The ALTER TABLE statement conflicted with the FOREIGN KEY constraint - sql-server

Question

When I run the following migration, I am getting the following error:
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint
I have an existing database and refactoring the model to include a navigation property.
See the original model and then the new model:
Original model:
public class Student
{
public int ID { get; set; }
public string Name { get; set; }
public string Country { get; set; }
}
New model:
public class Student
{
public int ID { get; set; }
public string Name { get; set; }
public int CountryID { get; set; }
public virtual Country Country { get; set; }
}
public class Country
{
public int ID { get; set; }
public string Country { get; set; }
}
Add-Migration navigation property:
public override void Up()
{
CreateTable(
"dbo.Countries",
c => new
{
ID = c.Int(nullable: false, identity: true),
CountryName = c.String(),
})
.PrimaryKey(t => t.ID);
AddColumn("dbo.Students", "CountryID", c => c.Int(nullable: false));
CreateIndex("dbo.Students", "CountryID");
AddForeignKey("dbo.Students", "CountryID", "dbo.Countries", "ID", cascadeDelete: true);
DropColumn("dbo.Students", "Country");
}
Update-Database error:
System.Data.SqlClient.SqlException (0x80131904): The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_dbo.Students_dbo.Countries_CountryID". The conflict occurred in database "aspnet-navprop-20141009041805", table "dbo.Countries", column 'ID'.

Answer 1

I got same problem, my table had data therefore I changed foreign key column to nullable.
AddColumn("dbo.Students", "CountryID", c => c.Int(nullable: true));
You should change your code like that then run again Update-Database -Verbose
public override void Up()
{
CreateTable(
"dbo.Countries",
c => new
{
ID = c.Int(nullable: false, identity: true),
CountryName = c.String(),
})
.PrimaryKey(t => t.ID);
AddColumn("dbo.Students", "CountryID", c => c.Int(nullable: true));
CreateIndex("dbo.Students", "CountryID");
AddForeignKey("dbo.Students", "CountryID", "dbo.Countries", "ID", cascadeDelete: true);
DropColumn("dbo.Students", "Country");
}

Answer 2

I had this same issue and truncated the table with the foreign key records and it succeeded.

Answer 3

If there is a data in the table (Student table) delete them and then re-try again.

Answer 4

Against your Student entity you can mark your CountryId property as nullable using a question mark appended to the type, i.e.
public class Student
{
public int ID { get; set; }
public string Name { get; set; }
public int? CountryID { get; set; }
public virtual Country Country { get; set; }
}