LINQ查询帮助 [英] LINQ Query Help

问题描述

我有这个疑问它运行联接的书籍，TradingDesks和ProductInfos。该数据是巨大的每本收集的。

I have this query which runs a join on Books, TradingDesks and ProductInfos. The data is huge in each of this collection.

var queryJoin = from b in books.Values
                                    join d in tradingDesks.Values
                                        on b.TradingDeskId equals d.Id
                                    join p in ProductInfos.Values
                                        **on b.Id equals p.RiskBookId** 
                                    select new { p, Book = b.Name, TradingDeskName = d.Name };

在突出显示的行（上b.Id等于p.RiskBookId），我也想加入喜欢，（上的b其他条件。 ID等于p.RiskBookId || p.RiskBookId == 0）。如何在这LINQ语法做到这一点。

In the highlighted line (on b.Id equals p.RiskBookId), I also want to add another condition like, (on b.Id equals p.RiskBookId || p.RiskBookId == 0) . How do I do this in this linq syntax.

我想查询像这样

var queryJoin = from b in books.Values
                from d in tradingDesks.Values.Where(x => x.Id == b.TradingDeskId)
                from p in cachedProductInfos.Values.Where(y => y.RiskBookId == b.Id)
                select new { p, Book = b.Name, TradingDeskName = d.Name };

但是，在这种情况下，查询将永远运行下去，我耗尽内存。所以我想取景它以这种方式做一些疯狂：（

But in this case, the query runs forever and I run out of memory. So I guess framing it in this fashion does something crazy :(

任何帮助是AP preciated。

Any help is appreciated.

谢谢 玛尼

推荐答案

在原来的查询，这些电话以Enumerable.Join使用幕后一个哈希表，使事情很快。如果切换到。凡，你没有得到这些哈希的好处。您可以使用明确散列来获得同样的效果。

In the original query, those calls to Enumerable.Join are using a hashtable behind the scenes to make things fast. If you switch to .Where, you don't get those hash benefits. You can use hashing explicitly to get the same effect.

ILookup<int, string> deskNameLookup = tradingDesks.Values
  .ToLookup(
    d => d.Id,
    d => d.Name
  );

ILookup<int, ProductInfo> infoLookup = ProductInfos.Values
  .ToLookup(p.RiskBookId);

foreach(b in books.Values)
{
  foreach(dName in deskNameLookup[b.TradingDeskId])
  {
    foreach(p in infoLookup[b.Id].Concat(infoLookup[0]))
    {
      var x = new {p, Book = b.Name, TradingDeskName = dName};
    }
  }
}

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