Handling Related Data when using Entity Framework Code First - entity-framework

Question

I have two Classes: LicenseType and EntityType.
[Table("LicenseType")]
public class LicenseType : ComplianceBase, INotifyPropertyChanged
{
private List<Certification> _certifications = new List<Certification>();
private List<EntityType> _entityTypes = new List<EntityType>();
public List<EntityType> EntityTypes
{
get { return _entityTypes; }
set { _entityTypes = value; }
}
public List<Certification> Certifications
{
get { return _certifications; }
set { _certifications = value; }
}
}
and
[Table("EntityType")]
public class EntityType : ComplianceBase, INotifyPropertyChanged
{
private List<LicenseType> _licenseTypes = new List<LicenseType>();
public List<LicenseType> LicenseTypes
{
get { return _licenseTypes; }
set
{
_licenseTypes = value;
// OnPropertyChanged();
}
}
}
The both derive from ComplianceBase,
public class ComplianceBase
{
private int _id;
private string _name;
private string _description;
public string Description
{
get { return _description; }
set
{
if (_description == value) return;
_description = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
public int Id
{
get { return _id; }
set
{
if (value == _id) return;
_id = value;
OnPropertyChanged();
}
}
public string Name
{
get { return _name; }
set
{
if (value == _name) return;
_name = value;
OnPropertyChanged();
}
}
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
What I want is to be able to do is associate an EntityType with one or more LicenseTypes, so for instance, an EntityType "Primary Lender" could be associated with say two LicenseTypes, "Lender License" and "Mortgage License". In this situation, I want one record in the EntityType table, "Primary Lender" and two records in my LicenseType table: "Lender License" and "Mortgage License".
The code for adding related LicenseTypes to my EntityType is done by calling:
_currentEntity.LicenseTypes.Add(licenseType);
and then calling _context.SaveChanges();
There is an additional table, "EntityTypeLicenseTypes" that serves as the lookup table to relate these two tables. There are two records to join the EntityType with the two related LicenseTypes.
And this works. However, my code also adds (it duplicates) the LicenseType record and adds it in the LicenseType table for those records that are being associated.
How can I stop this from happening?

Answer 1

In order to avoid the duplication you must attach the licenseType to the context:
_context.LicenseTypes.Attach(licenseType);
_currentEntity.LicenseTypes.Add(licenseType);
_context.SaveChanges();