How to write Relationships in Code First?

Yes, Code First Entity Framewok supports relationships like Database First/Relational databases now

Entities :

public class Employee

    {

        [Key]

        public int Eid { get; set; }

        public string Ename { get; set; }

        public string EPhone { get; set; }

        public int Eaddress { get; set; }     

        public Departments Dept { get; set; }

    }

    public class Departments

    {

        [Key]

        public int Did { get; set; }

        public string DName { get; set; }

    }

Here:

Departments----PK table

Employee----Fk table

Primary keys are autogenerated if we send also those are ignored.

Eaddress(reference Departments)à is a reference key of Departments table.  as well we can specify the Department also at a time

Ex:

   Employee eobj = new Employee { Dept = new Departments { DName = "Accounts" },

            Ename = "raju", EPhone = "7171" };

            con.emps.Add(eobj);

            con.SaveChanges();

 

Eid          Ename  EPhone                Eaddress

1              raju        7171       1

Did         DName

1                     Accounts

Employee is automatically mapped to dept of 1

  Employee eobj = new Employee {  Eaddress=1, Ename = "raju1", EPhone = "7172" };

What is use of   public int Eaddress { get; set; }      in Employee ?

New employee -----belongs to existing Department.

Eid          Ename  EPhone                Eaddress

1              raju        7171       1

2              raju1      7172       1  // newly employee added to  existing department.

Did         DName

1                     Accounts

And

We can add new Department aswell new employee at a time.

    Employee eobj = new Employee { Dept = new Departments { DName = "Sales" }, Ename = "balu", EPhone = "4131" };

Eid          Ename  EPhone                Eaddress

1              raju        7171       1

2              raju1      7172       1

3              balu       4131       2

Belongs

Did         DName

1              Accounts

2              Sales

 how to specify keys in Code-First model:

             modelBuilder.Entity<Employee>()

               .HasRequired(a => a.Dept)

               .WithMany()                     --à type of relationship

               .HasForeignKey(u => u.Eaddress);

            //modelBuilder.Entity<Employee>().

                              

            base.OnModelCreating(modelBuilder);

NOTE: keep in mind -à data will be splicted as per columns and stored in their relavent tables.