LINQ to SQL 中的堆栈溢出异常

Question

我有一种方法，该方法基于某些参数在给定字符串列表的两个日期之间查找“交易”。当列表 > 1000 时，我在尝试迭代列表时遇到堆栈溢出异常。

这是我的代码

public List<string> CodesWithTransactionsBetweenDates(DateTime startInclusive, DateTime endExclusive, List<string> associatedCodes, int marketId)
    {
        List<string> codesWithTransactionsInPeriod = new List<string>();
        using (var context = new MarketPlaceEntities())
        {
            var transactionList = (from transactions in context.Transactions
                                   where
                                    associatedCodes.Contains(transactions.User.Code) &&
                                    transactions.MarketId == marketId &&
                                    transactions.Date >= startInclusive &&
                                    transactions.Date < endExclusive
                                   group transactions by transactions.User.Code into uniqueIds
                                   select new { UserCode = uniqueIds.Key });
            foreach (var transaction in transactionList)
            {
                codesWithTransactionsInPeriod.Add(transaction.UserCode);
            }
            return codesWithTransactionsInPeriod;
        }
    }

这是堆栈跟踪......它超过了visual studio可以处理的点。

System.Data.Entity.dll!System.Data.Query.InternalTrees.BasicOpVisitor.VisitChildren(System.Data.Query.InternalTrees.Node n) + 0x3 bytes 
System.Data.Entity.dll!System.Data.Query.PlanCompiler.GroupAggregateRefComputingVisitor.VisitDefault(System.Data.Query.InternalTrees.Node n) + 0x2b bytes   
System.Data.Entity.dll!System.Data.Query.InternalTrees.BasicOpVisitor.VisitRelOpDefault(System.Data.Query.InternalTrees.RelOp op, System.Data.Query.InternalTrees.Node n) + 0xe bytes   
System.Data.Entity.dll!System.Data.Query.InternalTrees.BasicOpVisitor.VisitApplyOp(System.Data.Query.InternalTrees.ApplyBaseOp op, System.Data.Query.InternalTrees.Node n) + 0xe bytes  
System.Data.Entity.dll!System.Data.Query.InternalTrees.BasicOpVisitor.Visit(System.Data.Query.InternalTrees.OuterApplyOp op, System.Data.Query.InternalTrees.Node n) + 0xe bytes    
System.Data.Entity.dll!System.Data.Query.InternalTrees.OuterApplyOp.Accept(System.Data.Query.InternalTrees.BasicOpVisitor v, System.Data.Query.InternalTrees.Node n) + 0x10 bytes   
System.Data.Entity.dll!System.Data.Query.InternalTrees.BasicOpVisitor.VisitNode(System.Data.Query.InternalTrees.Node n) + 0x14 bytes    
System.Data.Entity.dll!System.Data.Query.InternalTrees.BasicOpVisitor.VisitChildren(System.Data.Query.InternalTrees.Node n) + 0x60 bytes    

我的问题是有什么方法可以处理这个查询，这样我就不必担心堆栈溢出异常？

Answer 1

这里有两个大问题 - 对于每个唯一的 id 键，您正在内存中创建具有单个属性的新对象。此外，您还有无用的本地列表，您可以在其中复制所有这些对象。每次列表容量填满时，都会创建新的内部数组并将所有对象复制到那里。

您可以通过 IEnumerable 使用流处理。在这种情况下，您不需要将所有数据保存在内存中：

public IEnumerable<string> CodesWithTransactionsBetweenDates(
         DateTime startInclusive, DateTime endExclusive, 
         List<string> associatedCodes, int marketId)
{
    // do not use local list

    using (var context = new MarketPlaceEntities())
    {
        return from transactions in context.Transactions
                where associatedCodes.Contains(transactions.User.Code) &&
                      transactions.MarketId == marketId &&
                      transactions.Date >= startInclusive &&
                      transactions.Date < endExclusive
                      group transactions by transactions.User.Code into uniqueIds
                      select uniqueIds.Key; // do not create anonymous object
    }
}

If you need list, you can apply ToList() on this query. But you definitely don't need create anonymous objects and copy them to local list.