Linq To Sql中實現Left Join與Inner Join使用Linq語法與lambda表達式

當前有兩個表，sgroup與sgroupuser，二者經過gKey關聯，而sgroup表記錄的是組，而sgroupuser記錄是組中的用戶，所以在sgroupuser中不必定有數據。須要使用Left Join獲取數據：

Linq語法以下:

var sg = (from g in dc.sgroup
                     join gu in dc.sgroupuser on g.gKey equals gu.gKey into l
                     from lgu in l.DefaultIfEmpty()
                      select new { g, lgu }).ToList();

Lambda表達式以下：

var sg = dc.sgroup.GroupJoin(dc.sgroupuser, g => g.gKey, gu => gu.gKey, (g, gu) => new { g, gu }).Select(o=>o).ToList() ;

注意:

    Linq 與Lambda表達式取出的結果有所不一樣.Linq取出的結果的記錄數與Sql中的Left Join的結果相同,而Lambda表達式取出的記錄數是sgroup表中的記錄數,sgroupuser對應的記錄是以對象集合存在於結果中

附:

下面是Inner Join:

Linq語法以下:

var sg = (from g in dc.sgroup
                    join gu in dc.sgroupuser on g.gKey equals gu.gKey                  
                    select new { g, gu }).ToList();

Lambda表達式以下：

var sg = dc.sgroup.Join(dc.sgroupuser, g => g.gKey, gu => gu.gKey, (g, gu) => new { g, gu }).Select(o=>o).ToList() ;

注意:

   上面最後都用到了ToList()方法 , 用ToList()是爲了一次性將數據取到本地.

 

        private string GetSecSolicitImplementCount(DataSet aTmpDs1, DataSet aTmpDs2, int aMonth)
        {
            DataTable dt1 = aTmpDs1.Tables[0];
            DataTable dt2 = aTmpDs2.Tables[0];

            //使用LINQ計算二次招攬任務實施數
            var query = from row1 in dt1.AsEnumerable()
                join row2 in dt2.AsEnumerable() on row1.Field<string>("TASKID") equals row2.Field<string>("TASKID") 
                    into l
                from lgu in l.DefaultIfEmpty()
                where row1.Field<DateTime>("NEXTSTEPTIME1").Month == aMonth &&
                     (lgu == null ||
                     row1.Field<DateTime>("NEXTSTEPTIME1") <= lgu.Field<DateTime>("DELIVEREDDATE") )
                select new
                {
                    TaskID = row1.Field<string>("TASKID"),
                    lgu
                };
                

            var secSolicitImplementCount = query.ToArray().Count();


            return secSolicitImplementCount.ToString();

        }