mac var从linq到某个实例

products oneProduct = (from p in db.products
                      where p.number == 640
                      select p).FirstOrDefault();

或

products oneProduct = db.products.FirstOrDefault(p => p.number == 640);

您不能将DB中的实例映射到刚刚创建的实例。您可以将对DB实例的引用保存到您的数据库,即替换:

 products produkt1 = new products(); // points to the first instance
 produkt1 = query.FirstOrDefault(...); // now points to the second instance. if this was the last reference, object probably will be deleted by GC soon

class products
{
    public void CloneFrom(products source)
    {
        this.SomeThing = source.SomeThing;
        ...
    }
}

在大多数情况下,这是一个坏主意,愚蠢的做法。

products produkt1 =  db.products.FirstOrDefault(p => p.number == 640);

为什么不编辑所选实体(oneProduct)?

您能详细说明一下您的意图是什么吗?是否要创建所选实体的副本,以便将新副本作为新行插入?