linq to sql复杂查询，分组依据

Question

I have a table called "Articles".

it includes the following field:

ArticleIndex, ArticleLevel, ArticleParentIndex.

I made query which returns all the articles with ArticleLevel=1 - let's call it query1. The query which returns all the articles with ArticleLevel=2 - query2.

I would like to have a query that would return Articles of level=1 with at least one child article (the child articles have level=2), and also the number of child articles.

So far I have the following query:

var filteredItemsGrouped = from i in filteredItems
                           group i by i.ArticleParentIndex into g
                           select new { Node = g, NodeItemsCount = g.Count() };

and then, in order to get the actual articles with level=1 I do:

IList<ArticleNodeInfo> Nodes = new List<ArticleNodeInfo>();
        foreach (var node in filteredItemsGrouped)
        {
            Nodes.Add(new ArticleNodeInfo
            {
                Node = articlesService.GetArticleByIndex((int)(node.Node.FirstOrDefault().ArticleParentIndex)),
                NodeItemsCount = node.NodeItemsCount
            });
        }

This process is too expensive. Is it possible to acheive the same with one query (instead of retreiving by article index every time)?

Hope I'm clear enough...

Answer 1

this should do the trick:

    var articlesLevel1 = (
            from al1 in Articles
            join al2 in Articles on new
            {
                    al1.ArticleIndex,
                    ArticleLevel = 2
            } equals new
            {
                    ArticleIndex = al2.ArticleParentIndex,
                    al2.ArticleLevel
            } into g_al2
            where (al1.ArticleLevel == 1) && g_al2.Any()
            select new
            {
                    ArticlesLevel1 = al1,
                    ArticlesLevel2Count = g_al2.Count()
            });