实体框架添加现有外键

Question

I am having a problem with getting a relationship to work how I would like with Entity Framework. The situation is as follows.

There are a number of departments in a store; food, drink, entertainment, etc.

There are a number of employees who work in a store. Employees are allowed to work in one or more departments.

The classes I have are:

public class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<EmployeeDeparmentMapping> DeparmentMappings { get; set; }
}

public class EmployeeDeparmentMapping
{
    public int Id { get; set; }
    public Employee Employee { get; set; }
    public Department Department { get; set; }

}

I am using code first and my modelbuilder looks something like this

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Employee>().HasMany(e => e.DeparmentMappings).WithRequired(e => e.Employee);

        modelBuilder.Entity<EmployeeDeparmentMapping>().HasRequired(edm => edm.Department);
    }

I am having a problem when I try to add EmployeeDeparmentMappings, like so:

public void SomeMethod(EmployeeDeparmentMapping edm)
{
    MyDbContext myDb = new MyDbContext();
    myDb.EmployeeDepartmentMappings.Add(emd);
    myDb.SaveChanges();
}

The exceptions gets thrown is a PRIMARY KEY violation on the Department table, this is because the department in the EmployeeDepartmentMappings object may already exist in the databse but not in the DbContext.

I tried the following:

public void SomeMethod(EmployeeDeparmentMapping edm)
{
    MyDbContext myDb = new MyDbContext();
    myDb.Departments.Attach(emd.Department);
    myDb.EmployeeDepartmentMappings.Add(emd);
    myDb.SaveChanges();

}

But this throws an InvalidOperationException , the changes get saved to db but the context is apparently broken.

An exception of type 'System.InvalidOperationException' occurred in EntityFramework.SqlServer.dll but was not handled in user code

Additional information: The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: A referential integrity constraint violation occurred: The property values that define the referential constraints are not consistent between principal and dependent objects in the relationship.

What am I doing wrong here??

Answer 1

Try:

public virtual ICollection<EmployeeDeparmentMapping> DeparmentMappings { get; set; }

and

public virtual Employee Employee { get; set; }
public virtual Department Department { get; set; }

virtual because they are just for navigating purposes they already exist