Question

有没有更好的方法来编写这样的linq2sql组代码？与T-SQL版本相比似乎太长了，似乎它会在性能方面遇到麻烦。

var Result = (
    // [ 1. JOIN
    from l in db.Lists
    where l.ProfileID == ID
    join item in db.Items on l.ID equals item.ListID into ListItem
    //orderby l.CreateDate descending
    // ] 

    // [ 2. JOIN - 1. GROUPBY
    from l_item in ListItem.DefaultIfEmpty() // left join için
    group l_item by new { 
        l.CategoryID, 
        l.CreateDate,
        l.Header,
        Min_ItemListID = ListItem.Min(c=>c.ListID)
    } into G_List
    join i_photo in db.ItemPhotos on G_List.Key.Min_ItemListID equals i_photo.ItemID into ListItem2
    // ] 

    // [ 2. GROUPBY
    from ll_item in ListItem2.DefaultIfEmpty()
    group ll_item by new {
        G_List.Key.CategoryID, 
        G_List.Key.CreateDate,
        G_List.Key.Header, 
        G_List.Key.Min_ItemListID,
        Min_ItemPhoto_FileName = ListItem2.Min(c=>c.FileName)
    } into GG_List
    // ] 

    select new TList.General_ListViewModel
    {
        CategoryID = GG_List.Key.CategoryID,
        CreateDate = GG_List.Key.CreateDate,
        Header = GG_List.Key.Header,
        FirstImageURL = GG_List.Key.Min_ItemPhoto_FileName
    }
);

Answer 1

我认为你不需要外连接部分，你已经使用组连接分组了所有内容（通过join ... into）。我相信你可以将这个问题简化为：

var query =
    from list in db.Lists
    where list.ProfileID == ID

    join item in db.Items on list.ID equals item.ListID into listItems
    //orderby list.CreateDate descending

    join photo in db.ItemPhotos
        on listItems.Min(c=>c.ListID) equals photo.ItemID into listPhotos

    select new TList.General_ListViewModel
    {
        CategoryID = list.CategoryID,
        CreateDate = list.CreateDate,
        Header = list.Header,
        FirstImageURL = listPhotos.Min(c=>c.FileName),
    };

这个Linq到Sql Group有没有更好的方法

1 个答案: