Linq To Sql中实现Left Join与Inner Join使用Linq语法与lambda表达式
当前有两个表,sgroup与sgroupuser,两者通过gKey关联,而sgroup表记录的是组,而sgroupuser记录是组中的用户,因此在sgroupuser中不一定有数据。需要使用Left Join获取数据:
Linq语法如下:
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表达式如下:
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 与Lambda表达式取出的结果有所不同.Linq取出的结果的记录数与Sql中的Left Join的结果相同,而Lambda表达式取出的记录数是sgroup表中的记录数,sgroupuser对应的记录是以对象集合存在于结果中
附:
下面是Inner Join:
Linq语法如下:
var sg = (from g in dc.sgroup
join gu in dc.sgroupuser on g.gKey equals gu.gKey
select new { g, gu }).ToList();
Lambda表达式如下:
var sg = dc.sgroup.Join(dc.sgroupuser, g => g.gKey, gu => gu.gKey, (g, gu) => new { g, gu }).Select(o=>o).ToList() ;
注意:
上面最后都用到了ToList()方法 , 用ToList()是为了一次性将数据取到本地.
private string GetSecSolicitImplementCount(DataSet aTmpDs1, DataSet aTmpDs2, int aMonth) { DataTable dt1 = aTmpDs1.Tables[0]; DataTable dt2 = aTmpDs2.Tables[0]; //使用LINQ计算二次招揽任务实施数 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(); }