EF POCO's can't update navigation property - entity-framework

Question

I'm using EF5 with MVC and POCO's and need a little help
I have an update function which is passed a disconnected POCO. The POCO has a 'navigation property' collection, eg: Provider has
public virtual ICollection<Company> Companies { get; set; }
When the Provider was loaded (and the old context closed) it had two Company objects, now it has four and I'd like to update.
I thought the code below might work but Companies is not updated (but the non-navigational properties of Provider (like string Name {get;set} are still updated ok) and there is no error
public void Update(Provider entity)
{
// Existing entity
_context.Entry(entity).State = EntityState.Modified;
if (entity.Companies.Any())
{
//try to tell EF about the companies
foreach (var company in entity.Companies)
{
//the company exists already - let the context know....
_context.Entry(company).State = EntityState.Modified;
_context.Companies.Attach(company);
}
}
}
... and later: _unitOfWork.SaveChanges();
For an insert of Provider with Companies I had successfully used:
if (entity.Companies.Any())
{
//these are not to be created - they exist -
//I want EF to add them as nav properties
foreach (var company in entity.Companies)
{
//the company exists already - let the context know....
_pvpContext.Companies.Attach(company);
}
}
// New entity
_pvpContext.Entry(entity).State = EntityState.Added;
I'm going to go and read Julia Lerman's book as EF is killing me - but I'd really appreciate any help updating 'Companies' in the meantime - Thx
Edit:
Taking #Manos' kind advice I tried:
List<Company> companies = new List<Company>();
if (entity.Companies != null && entity.Companies.Any())
{
//pull out the Companies from the POCO
companies = entity.Companies.ToList();
//remove them
entity.Companies = new Collection<Company>();
entity.Companies.Clear();
}
// pass existing entity to the context, tagged as modified
_pvpContext.Entry(entity).State = EntityState.Modified;
if (companies.Any())
{
//now re-add the companies while the context is listening. ffs.
foreach (var company in companies)
{
entity.Companies.Add(company);
}
}
If I add the Provider.Companies to the context (like in the insert) I get:
Violation of PRIMARY KEY constraint 'PK__tmp_ms_x__679519B7F943FD8D'.
Cannot insert duplicate key in object 'dbo.ProviderCompany'. The
duplicate key value is (5, 3)
which is odd as there is not composite key of (provider 5, company 3) - so maybe it's trying to add it in twice here?
If I don't pre-add the Provider.Companies I get:
at System.Data.Entity.Internal.InternalContext.SaveChanges() at
System.Data.Entity.Internal.LazyInternalContext.SaveChanges() at
System.Data.Entity.DbContext.SaveChanges()

Answer 1

I only have 4.1 to test, but try this as a basic logic:
public void Update(Provider entity)
{
// Existing entity
Provider contextProvider = _context.Entry(entity);
contextProvider.Companies.Clear();
foreach (var company in entity.Companies)
{
contextProvider.Companies.Add(company);
}
}
This needs a little refinement in order to only add new companies as opposed to doing a complete removal and reinstatement but it should work.
Edit in response to comment:
Try catching the exception thrown by SaveChanges() with the following:
try {
_unitOfWork.SaveChanges();
} catch (System.Data.Entity.Validation.DbEntityValidationException e) {
foreach (var k in e.EntityValidationErrors) {
foreach (var e1 in k.ValidationErrors) {
Console.WriteLine("{0} - {1}", e1.PropertyName, e1.ErrorMessage);
}
}
}
It should give you a little more information to go on.