实体框架更新记录问题（无法为属性调用成员'IsModified'）

Question

I'm having some problems updating a record using Entity Framework 6.

    public bool UpdateOrder(Order order)
    {
        Db.Orders.Attach(order);
        var entry = Db.Entry(order);
        entry.Property(x => x.OrderStatusId).IsModified = true; //Exception thrown
        try
        {
            Db.SaveChanges();
        }
        catch (Exception e)
        {
            logger.Fatal(e);
        }
        return true;
    }

This is the exception message:

Member 'IsModified' cannot be called for property 'OrderStatusId' because the entity of type 'Order' does not exist in the context. To add an entity to the context call the Add or Attach method of DbSet.

I tried changing entry.Property(x => x.OrderStatusId).IsModified = true; to entry.State = EntityState.Modified; But my record does not then get updated. Any ideas how to help?

Apologies if this is obvious but I'm new to using EF and I cannot find how to fix this.

Answer 1

I fixed it by:

public bool UpdateOrder(Order order)
    {
using(var db = DB){
            db.Orders.Attach(order);
            var entry = db.Entry(order);
            entry.Property(x => x.OrderStatusId).IsModified = true; //Exception thrown
            try
            {
                db.SaveChanges();
            }
            catch (Exception e)
            {
                logger.Fatal(e);
            }
            return true;
}
        }

Answer 2

Probably the reason of the exception is the default value in the Id field (primary key) of the "order" object. For int it is 0. In this case "order" is considered as a new object and should be added with "add" method.