执行多个 LINQ 更新以避免 uniquekey 异常

Question

我有一个数据库，其列 ParentRef 和 SortIndex 上有唯一键。

在 LINQ 中，我想切换两个 SortIndex 值。我想在一笔交易中完成此操作，这样可以同时有多个用户。如何使用 LINQ 一次性切换值，以便我的 Unique 键不被侵犯？

        var dc = new MyDataContext();

        using (TransactionScope trans = new TransactionScope())
        {
            var pageToBeMoved = dc.Pages.Where(p => p.ID == id).Single();
            var pageToBeSwitched = (from p in dc.Pages
                                    where p.ParentRef == pageToBeMoved.ParentRef
                                    where p.SortIndex > pageToBeMoved.SortIndex
                                    orderby p.SortIndex ascending
                                    select p).First();

            int tempSortIndex = pageToBeMoved.SortIndex;

            pageToBeMoved.SortIndex = pageToBeSwitched.SortIndex;
            pageToBeSwitched.SortIndex = tempSortIndex;

            dc.SubmitChanges();

            trans.Complete();
        }

Answer 1

我认为要切换唯一键值，您可能需要在切换期间使用第三个临时值，即：

• create new value
• set page2.SortIndex to new value
• set page1.SortIndex to old page2.SortIndex
• set page2.SortIndex to old page1.SortIndex

...否则您可能会在切换过程中遇到唯一的键冲突。

沿着这些思路：

    var dc = new MyDataContext();

    using (TransactionScope trans = new TransactionScope())
    {
        var pageToBeMoved = dc.Pages.Where(p => p.ID == id).Single();
        var pageToBeSwitched = (from p in dc.Pages
                                where p.ParentRef == pageToBeMoved.ParentRef
                                where p.SortIndex > pageToBeMoved.SortIndex
                                orderby p.SortIndex ascending
                                select p).First();

        int oldMSortIndex = pageToBeMoved.SortIndex;
        int oldSSortIndex = pageToBeSwitched.SortIndex;
        // note: here you need to use some value that you know will not already 
        // be in the table ... maybe a max + 1 or something like that
        int tempSortIndex = someunusedvalue;

        pageToBeMoved.SortIndex = tempSortIndex;
        dc.SubmitChanges();
        pageToBeSwitched.SortIndex = oldMSortIndex;
        dc.SubmitChanges();
        pageToBeMoved.SortIndex = oldSSortIndex;
        dc.SubmitChanges();
    }