Entity Framework 6.1: Code First navigation properties that do not have corresponding keys defined in database

Question

I am trying the Code First approach with EF 6.1 (I'm very new to it) and I have a weird issue with a navigation property based on a 1.1 or 1.0 relationship in the Database.

I have a User class mapped to a User table that looks like:

[Table("TL_MF_SEC_USER_MST")]
public class User
{
    /// <summary>
    /// Table Column : USER_ID
    /// </summary>
    [Key, Column("USER_ID")]
    public decimal ID { get; set; }
    /// <summary>
    /// Table Column : USER_CODE
    /// </summary>
    [Column("USER_CODE")]
    public string Code { get; set; }
    /// <summary>
    /// Table Column : DOMAIN_NM
    /// </summary>
    [Column("DOMAIN_NM")]
    public string Domain { get; set; }
    /// <summary>
    /// Table Column : EMPLOYEE_ID
    /// </summary>
    [Column("EMPLOYEE_ID")]
    public string EmployeeID { get; set; }

And an Employee class mapped to an Employee table that looks like:

[Table("TL_MF_EMPLOYEE_MST")]
public class Employee
{
    /// <summary>
    /// Table Column : EMPLOYEE_CODE
    /// </summary>
    [Key, Column("EMPLOYEE_CODE")]
    public string EmployeeID { get; set; }
    /// <summary>
    /// Table Column : EMPLOYEE_NAME
    /// </summary>
    [Column("EMPLOYEE_NAME")]
    public string EMPLOYEE_NAME { get; set; }

    public string Manager { get; set; }

The problem is that the "Keys" between these tables are the EmployeeID property (not a primary key) from the User class which maps to the EmployeeID property (which is also not a primary or foreign key in the DB) in the Employee class.

Thus, I am trying to create a navigation property on User to Employee but I cannot figure out how to tell EF to use these two non-key fields as the properties to match the user on.

Unfortunately, I am in an environment where I probably can't make significant changes to the actual database schema as this structure is used for administering permissions in at least 8 apps (some of which have 20 plus instances). Some small changes (like adding an index or constraint) might work though.

If there is a way to do this via attributes or fluent api, I would really appreciate a heads up. Any recommendations are welcome.

Thanks in advance.

Answer 1

EF only accepts associations to primary key properties. But it only looks at primary keys defined in the model. So, because of the Key attribute on EmployeeID , you can use it in associations, like so:

public class User
{
    [Key, Column("USER_ID")]
    public decimal ID { get; set; }

    ...

    [Column("EMPLOYEE_ID")]
    public string EmployeeID { get; set; }

    public Employee Employee { get; set; } // You need this property
}

And in the context's override of OnModelCreating :

modelBuilder.Entity<User>()
            .HasRequired(u => u.Employee) // Or HasOptional
            .WithMany()
            .HasForeignKey(u => u.EmployeeId);

Apparently, seeing this Key attribute on EmployeeID , you are certain that EmployeeID is a candidate key to Employee . This must be absolutely guaranteed for this to work correctly.

It's clear that you use code-first without migrations. With migrations, this mapping would of course create a primary key EmployeeId in the database.