EF Migrations: The ALTER TABLE statement conflicted with the FOREIGN KEY constraint - entity-framework-5

Question

I had these classes
public class Bid : ...
{
...
[Required]
public virtual TraderUser Trader { get; set; }
}
public class TraderUser : ...
{
...
}
I then changed these classes in the following way and added a new class
public class Bid : ...
{
...
[Required]
public virtual TraderUser TraderUser { get; set; }
}
public class TraderUser : ...
{
...
public int TraderCompanyId { get; set; }
[ForeignKey("TraderCompanyId")]
public virtual TraderCompany TraderCompany { get; set; }
}
public class TraderCompany : ...
{
...
}
When I did an update-database I got the following error
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint
"FK_dbo.Bid_dbo.TraderUser_TraderUser_Id". The conflict occurred in
database "LeasePlan.Development", table "dbo.TraderUser", column 'Id'.
I can't get the database to update. Any help is much appreciated.

Answer 1

Do not know if it is too late, but I had same problem and maybe this could help you.
I cannot see from your post, but probably your TraderUser table has some rows already inserted. What you are trying to accomplish is to create new table TraderCompany and create foreign key relationship in TraderUser that points to TraderCompany table.
In one migration you are trying to create non nullable foreign key relationship for table that already contains data.
You could try to the following:
First migration - everything same, except this line
public int TraderCompanyId { get; set; }
should be
public int? TraderCompanyId { get; set; }
This will allow you to create nullable foreign key column.
Update your TraderCompanyId column for existing data with some row from TraderCompany table.
Second migration - Change code from
public int? TraderCompanyId { get; set; }
to
public int TraderCompanyId { get; set; }
and run your migration.
I hope this will help you.

Answer 2

The alternative is to add an SQL statement within the migration code to insert a row before it adds the foreign keys. Here's an example of what I did:
// Countries is a new table
CreateTable(
"dbo.Countries",
c => new
{
CountryID = c.Int(nullable: false, identity: true),
Name = c.String(),
Currency = c.Int(nullable: false),
})
.PrimaryKey(t => t.CountryID);
// Heres where i insert a row into countries
Sql("INSERT INTO Countries (Name, Currency) VALUES ('United Kingdom', 0)");
// I set the default value to 1 on the ID fields
AddColumn("dbo.Brokers", "CountryID", c => c.Int(nullable: false, defaultValue: 1));
AddColumn("dbo.Products", "CountryID", c => c.Int(nullable: false, defaultValue: 1));
AddForeignKey("dbo.Brokers", "CountryID", "dbo.Countries", "CountryID", cascadeDelete: false);
AddForeignKey("dbo.Products", "CountryID", "dbo.Countries", "CountryID", cascadeDelete: false);
// Migrations then creates index's
CreateIndex("dbo.Brokers", "CountryID");
CreateIndex("dbo.Products", "CountryID");