What does entity.Items.Clear() do in EF? - entity-framework

Question

In a project I'm working on, whenever I call SaveChanges() after clearing list of items, I get this error:
The operation failed: The relationship could not be changed because
one or more of the foreign-key properties is non-nullable. When a
change is made to a relationship, the related foreign-key property is
set to a null value. If the foreign-key does not support null values,
a new relationship must be defined, the foreign-key property must be
assigned another non-null value, or the unrelated object must be
deleted.
I have these two classes with one to many relationship (simplest implementation):
public class Company
{
public int Id {get; set;}
public string Name {get; set;}
public virtual List<Vehicle> Vehicles {get; set;}
}
public class Vehicle
{
public int Id {get; set;}
public string Model {get; set;}
}
I'm guessing that calling company.Vehicles.Clear() should update the auto generated column Company_Id in the Vehicle table, setting its value to null, but that not seems the case which the error above indicating.
So I'me wondering what exactly company.Vehicles.Clear() do in the database side?
EDIT
Thanks to the answer by #McKabue and the link he provided, I found this is the solution, this is the complete code:
var company = context.Set<GENCompany>().
Include(m => m.Vehicles).
Include(m => m.Quotes).
Include(m => m.Phones).
Include(m => m.Persons).
Include(m => m.Leads).
Include(m => m.Emails).
Include(m => m.Drivers).
Include(m => m.Deals).
Include(m => m.Comments).
Include(m => m.Branches).
Include(m => m.Addresses).
SingleOrDefault(m => m.Id == companyModel.Id);
context.Entry(company).State = EntityState.Modified;
company.Vehicles.Clear();
company.Drivers.Clear();
company.Quotes.Clear();
company.Persons.Clear();
company.Leads.Clear();
company.Deals.Clear();
company.Branches.Clear();
var phones = context.CompanyPhones.Where(x => x.CompanyId == companyModel.Id);
context.CompanyPhones.RemoveRange(phones);
var emails = context.CompanyEmails.Where(x => x.CompanyId == companyModel.Id);
context.CompanyEmails.RemoveRange(emails);
var comments = context.CompanyComments.Where(x => x.CompanyId == companyModel.Id);
context.CompanyComments.RemoveRange(comments);
var addresses = context.CompanyAddresses.Where(x => x.CompanyId == companyModel.Id);
context.CompanyAddresses.RemoveRange(addresses);
For some entities they are removed using .Clear() syntax, other entities are removed by fetching their records and deleteing them all (not only the relation). It makes perfect sense in the current design, for example in the create page of the company, the phone data is added manually, while vehicles are selected from drop down menu, while it makes this perfect sense I feel so confused to determine why this happen, for example here is the CompanyPhone class:
public class GENCompanyPhone
{
[Key]
public long PhoneId { get; set; }
public long CompanyId { get; set; }
public long PhoneTypeId { get; set; }
public DateTime DateCreated { get; set; } = DateTime.Now;
public DateTime DateUpdated { get; set; } = DateTime.Now;
public Guid? CreatedById { get; set; }
public bool IsPublish { get; set; } = false;
public bool IsActive { get; set; } = false;
[MaxLength(255)]
[Index(IsUnique = true)]
public string PhoneNumber { get; set; }
[ForeignKey("CompanyId")]
public virtual GENCompany Company { get; set; }
}
on the other hand this is the vehicle class:
public class GENVehicle
{
public long Id { get; set; }
public long? BrandId { get; set; }
[ForeignKey("BrandId")]
public GENBrand Brand { get; set; }
public string Model { get; set; }
public DateTime? LicenseIssueDate { get; set; }
public Guid? CreatedById { get; set; }
[ForeignKey("VehicleTypeId")]
public virtual GENVehicleType VehicleType { get; set; }
public long? VehicleTypeId { get; set; }
public long? LicenseIssuerId { get; set; }
[ForeignKey("LicenseIssuerId")]
public GENEmployee LicenseIssuer { get; set; }
}
I can't determine exactly why EF deal differently with Vehicle and CompanyPhone

Answer 1

It means that you are clearing a record that is referenced in another table. So, EF warns you...there are ways you can avoid this by setting Cascade delete
Edit
To remove child elements from a parent table, the children entities need to be loaded.
Edit 2
var company = context.Set<GENCompany>().Where(m => m.Id == companyModel.Id);
Include(m => m.Vehicles).
Include(m => m.Quotes).
Include(m => m.Phones).
Include(m => m.Persons).
Include(m => m.Leads).
Include(m => m.Emails).
Include(m => m.Drivers).
Include(m => m.Deals).
Include(m => m.Comments).
Include(m => m.Branches).
Include(m => m.Addresses).SingleOrDefault();
company.Vehicles.Clear();
company.Drivers.Clear();
company.Quotes.Clear();
company.Persons.Clear();
company.Leads.Clear();
company.Deals.Clear();
company.Branches.Clear();
THAT WILL WORK
Query before Including
Include All entities you want to remove;
Clear / RemoveRange / Remove one by one from the parent (company object)