Question

I’m working with the EF code first approach and want to add a link (map) table. I am working off the below example and get the following error:

System.Data.Entity.Edm.EdmEntityType: : EntityType 'EmployeeDepartmentLink' has no key defined. Define the key for this EntityType.

Problem is I dont want a key on this table it just maps the two tables together:

public class Employee
{
    [Key()]
    public int EmployeeID;
    public string Name;
}

public class Department
{
    [Key()]
    public int DepartmentID;
    public string Name;
}

public class EmployeeDepartmentLink
{
    public int EmployeeID;
    public int DepartmentID;
}

I have tried a variety of things like adding the “[Key()]” attribute but it doesn’t make sense for it to be used, and which field do I add it to? I am wondering if this sort of table model is even supported?

Answer 1

For M:M relationship you have to create your join (link) class is as below.

public class EmployeeDepartmentLink
{
    [Key, Column(Order = 0)]
    public int EmployeeID;

    [Key, Column(Order = 1)]
    public int DepartmentID;

}

For more information check Create code first, many to many

I hope this will help to you.