Entity Code First Cyclic Reference Migrations - ef-code-first

Question

Thanks in advance! I'm having trouble getting a cyclic reference working where EntityA has a nullable foreign key to EntityB and EntityB has a non-nullable (enforced) reference to EntityA. I've created a sample to demonstrate, but I can't get the migrations to have EntityA's refernce to EntityB to be through a foreign key:
public class EntityA
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public EntityB MasterEntityB { get; set; }
public int? MasterEntityBId { get; set; }
}
public class EntityB
{
public string Name { get; set; }
public int Id { get; set; }
public EntityA EntityA { get; set; }
public int AssociationTypeId { get; set; }
}
public class DataContext : DbContext
{
public DataContext()
: base("CyclicTest")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<EntityB>()
.HasRequired(t => t.EntityA)
.WithOptional(a => a.MasterEntityB)
.WillCascadeOnDelete(false);
}
public DbSet<EntityB> Tenants { get; set; }
public DbSet<EntityA> AssociationTypes { get; set; }
}
And here's the migration I get:
public partial class Initial : DbMigration
{
public override void Up()
{
CreateTable(
"dbo.EntityAs",
c => new
{
Id = c.Int(nullable: false, identity: true),
Name = c.String(),
Description = c.String(),
MasterEntityBId = c.Int(),
})
.PrimaryKey(t => t.Id);
CreateTable(
"dbo.EntityBs",
c => new
{
Id = c.Int(nullable: false),
Name = c.String(),
AssociationTypeId = c.Int(nullable: false),
})
.PrimaryKey(t => t.Id)
.ForeignKey("dbo.EntityAs", t => t.Id)
.Index(t => t.Id);
}
public override void Down()
{
DropForeignKey("dbo.EntityBs", "Id", "dbo.EntityAs");
DropIndex("dbo.EntityBs", new[] { "Id" });
DropTable("dbo.EntityBs");
DropTable("dbo.EntityAs");
}
}
I can change the migration manually so it's a foreign key like so:
CreateTable(
"dbo.EntityAs",
c => new
{
Id = c.Int(nullable: false, identity: true),
Name = c.String(),
Description = c.String(),
MasterEntityBId = c.Int(),
})
.PrimaryKey(t => t.Id)
.ForeignKey("dbo.EntityBs", t => t.MasterEntityBId);
CreateTable(
"dbo.EntityBs",
c => new
{
Id = c.Int(nullable: false, identity: true),
Name = c.String(),
EntityAId = c.Int(nullable: false),
})
.PrimaryKey(t => t.Id)
.ForeignKey("dbo.EntityAs", t => t.EntityAId)
.Index(t => t.Id);
But then I find I get an error when I insert an EntityB: "Cannot insert explicit value for identity column in table 'EntityB' when IDENTITY_INSERT is set to OFF."
Again, appreciate the help!
-Max

Answer 1

OK I found the problem. I didn't have a reference for the one to many from A to B via a virtual Collection. That was enough to solve the problem. Plus I've decided to use a sub class for the Master Reference so I don't need a second reference from B back to A for the master instance. That would be null for all other instances and could lead to duplicates breaking the 0 or 1 to 1 intended relationship between MasterB and A. I.e.:
public class EntityA
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
**public ICollection<EntityB> EntityBs { get; set; }**
public MasterEntityB MasterEntityB { get; set; }
public int? MasterEntityBId { get; set; }
}
public class MasterEntityB : EntityB
{
}
public class EntityB
{
public string Name { get; set; }
public int Id { get; set; }
public EntityA EntityA { get; set; }
public int EntityAId { get; set; }
}