c# - 将实体的状态设置为已删除会将实体从 dbContext 中删除

Question

我对 Entity Framework 比较陌生。最近我遇到了这种奇怪的行为(在我看来)，这让我很困惑。

如果我将其状态设置为已删除，为什么被跟踪的实体会从 dbContext 中删除？

例如:

var customers = db.Customers
.Where(customer => customer.FirstName.Contains("John"))
.Take(10)
.ToList();

//Let's iterate through the customers -list
//and remove the 5th customer
int i = 1;
foreach(var customer in customers)
{
    if(i == 5)
    {
        //An exception will be thrown
        db.Entry(customer).State = EntityState.Deleted;
    }
    i++;
}

当第 5 个客户的状态从 Unchanged 更改为 Deleted 时，整个对象将从上下文中甚至从 customers 中销毁 -列表。更糟糕的是:这也会引发异常，因为此操作会更改我们正在迭代的列表!

谁能向我解释为什么在通过调用 db.SaveChanges() 将更改保存到数据库之前会发生这种情况？

Answer 1

Why does tracked entity gets removed from the dbContext if I set it's state to Deleted?

为了防止像这样非常奇怪的事情......

foreach(var customer in customers)
{
    db.Entry(customer).State = EntityState.Deleted;
}

foreach(var customer in customers)
{
    Console.WriteLine("I'm a deleted customer that still exists");
}

由此产生的后果将迫使我们编写这样的代码。

foreach(var customer in customers)
{
    //Extra code to make sure nothing deleted is in here
    if(db.Entry(customer).State != EntityState.Deleted)
    {
       //Do work
    }
}

请注意，该对象仍然存在于 ObjectStateManager 中，但与对象图的任何正常交互都不会产生任何已删除的对象。你仍然可以看到它像这样存在......

var customer = customers.First();
db.Entry(customer).State = EntityState.Deleted;
Console.WriteLine(db.Entry(customer).State.ToString()); //Deleted