EF Return next value from a non-generic dbset

Question

All my tables in the database has a columns named "r_e_c_n_o_", isn´t an autoincremented column, and there is no possibility to change it. Its our ERP database, from a third company and they use their aproach to create the database.

So... what I need is a generic method to increment a value in savechanges() method automatically, currently I´m using the follow method below:

    public static int GetNextRecno<T>(this DbContext context) where T : DadosadvEntityBase
    {
        lock (_locker)
        {
            var typeName = typeof(T).FullName;
            int next = 1;
            if (lastRecnos.ContainsKey(typeName))
            {
                int lastRecno = lastRecnos[typeName];
                next = lastRecno + 1;
            }
            else
            {
                next = context.Set<T>().Max(x => x.Recno) + 1;
            }
            lastRecnos[typeName] = next;
            return next;
        }

And I´d like to achieve the same using a non-generic type, something like (look the commented line):

    public static int GetNextRecno(this DbContext context, Type entityType) 
    {
        lock (_locker)
        {
            var typeName = entityType.FullName;
            int next = 1;
            if (lastRecnos.ContainsKey(typeName))
            {
                int lastRecno = lastRecnos[typeName];
                next = lastRecno + 1;
            }
            else
            {
                //here is the problem with a non-generic type, I have no idea how to get next value in this case
                next = context.Set<T>().Max(x => x.Recno) + 1;
            }
            lastRecnos[typeName] = next;
            return next;
        }

Answer 1

You can make an instance of entityType and then call your original generic extension method:

public static int GetNextRecno(this DbContext context, Type entityType) 
{
    //create an instance of entityType
    dynamic instance = Activator.CreateInstance(entityType);
    return GetNextRecno(context, instance);
}

//note this is not an extension method
public static int GetNextRecno<T>(DbContext context, T instance) 
{
    //call your original generic extension method
    return context.GetNextRecno<T>();
}