Multiple references from one entity to another, database schema, Entity Framework - entity-framework

Question

Read it several times and understood that i'm not so good in asking questions correctly. Made some corrections to the question.
I have 2 classes in my app: Contractor and ContractorGroup.
Each Contractor has a parent Contractor. Parent Contractor can see only it's dependants. And can not see dependants of it's dependants. Only one level of visibility.
Parent Contractor can group it's dependant Contractors into ContractorGroup.
So, many dependant Contractors for one ContractorGroup (many-to-one)
Contractor has a NavProperty ContractorGroup, the group to which it belongs. Each Contractor can be ONLY IN ONE ContractorGroup.
Example:
I'm the parent Contractor and have 5 dependant Contractors and i want to group first 2 of them into 1stContractorGroup and last 3 to 2ndContractorGroup.
So, options to implement:
First: I can not to include FK(VisibleToContractorId - id of my parent Contractor) in ContractorGroup which connects each of 2 groups to parent Contractor.
In this case i can do query similar to:
var ContractorGroupsToDispalayForParentContractor =
context.ContractorGroups.Where(p => p.Contractors.All(p => p.Parent == ParentContractor));
In other words: "Find all groups which consist of contractors with parent == ParentContractor"
In this option everything works fine. DbSchema is simple and clear. But i dont like the query.
Second: Or i can introduce FK(VisibleToContractorId). So one parent Contractor has many ContractorGroups which consist of dependant Contractors. Then i have a simplier and more robust query:
var ContractorGroupsToDispalayForParentContractor =
context.ContractorGroups.Where(p => p.VisibleToContractor == ParentContractor);
This query i like. But EF introduces strange DbColumn which is ALWAYS null. >:-E
Short db schema:
Table("Contractor")
ContractorId = PK
ContractorGroupId = FK
ContractorGroup_ContractorGroupId = FK <--- This One
Table("ContratorGroup")
ContractorGroupId = PK
VisibleToContractorId = FK
My domain Classes and EntityConfiguration:
public class Contractor : IObjectWithState
{
[Key]
public virtual int ContractorId { get; set; }
public virtual Contractor Parent { get; set; }
public virtual int? ParentId { get; set; }
public virtual ContractorGroup ContractorGroup { get; set; }
public virtual int? ContractorGroupId { get; set; }
public virtual ICollection<ContractorGroup> GroupsVisible { get; set; }
}
public class ContractorGroup : IObjectWithState
{
[Key]
public virtual int ContractorGroupId { get; set; }
public virtual Contractor VisibleToContractor { get; set; }
public virtual int? VisibleToContractorId { get; set; }
public virtual ICollection<Contractor> Contractors { get; set; }
}
Entity configurations (only in ContractorGroupConfiguration):
HasMany(p => p.Contractors).WithOptional(p=>p.ContractorGroup);
HasOptional(p => p.VisibleToContractor).WithMany(
p=>p.GroupsVisible).HasForeignKey(p=>p.VisibleToContractorId);
Is it a bug in EF?
What implementation First or Second of domain model would you prefer?
Thanks.

Answer 1

The point is that you need to tell EF that the associations ContractorGroup.VisibleToContractor and Contractor.GroupsVisible are no independent associations (with two FK fields), but are two parts of a bidirectional association. Replace the entity configurations by:
class ContractorConfiguration : EntityTypeConfiguration<Contractor>
{
public ContractorConfiguration()
{
HasMany(c => c.GroupsVisible).WithOptional(g => g.VisibleToContractor);
}
}
Without this, EF creates the field ContractorGroup_ContractorGroupId as a FK for Contractor.GroupsVisible on top of the FK VisibleToContractorId.