 在模型生成过程中检测到一个或多个验证错误: \ tSystem.Data.Entity.Edm.EdmEntityType::EntityType'StudentExam'没有定义键.定义此EntityType的键. \ tSystem.Data.Entity.Edm.EdmEntitySet:EntityType:EntitySet'StudentExams'基于未定义键的'StudentExam'类型.

When trying to initialize the DbContext, it throws a ModelValidationException: One or more validation errors were detected during model generation: \tSystem.Data.Entity.Edm.EdmEntityType: : EntityType 'StudentExam' has no key defined. Define the key for this EntityType. \tSystem.Data.Entity.Edm.EdmEntitySet: EntityType: EntitySet 'StudentExams' is based on type 'StudentExam' that has no keys defined.

我尝试将StudentExam类的属性更改为以下内容:

I tried changing the StudentExam class' properties to the following:

[Key, ForeignKey("Student"), Column(Order = 0)]
public int ContactId { get; set; }
[Key, ForeignKey("Exam"), Column(Order = 1)]
public int ExamId { get; set; }

现在我得到此异常:

\ tSystem.Data.Entity.Edm.EdmAssociationEnd::多重性在关系'StudentExam_Student'中的角色'StudentExam_Student_Source'中无效.因为从属角色属性不是关键属性，所以从属角色多重性的上限必须为'*'. \ tSystem.Data.Entity.Edm.EdmAssociationEnd::多重性在关系'StudentExam_Exam'中的角色'StudentExam_Exam_Source'中无效.由于从属角色属性不是关键属性，因此从属角色多重性的上限必须为'*'.

\tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'StudentExam_Student_Source' in relationship 'StudentExam_Student'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'. \tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'StudentExam_Exam_Source' in relationship 'StudentExam_Exam'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

有什么方法可以通过数据注释来实现这一点(我不喜欢在可以使用数据注释时使用流利的API；流利的API会导致代码混乱.

Is there any way to achieve this in with data annotations (I don't like using the fluent API when I can use data annotations; The fluent API leads to messy code.

推荐答案

这与数据注释或流畅的api无关，而是与定义不正确的类有关-您的类中定义的关系根本无法映射，因为它们在关系级别上无效.您必须修改您的课程:

It is not about data annotations or fluent api but about incorrectly defined classes - relations defined in your classes cannot be mapped at all because they are not valid at relational level. You must modify your classes:

public partial class Student : Contact
{   
    public virtual ICollection<StudentExam> StudentExams { get; set; }
}

public partial class Exam
{
    ...

    public virtual ICollection<StudentExam> StudentExams { get; set; }
}

一旦定义了这种关系，就可以使用数据注释在StudentExam类中定义键，它将起作用.

Once you have this relations defined you can use your data annotations for defining keys in StudentExam class and it will work.

顺便说一句.流利的api不会导致凌乱的代码.混乱的代码是由程序员而不是由API创建的.数据注释又违反了POCO原则.

Btw. fluent api doesn't lead to messy code. Messy code is created by programmer, not by API. Data annotations in turn violates POCO principle.

这篇关于具有其他属性的关系映射表?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！