c# - 如何将此 SQL 转换为 Linq？

Question

我有一个查询：

select siniflar.id,siniflar.sinif,count(ogrenciId) 
  from siniflar
  left join oda
  on siniflar.id=oda.sinifId
  where siniflar.ogretmenid=2
  group by siniflar.id,siniflar.sinif

这是我对 Linq 的转换：

  from snf in db.siniflar
     join oda in db.oda
     on snf.id equals oda.sinifId
     where snf.ogretmenid==oID
     group oda by new
     {
     snf.id,snf.sinif
     } into g 
     select new
     {
     sinifIDsi=g.Key.id,
     sinifADi=g.Key.sinif,
     Column1 = g.Count()
     })

我也想要空计数的结果，但我无法将左或右加入与 group by 一起适应 linq。DefaultIfEmpty() 方法不起作用。谁能帮我？

Answer 1

您还可以添加DefaultIfEmpty()计算左表的空计数，如以下查询：

var result = (from snf in db.siniflar
             join oda in db.oda on snf.id equals oda.sinifId into leftedOdatas
             from leftedOdata in leftedOdatas.DefaultIfEmpty()
             where snf.ogretmenid == 2
             group leftedOdata by new {snf.id, snf.sinif } into g 
             select new
             {
                 sinifIDsi = g.Key.id,
                 sinifADi = g.Key.sinif,
                 Column1 = g.Count(x => x?.sinifId != null)
             }).ToList();

我希望你觉得这有帮助。