LINQ如何实现多表关联查询

[Hunk_sz]

sql语句：select S.ITEM_CODE,B.BAR_CODE,S.SIZEGROUPID,R.SIZECODE,R.SIZENAME from stock s
inner join barcodes b on b.item_code = s.item_code
left join sizeratio r on r.sizegroupid = s.sizegroupid and r.sizeid = b.sizeid where s.bran_code ='MF';我在dataset中分别用dtStock,dtBarcodes,dtSizeRatio存放stock,barcodes,sizeratio表中的数据，请问用LINQ如何实现像sql查询一样的结果？
我在数据库中查询是有结果的，可是用下面这个语句就没有结果了，请各位高手给指点一下。谢谢！
var querySize = from s in dtStock.AsEnumerable()
let size = from b in dtBarcodes.AsEnumerable()
join sr in dtSizeRatio.AsEnumerable()
on b.Field<decimal>("sizeid") equals sr.Field<decimal>("sizeid") select new
{
item = b["item_code"],
bar = b["bar_code"],
sizegroup_id = sr["sizegroupid"],
size_id = sr["sizeid"],
size_code = sr["sizecode"],
size_name = sr["sizename"]
}
where s["item_code"] == size.First().item && s["sizegroupid"] == size.First().sizegroup_id && s["bran_code"] == "MF"
select new
{
itemcode = s["item_code"],
barcode = size.First().bar,
sizegroupid = size.First().sizegroup_id,
sizecode = size.First().size_code,
sizename = size.First().size_name
};

[q107770540]

var querySize = from s in dtStock.AsEnumerable().Where(x=>x.Field<string>("bran_code")=="MF")
  join b in dtBarcodes.AsEnumerable()
  on b.Field<int>("item_code") equals s.b.Field<int>("item_code")
  join r in dtSizeRatio.AsEnumerable()
  on new {sizegroupid=r.Field<decimal>("sizeid") ,sizeid=r.Field<decimal>("sizeid") } equals  new {sizegroupid=s.Field<decimal>("sizeid") ,sizeid=b.Field<decimal>("sizeid")} into leftJoin
  from sr in leftJoin.DefalutIfEmpty()
 select new
  {
  item = b["item_code"],
  bar = b["bar_code"],
  sizegroup_id =sr==null?0: sr["sizegroupid"],
  size_id = sr==null?0: sr["sizeid"],
  size_code = sr==null?0: sr["sizecode"],
  size_name = sr==null?0: sr["sizename"]
  };

[你的选择H]

上面的好像有些问题，更改一下：
var querySize = from s in dtStock.AsEnumerable().Where(x => x.Field<string>("bran_code") == "MF")
join b in dtBarcodes.AsEnumerable()
on s.Field<int>("item_code") equals b.Field<int>("item_code")
join r in dtSizeRatio.AsEnumerable()
on new { sizegroupid = s.Field<decimal>("sizeid"), sizeid = b.Field<decimal>("sizeid") } equals new { sizegroupid = r.Field<decimal>("sizeid"), sizeid = r.Field<decimal>("sizeid") } into leftJoin
from sr in leftJoin.DefalutIfEmpty()
select new
{
item = b["item_code"],
bar = b["bar_code"],
sizegroup_id = sr == null ? 0 : sr["sizegroupid"],
size_id = sr == null ? 0 : sr["sizeid"],
size_code = sr == null ? 0 : sr["sizecode"],
size_name = sr == null ? 0 : sr["sizename"]
};

[Hunk_sz]

谢谢q107770540的帮忙，很是奇怪，你给出的语句执行查询同样是没有结果的

[Astpiy]

建议你使用“Linqer.exe”，这个工具可以将SQL转换为Linq to Sql