Why is my EF detaching not enough?

Question

I try to detach an entity of type group.

Actucally I save it in my cache, and detach it a moment before responding the client.

On the next request I get the group from the cache and re-attch a new objectContext.

However I get An entity object cannot be referenced by multiple instances of IEntityChangeTracker

I know attach includes all related entities but detach doesn't. There I have to detach every related entity.

What am I missing in my detach?

here is my entities hirarchy:

public partial class App
{
    public App()
    {
        this.Pairs = new HashSet<Pair>();
    }

    public string AppName { get; set; }
    public System.Guid AppGuid { get; set; }
    public string ClientAppID { get; set; }
    public bool IsDeleted { get; set; }
    public Nullable<System.DateTime> CreatedDate { get; set; }
    public Nullable<System.DateTime> UpdatedDate { get; set; }

    public virtual AppsData AppsData { get; set; }
    public virtual ICollection<Pair> Pairs { get; set; }
}


public partial class AppsData
{
    public System.Guid AppGuid { get; set; }
    public string Url { get; set; }
    public string DisplayName { get; set; }
    public string AppDesc { get; set; }
    public string PrivacyPolicyUrl { get; set; }
    public string TermsOfUseUrl { get; set; }
    public string LocalizationKey { get; set; }
    public string Compatibility { get; set; }
    public bool HiddenApp { get; set; }
    public bool IsExperimental { get; set; }

    public virtual App App { get; set; }
}

public partial class Browser
{
    public Browser()
    {
        this.BrowserVersions = new HashSet<BrowserVersion>();
    }

    public int BrowserID { get; set; }
    public string BrowserName { get; set; }
    public string BrowserCode { get; set; }

    public virtual ICollection<BrowserVersion> BrowserVersions { get; set; }
}

public partial class BrowserVersion
{
    public BrowserVersion()
    {
        this.BrowserVerToCriterias = new HashSet<BrowserVerToCriteria>();
    }

    public System.Guid BrowserVersionID { get; set; }
    public int BrowserID { get; set; }
    public string Version { get; set; }
    public System.DateTime CreatedDate { get; set; }
    public System.DateTime UpdatedDate { get; set; }
    public Nullable<int> Group_Id { get; set; }

    public virtual Browser Browser { get; set; }
    public virtual ICollection<BrowserVerToCriteria> BrowserVerToCriterias { get; set; }
}

public partial class BrowserVerToCriteria
{
    public System.Guid CriteriaID { get; set; }
    public System.Guid BrowserVersionID { get; set; }
    public string ConditionBrowserVersion { get; set; }

    public virtual BrowserVersion BrowserVersion { get; set; }
    public virtual Criterion Criterion { get; set; }
}

public partial class CommonConfig
{
    public int ID { get; set; }
    public string NAME { get; set; }
    public string VALUE { get; set; }
    public System.DateTime CREATED_DATE { get; set; }
    public System.DateTime UPDATED_DATE { get; set; }
    public byte GROUP_ID { get; set; }
    public string DESCRIPTION { get; set; }
}

public partial class Country
{
    public Country()
    {
        this.Criteria = new HashSet<Criterion>();
        this.Criteria1 = new HashSet<Criterion>();
    }

    public int CountryID { get; set; }
    public string CountryCode { get; set; }
    public string CountryName { get; set; }

    public virtual ICollection<Criterion> Criteria { get; set; }
    public virtual ICollection<Criterion> Criteria1 { get; set; }
}

    public Criterion()
    {
        this.BrowserVerToCriterias = new HashSet<BrowserVerToCriteria>();
        this.Countries = new HashSet<Country>();
        this.CountriesExceptions = new HashSet<Country>();
        this.Pairs = new HashSet<Pair>();
    }

    public System.Guid CriteriaID { get; set; }
    public string Domains { get; set; }
    public System.DateTime CreatedDate { get; set; }
    public System.DateTime UpdatedDate { get; set; }
    public string DomainsExclude { get; set; }

    public virtual ICollection<BrowserVerToCriteria> BrowserVerToCriterias { get; set; }
    public virtual ICollection<Country> Countries { get; set; }
    public virtual ICollection<Country> CountriesExceptions { get; set; }
    public virtual ICollection<Pair> Pairs { get; set; }
}

public partial class CTID
{
    public string CTID1 { get; set; }
    public string AppVersion { get; set; }
}

public partial class CtidPgPastExistence
{
    public string Ctid { get; set; }
}

public partial class Group
{
    public Group()
    {
        this.Pairs = new HashSet<Pair>();
    }

    public System.Guid GroupId { get; set; }
    public int TestId { get; set; }
    public int IdInTest { get; set; }
    public bool WelcomeExperienceEnabledByDefault { get; set; }

    public virtual MamConfiguration MamConfiguration { get; set; }
    public virtual ICollection<Pair> Pairs { get; set; }
}

public partial class MamConfiguration
{
    public MamConfiguration()
    {
        this.Groups = new HashSet<Group>();
        this.MamConfigurationCTIDs = new HashSet<MamConfigurationCTID>();
    }

    public int TestID { get; set; }
    public string TestName { get; set; }
    public string Description { get; set; }
    public int StatusId { get; set; }
    public System.DateTime CreatedDate { get; set; }
    public System.DateTime UpdatedDate { get; set; }
    public bool IsProd { get; set; }
    public int TestTraffic { get; set; }

    public virtual ICollection<Group> Groups { get; set; }
    public virtual MamConfigurationStatus MamConfigurationStatus { get; set; }
    public virtual ICollection<MamConfigurationCTID> MamConfigurationCTIDs { get; set; }
}

public partial class MamConfigurationCTID
{
    public int TestID { get; set; }
    public string CTID { get; set; }

    public virtual MamConfiguration MamConfiguration { get; set; }
}

public partial class MamConfigurationStatus
{
    public MamConfigurationStatus()
    {
        this.MamConfigurations = new HashSet<MamConfiguration>();
    }

    public int StatusId { get; set; }
    public string Status { get; set; }

    public virtual ICollection<MamConfiguration> MamConfigurations { get; set; }
}

public partial class Pair
{
    public Pair()
    {
        this.Groups = new HashSet<Group>();
    }

    public System.Guid PairID { get; set; }
    public System.Guid CriteriaID { get; set; }
    public System.Guid AppGuid { get; set; }

    public virtual App App { get; set; }
    public virtual Criterion Criterion { get; set; }
    public virtual ICollection<Group> Groups { get; set; }
}

public partial class SettingsServicesConfig
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string URL { get; set; }
    public int Interval { get; set; }
    public System.DateTime UPDATED_DATE { get; set; }
    public System.DateTime CREATED_DATE { get; set; }
    public int GROUP_ID { get; set; }
}

here is my detach function:

public void Detach<T>(MaMDBEntities maMdbEntities, T item) where T : class, new()
{
    switch (typeof (T).Name.ToLower())
    {
        case "group":
            {
                var group = item as Group;

                if (group == null)
                {
                    mApplicationLogger.Error(string.Format("Couldn't cast item to type 'Group'"));

                    throw new InvalidCastException(string.Format("Couldn't cast item to type 'Group'"));
                }

                DetachState(maMdbEntities, group.MamConfiguration);

                foreach (var pair in group.Pairs.ToList())
                {
                    DetachState(maMdbEntities, pair.App);

                    DetachState(maMdbEntities, pair.App.AppsData);

                    foreach (var country in pair.Criterion.Countries.ToList())
                    {
                        DetachState(maMdbEntities, country);
                    }

                    foreach (var country in pair.Criterion.CountriesExceptions.ToList())
                    {
                        DetachState(maMdbEntities, country);
                    }


                    foreach (var browserVerToCriterias in pair.Criterion.BrowserVerToCriterias.ToList())
                    {
                        DetachState(maMdbEntities, browserVerToCriterias.BrowserVersion.Browser);

                        DetachState(maMdbEntities, browserVerToCriterias.BrowserVersion);

                        DetachState(maMdbEntities, browserVerToCriterias);
                    }

                                                DetachState(maMdbEntities, pair.Criterion);

                    DetachState(maMdbEntities, pair);

                }

                break;
            }
    }
    maMdbEntities.Entry(item).State = EntityState.Detached;
}

private static void DetachState(MaMDBEntities maMdbEntities, object item)
{
    maMdbEntities.Entry(item).State = EntityState.Detached;
}

Answer 1

I believe that you need to make sure that none of the entities which remain in your context, reference any of those which have been detached. So if say, something else references a detached instance of Pair, the context will quite happily find it, traverse its navigation properties and add the whole lot back in.

Rather than setting the State property have you tried:

((IObjectContextAdapter)maMdbEntities).ObjectContext.Detach(item);

This is supposed to detach any links to the item being detached in addition to the item itself.

EDIT

Ok, lets look at the "detach any links to the item being detached ...", ObjectContext.Detach ultimately calls this method:

// System.Data.Objects.EntityEntry
internal void Detach()
    {
    base.ValidateState();
    bool flag = false;
    RelationshipManager relationshipManager = this._wrappedEntity.RelationshipManager;
    flag = (base.State != EntityState.Added && this.IsOneEndOfSomeRelationship());
    this._cache.TransactionManager.BeginDetaching();
    try
        {
        relationshipManager.DetachEntityFromRelationships(base.State);
        }
    finally
        {
        this._cache.TransactionManager.EndDetaching();
        }
    this.DetachRelationshipsEntries(relationshipManager);
    IEntityWrapper wrappedEntity = this._wrappedEntity;
    EntityKey entityKey = this._entityKey;
    EntityState state = base.State;
    if (flag)
        {
        this.DegradeEntry();
        }
    else
        {
        this._wrappedEntity.ObjectStateEntry = null;
        this._cache.ChangeState(this, base.State, EntityState.Detached);
        }
    if (state != EntityState.Added)
        {
        wrappedEntity.EntityKey = entityKey;
        }
    }

DetachEntityFromRelationships breaking down all the links. The documentation on ObjectContext.Detach is not specific about the tearing down of links http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.detach.aspx it does say "After the Detach method is called, the system will no longer keep references that point to this object and it can be collected by the garbage collector", which implies all LinkDescriptors will also have been removed.

With regards your 3rd comment "Do you think IObjectContextAdapter will enable full detachment. Or there will always be other object in context that I will misss and not detach?" there are two things here; there is the property of the object and the LinkDescriptor which the context uses to track to the relationship. Detach merely stops tracking an object's relationships by detaching the LinkDescriptors, it doesn't detach the object at the other end of the relationship. Neither does it set such properties to null, if you inspect the object after detaching it will still have those properties set.

Is this the best approach? Detaching and reattaching is difficult to get right. If you need to detach and reattach I would suggest you move your deep detach rountines into the classes themselves rather than in a generic method.

That said, you wrote "On the next request I get the group from the cache..." which leads to me wonder what would be the longest period of time between two requests? Could you be introducing concurrency issues by caching? Are you hosting your WCF service in IIS? Could you use IIS's caching if concurrency will not be a problem? Are you handling all requests on the same thread? You might not be aware that ObjectContext instance methods are not thread safe.