c# – LINQ外连接有重复

我在LINQPad中运行此查询.它的工作原理除了ProductSeries有重复的记录.

var query = from etaRecord in EtaRecord_0140

  join productSeriesRecord in ProductSeries
  on etaRecord.ProductSeriesID equals productSeriesRecord.ProductSeriesID
  into productSeriesGroup
  from productSeries in productSeriesGroup.DefaultIfEmpty()

  where etaRecord.State == "A"
  select new { EtaRecord = etaRecord,ProductSeriesRecord = productSeries };

query.Dump();

我尝试使用FirstOrDefault()而不是DefaultIfEmpty(),但我收到此错误：

An expression of type ‘LINQPad.User.ProductSeries’ is not allowed in a
subsequent from clause in a query expression with source type
‘System.Linq.IQueryable’. Type inference Failed in
the call to ‘SelectMany’.

如何获取ProductSeries的FirstOrDefault(),以便每个EtaRecord只有一行？

.NET小提琴就在这里：https://dotnetfiddle.net/kRrold

解决方法

看起来你需要分组：

var query = from etaRecord in EtaRecord_0140

join productSeriesRecord in ProductSeries
on etaRecord.ProductSeriesID equals productSeriesRecord.ProductSeriesID
into productSeriesGroup
from productSeries in productSeriesGroup.DefaultIfEmpty()

where etaRecord.State == "A"
group productSeries by new { etaRecord.ProductSeriesId,etaRecord } into g
select new 
       { 
         EtaRecord = g.Key.etaRecord,ProductSeriesRecord = g.Select(x => x).FirstOrDefault() 
        };

UPDATED FIDDLE