The property on type cannot be set because collection is already set to an EntityCollection

Question

I am trying to update an Entity which has navigation property attached to it.

public partial class Stock
{
    #region Primitive Properties

    public virtual int StockId
    {
        get;
        set;
    }

    public virtual string StockName
    {
        get;
        set;
    }

    #endregion

    #region Navigation Properties

    public virtual ICollection<Location> Locations
    ...
}

This works well when I just insert the entity in the Database, but when I update I get the error as:

An exception of type 'System.InvalidOperationException' occurred in EntityFrameworkDynamicProxies-Trade.Sales.Presentation.Admin but was not handled in user code

Additional information: The property 'Locations' on type 'Stock_4654D170FFCE308BB1B9AF1E2018476DF2E1C2E1DBA137F58AB96BCB9FAFC859' cannot be set because the collection is already set to an EntityCollection.

I went through some of the other posts, but the solution which is given is:

Modifying the properties as non-virtual i.e. Removing 'virtual' keyword. However my senior says this cannot be accepted as this class is generated automatically and will change once the Entity is updated from the DB.

Do we have any other solution for this to be worked ?

Answer 1

Definitely there is a line like stock.Locations = myLocationCollection that is causing the problem. What you would like to do is the following:

stock.Locations.Clear(); 
foreach (var loc in myLocationsCollection) 
    stock.Locations.Add(loc); 

It is a workaround that can be used to set the collection as a whole.