实体框架中的映射

Question

I have an existing DB schema like this (cant change it ..) . I need to do a EF mapping

Student table:

ID    Name     CourseID
------------------------
 1    Name1     100023
 2    Name2     100023
 3    Name3     100024  
 4    Name4     NULL  

Course table:

ID   CourseID   CourseName
--------------------------
 1   100023      Course1  
 2   100022      Course2  
 3   100024      Course3  
 4   100023      Course1  

ID is the primary key in both the tables. CourseID is the column for the relationships.

There is no explicit relationship in the database (SQL Server) also.

When I try to do a mapping in EF by specifying CourseID as the key required to do the mapping it throws up an error telling it is not defined as the key property. I cannot add it as the Key property as it is a null-able field.

Is there any way I could do this mapping?

Answer 1

That's a pretty rough schema to work with. However, you might be able to use a composite key for the courses table. I haven't tested it, but something like this should work.

public class Course
{
    [Key, Column(Order = 0)]
    public int ID { get; set; }

    [Key, Column(Order = 1)]
    public int? CourseID { get; set; }

    public string CourseName { get; set; }
}

public class Student
{
    [Key]
    public int ID { get; set; }

    public string Name { get; set; }

    public int? CourseID { get; set; }

    [ForeignKey("CourseID")]
    public Course Course { get; set; }
}