Question

假设两个表组和用户如下

[Groups] ([Id] [int] NOT NULL, [Name] [nchar](50) NULL);
[Users] ([Id] [int] NOT NULL, [Name] [nchar](50) NULL, [GroupId] [int] NOT NULL);
FOREIGN KEY([GroupId]) REFERENCES [Groups] ([Id])

其中GroupId是用户的外键。

然后我使用Linq-to-SQL类设计器来创建相关的类，并将以下类添加到项目中

public partial class Group
{
    public override int GetHashCode()
    {
        return (Id.GetHashCode());
    }

    public override bool Equals(object item)
    {
        if ((item == null) || (item is System.DBNull))
            return (false);
        else
        {
            var temp = item as Group;
            if (temp == null)
                return (false);
            else
                if (_Id.Equals(0))
                    return (_Name.Equals(temp.Name));
                else
                    return (_Id == temp.Id);
        }
    }

    partial void OnValidate(System.Data.Linq.ChangeAction action)
    {
        var dc = new DB.DataContext();

        if (action == System.Data.Linq.ChangeAction.Insert)
            if (dc.Groups.Count(o => o.Name.Equals(_Name)) != 0)
                throw new Exception("Name Already Exist On Insert");

        if (action == System.Data.Linq.ChangeAction.Update)
            if (dc.Groups.Count(o => (!o.Id.Equals(_Id) && o.Name.Equals(_Name))) != 0)
                throw new Exception("Name Already Exist On Update");
    }
}

public partial class User
{
    public override int GetHashCode()
    {
        return (Id.GetHashCode());
    }

    public override bool Equals(object item)
    {
        if ((item == null) || (item is System.DBNull))
            return (false);
        else
        {
            var temp = item as User;
            if (temp == null)
                return (false);
            else
                if (_Id.Equals(0))
                    return (_Name.Equals(temp.Name));
                else
                    return (_Id == temp.Id);
        }
    }
}

和

public static DB.Group f1()
{
    DB.DataContext dc = new DB.DataContext();
    if (dc.Groups.Count() == 0)
    {
        DB.Group group = new DB.Group() { Name = "admins" };
        dc.Groups.InsertOnSubmit(group);
        dc.SubmitChanges();
    }
    return dc.Groups.First();
}

public static void f2(DB.Group group, string name)
{
    DB.DataContext dc = new DB.DataContext();
    DB.User user = new DB.User() { Name = name, GroupId = group.Id, };
    dc.Users.InsertOnSubmit(user);
    dc.SubmitChanges();
}

public static void f3(DB.Group group, string name)
{
    DB.DataContext dc = new DB.DataContext();
    DB.User user = new DB.User() { Name = name, Group = group, };
    dc.Users.InsertOnSubmit(user);
    dc.SubmitChanges();
}

现在如果我打电话

DB.Group group = f1();
f2(group, "john");
f2(group, "bob");

然后一切顺利，但如果我打电话

DB.Group group = f1();
f2(group, "john");
f3(group, "bob");

它会抛出异常“插入时已存在名称”。实际上，已调用OnValidate并检测组表的重复名称。奇怪的行为是当要将新用户插入表中时调用OnValidate。这是怎么回事？我犯了错误吗？

Answer 1

我猜是因为你在f3中创建了一个新的DataContext，它假设你想把group作为新记录插入。

您可以手动将组附加到新的DataContext，以便它不会尝试插入它。

public static void f3(DB.Group group, string name)
{
    DB.DataContext dc = new DB.DataContext();
    dc.Groups.Attach(group);
    DB.User user = new DB.User() { Name = name, Group = group, };
    dc.Users.InsertOnSubmit(user);
    dc.SubmitChanges();
}

或者，您可以创建一个DataContext，而不是为每个方法创建一个新的。

Answer 2

Group = group,

在f3中，您将组的实例附加到用户。然后你告诉datacontext插入用户。因为有组连接到用户，并且datacontext当前没有跟踪该组，所以它也假定该组也需要插入。

Linq-to-SQL奇怪的行为

2 个答案: