Entity Framework many-to-many generic Update

Question

I'm trying to implement a generic many-to-many Update method using EF6. Every time I try to update the navigation property, I get an exception:

"Violation of PRIMARY KEY constraint 'PK_dbo.Classes'. Cannot insert duplicate key in object 'dbo.Classes'. The duplicate key value is (698d5483-eb48-4d7e-84e7-a9f95a243d3d).\r\nThe statement has been terminated."

How can I fix it?

public void Update(T entity, params Expression<Func<T, IEnumerable>>[] navProps)
{
    using (var context = new Context())
    {
        T foundEntity = context.Set<T>().Find(entity.Id);
        var entry = context.Entry(foundEntity);
        entry.CurrentValues.SetValues(entity);

        foreach (var prop in navProps)
        {
            string memberName;
            var member = prop.Body as MemberExpression;

            if (member != null)
            {
                memberName = member.Member.Name;
            }
            else
            {
                throw new Exception();
            }

            var collection = entry.Collection(memberName);
            collection.Load();
            collection.CurrentValue = typeof(T).GetProperty(memberName).GetValue(entity);
        }

        context.SaveChanges();
    }
}

You need to update your object graph. you should introduce all deleted, added and modified child entities to the context and this is not a trivial task. You may find this [step by step answer](http://stackoverflow.com/a/33509039/3110834) helpful. — Reza Aghaei, Dec 18 '15 at 21:05
There is a tool for what you're trying to achieve: GraphDiff. — Gert Arnold, Dec 20 '15 at 09:16

score 0 · Answer 1 · answered Dec 25 '15 at 12:45

Finally I have found a solution for generic many-to-many update

 public void Update(Guid id, T record)
        {
            using (var context = new FortisDataStoreContext(_client, _user))
            {
                var set = context.Set<T>().AsQueryable();

                foreach (var x in GetNavigationProperties(context, record))
                {
                    foreach (var xx in x.PropertyType.GetGenericArguments())
                    {
                        set = set.Include(x.Name);
                    }
                }

                var entry = set.FirstOrDefault(x => x.Id == id && x.IsClosed == false);
                context.Entry(entry).CurrentValues.SetValues(record);

                foreach (var x in GetNavigationProperties(context, record))
                {
                    if(x.PropertyType.GetGenericArguments().Count() > 0)
                    {
                        var genericType = x.PropertyType.GenericTypeArguments[0];
                        var newValues = (IList)x.GetValue(record, null) ?? new object[0];
                        var genericList = CreateList(genericType);
                        foreach (var item in newValues)
                        {
                            var ident = item.GetType().GetProperty("Id").GetValue(item, null);
                            var obj = context.Set(genericType).Find(ident);
                            genericList.Add(obj);
                        }
                        context.Entry(entry).Collection(x.Name).CurrentValue = genericList;
                    }
                }

                context.SaveChanges();
            }
        }

Entity Framework many-to-many generic Update

1 Answers1