当 Principle 实体中的两个属性指向依赖实体中的同一属性时，如何使用 EF Core？

Question

我有 2 个模型类：

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Department.cs

public class Department
{
    public string DepartmentId { get; set; }

    public string Name { get; set; }

    public string Description { get; set; }

    [ForeignKey("FacultyId")]
    public IList<Faculty> Faculties{ get; set; }

    [ForeignKey("FacultyId")]
    public Faculty HOD { get; set; }

}

---

Faculty.cs

public class Faculty
{
    public string FacultyId { get; set; }

    public string FacultyName { get; set; }

    public FacultyStatus FacultyStatus { get; set; }

    public Designation Designation { get; set; }

    [DataType(DataType.EmailAddress)]
    public string Email { get; set; }

    [DataType(DataType.PhoneNumber)]
    public string PhoneNumber { get; set; }

    public string Address { get; set; }

    public int Experience { get; set; }

    public string Qualifications { get; set; }

    public string Description { get; set; }

    public Department Department{ get; set; }

}

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我无法确定如何为部门设置 HOD。我想到的是，将 HOD 列作为外键，但我不知道这会有多好或有用。 我参考了这个链接来学习，但我无法应用相同的链接

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错误：

无法确定类型为“ICollection<Faculty>”的导航“Department.Faculties”所表示的关系。手动配置关系，或使用“[NotMapped]”属性或使用“OnModelCreating”中的“EntityTypeBuilder.Ignore”忽略此属性。

Note：此问题总结整理于: How to use EF Core when two properties in the Principle entity point to the same attribute in the dependent entity?

Answer 1

在代码中，您希望配置具有多个关系的两个实体（部门和学院）：一对一和一对多。如果是这种情况，您可以考虑使用该属性。InverseProperty

例如：

public class Department  
{  
    public string DepartmentId { get; set; }  
    public string Name { get; set; }  
    public string Description { get; set; }  

    [InverseProperty("FacultyDepartment")]  
    public IList<Faculty> Faculties { get; set; } //navigation property, One-to-Many relationship  

    [InverseProperty("HODDepartment")]  
    public Faculty HOD { get; set; }        //navigation property, One-to-One relationship  
}  
public class Faculty  
{  
    [ForeignKey("HODDepartment")]  
    public string FacultyId { get; set; }   // this property is the primary key, and the one-to-one relationship foreign key. You can also add a new Primary key.  

    public string FacultyName { get; set; }  
       
       
    [DataType(DataType.EmailAddress)]  
    public string Email { get; set; }  
    [DataType(DataType.PhoneNumber)]  
    public string PhoneNumber { get; set; }  
    public string Address { get; set; }  

    public int Experience { get; set; }  

    public string Qualifications { get; set; }  

    public string Description { get; set; }  

    public Department HODDepartment { get; set; }  // one-to-one relationship, navigation property.  

    [ForeignKey("FacultyDepartment")]  
    public string FacultyDepartmentId { get; set; }  //one-to-many relationship foreign key.  
    public Department FacultyDepartment { get; set; } //one to-many relationship , navigation property.  
}  

然后，迁移后，结果如下：

更新：

HOD（这应该是作为 HOD 的学院的 ID）

若要在 DepartMent 表中添加 HodId，可以基于前面的示例代码，在 Departments 类中添加外键：

public class Department  
{  
    public string DepartmentId { get; set; }  
    public string Name { get; set; }  
    public string Description { get; set; }  
    [InverseProperty("FacultyDepartment")]  
    public IList<Faculty> Faculties { get; set; }  
  
    [ForeignKey("HOD")]  
    public string HODId { get; set; }  
    public Faculty HOD { get; set; }  
}  

学院班级如下：

public class Faculty  
{  
    [ForeignKey("HODDepartment")]  
    public string FacultyId { get; set; }  

    public string FacultyName { get; set; }  
       
       
    [DataType(DataType.EmailAddress)]  
    public string Email { get; set; }  
    [DataType(DataType.PhoneNumber)]  
    public string PhoneNumber { get; set; }  
    public string Address { get; set; }  

    public int Experience { get; set; }  

    public string Qualifications { get; set; }  

    public string Description { get; set; }  
    public Department HODDepartment { get; set; }  

    [ForeignKey("FacultyDepartment")]  
    public string FacultyDepartmentId { get; set; }  
    public Department FacultyDepartment { get; set; }  
}  

然后，迁移后，下表如下：

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