One-to-many mappings in one entity in EF First code - entity-framework

Question

I have 2 classes :
public class GroupType
{
[Key]
public decimal GroupTypeID { get; set; }
public string Title { get; set; }
public virtual ICollection<Group> Groups { get; set; }
}
and
public class Group
{
[Key]
public decimal GroupID { get; set; }
public string Title { get; set; }
public decimal? GroupParentID { get; set; }
public decimal GroupTypeID { get; set; }
public string FileName { get; set; }
public string GroupCode { get; set; }
public virtual ICollection<GroupType> GroupTypes { get; set; }
public virtual ICollection<Group> MainGroups { get; set; }
}
when I debug project, I get this error:
"Invalid column name 'GroupGroupID'.
"** and **Navigation property
'MainGroups' of
'Parand.DataAccess.Group' cannot be
the inverse of itself.
I want define tree of Group (n layers of groups)
How can I do that it?

Answer 1

This will create the self referencing association in the Group entity:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Group>()
.HasMany(g => g.MainGroups)
.WithOptional()
.HasForeignKey(p => p.GroupParentID);
}
The many to many association between Group and GroupType will be created using a join table so you should remove GroupTypeID property from the Group entity since it will be treated merely as a scalar property and not a Foreign key for this association.