Updating disconnected entity that has child entities in linq to sql

Question

In an n-tier application linq-to-sql doesn't seem to have a clear cut solution for updating a disconnected entity that has child EntitySets.

I have some linq-to-sql entities...

public partial class Location : INotifyPropertyChanging, INotifyPropertyChanged
{       
    public int id;      
    public System.Nullable<int> idLocation;     
    public string brandingName;     
    public System.Data.Linq.Binary timeStamp;       
    public EntitySet<LocationZipCode> LocationZipCodes;
}

public partial class LocationZipCode : INotifyPropertyChanging, INotifyPropertyChanged
{
    public string zipcode;      
    public string state;        
    public int idLocationDetail;        
    public int id;      
    public System.Data.Linq.Binary timeStamp;       
    public EntityRef<Location> Location;
}

So a Location entity would have an EntitySet of LocationZipCodes.

The Location domain model gets mapped to a view model which the presentation layer consumes and then ultimately sends back the changed view model entity where it's mapped back to the Location domain model. From there I update the entity and save the changes. Here's the handler:

public class ProgramZipCodeManagerHandler : IHttpHandler {
    private LocationsZipCodeUnitOfWork _locationsZipCodeUnitOfWork = new LocationsZipCodeUnitOfWork();

    public void ProcessRequest(HttpContext context) {
        if (context.Request.HttpMethod == "POST") {
            string json = Json.getFromInputStream(context.Request.InputStream);

            if (!string.IsNullOrEmpty(json)) {
                Location newLocation = Json.deserialize<Location>(json);
                if (newLocation != null) {
                    //this maps the location view model from the client to the location domain model
                    var newDomainLocation = new Mapper<Location, DomainLocation>(new DomainLocationMapTemplate()).map(newLocation);

                    if (newDomainLocation.id == 0)
                        _locationsZipCodeUnitOfWork.locationRepository.insert(newDomainLocation);
                    else
                        _locationsZipCodeUnitOfWork.locationRepository.update(newDomainLocation);

                    _locationsZipCodeUnitOfWork.saveChanges(ConflictMode.ContinueOnConflict);

                    var viewModel = new Mapper<DomainLocation, Location>(new LocationMapTemplate()).map(newDomainLocation);
                    context.Response.ContentType = "application/json";
                    context.Response.Write(Json.serialize(viewModel);
                }
            }
        }       
    }
}

Here is the update method within my locationRepository:

protected System.Data.Linq.Table<T> _table;

public void update(T entity) {
    _table.Attach(entity, true);
    _context.Refresh(RefreshMode.KeepCurrentValues, entity);
}

public void update(T newEntity, T oldEntity) {
    _table.Attach(newEntity, oldEntity);
    _context.Refresh(RefreshMode.KeepCurrentValues, newEntity);
}

I can see that all records directly associated with the Location entity are being updated but the child collection (public EntitySet<LocationZipCode> LocationZipCodes) is not being updated.

Is there a clear cut way of updating a disconnected entity that has a child EntitySet that also needs to be updated? In other words, I have a detached entity that has a collection of another entity. That collection has changed and I need to update that in the database.

Answer 1

No.. you cannot do that.

Attaching and Detaching objects is per the object you working with and will not affect related objects (entities).

You can read further information from here:
Attaching and Detaching Objects

Consider a situation where object A is related to a collection B which is filled with 1000 values. You detach A and send it to some remote processing - A is sent with null in the B relation.. and now A is brought back to your program - there is no way to know that A.B null is a result of the remote processing or was it given to the remote processing already with null.

In the link posted with this answer - please scroll down to read carefully at the section titled:
Considerations for Detaching Objects.