如何调试EF 5 null引用异常？

Question

当我过滤EF时，我得到一个空引用异常，但我绝对无能为力。

public IEnumerable<TonalityBatchModel> GetTonalityBatch(int briefID)
{
    try
    {
        var brief = NeptuneUnitOfWork.Briefs.FindWhere(b => b.ID == briefID).FirstOrDefault();

        if (brief != null && brief.TonalityCriteria != null)
                    {
                        return brief.TonalityCriteria.TonalityBatches
                                    .Select(b => new TonalityBatchModel()
                                        {
                                            BriefID = b.BriefID,
                                            Status = b.TonalityCriteria.IsActive == true ?"Active":"Ended",
                                            BatchID = b.ID,
                                            CompetitorID = b.BriefCompetitorID,
                                            Competitor = brief.BriefCompetitors.Where(i=>i.ID == b.BriefCompetitorID).Select(c=>c.Organisation.Name).First(),
                                            Size = b.BatchSize,
                                            StartDate = b.StartDate,
                                            EndDate = b.EndDate,
                                            IsPublished = b.Lookup_TonalityBatchStatus.ID == (int)TonalityBatchStatus.Published?"Yes":"No",
                                            IsCompleted = b.Lookup_TonalityBatchStatus.ID == (int)TonalityBatchStatus.Completed ? "Yes" : "No",
                                            IsAssigned = b.Lookup_TonalityBatchStatus.ID == (int)TonalityBatchStatus.Allocated ? "Yes" : "No",
                                            ImportantCount = b.TonalityItems.Count(i=> i.IsImportant),
                                            ArticlesCount = b.TonalityItems.Count,
                                            FavourableCount = b.TonalityItems.Count(i => i.Lookup_TonalityScoreTypes.ID ==(int)TonalitySourceType.Favourable),
                                            UnfavourableCount = b.TonalityItems.Count(i => i.Lookup_TonalityScoreTypes.ID ==(int)TonalitySourceType.Unfavourable),
                                            NeutralCount = b.TonalityItems.Count(i => i.Lookup_TonalityScoreTypes.ID ==(int)TonalitySourceType.Neutral)

                                        }).ToList();
                    }

                    return new List<TonalityBatchModel>();

            }
            catch (Exception ex)
            {
                Logger.Error(ex);
                throw;
            }
        }

Answer 1

您需要将查询缩减为更简单的查询，然后重新开始重新构建，直到NullReferenceException发生。看看你的代码，这里有一些可能的地方（我做了一些假设，因为我不知道你的模型的所有内容）：

Competitor = brief.BriefCompetitors.Where(i=>i.ID == b.BriefCompetitorID).Select(c=>c.Organisation.Name).First()

BriefCompetitors可能为null。 c.Organisation可能为空。

IsPublished = b.Lookup_TonalityBatchStatus.ID == (int)TonalityBatchStatus.Published?"Yes":"No",

（和其他类似的行）b.Lookup_TonalityBatchStatus可能为空。

ImportantCount = b.TonalityItems.Count(i=> i.IsImportant),

（和其他类似的行）b.TonalityItems可能为空。

Answer 2

我相信这是因为你的计数正在返回空记录。我可能错了，但是这里生成的SQL就像是：

INNER JOIN TonalityItems i on i.Lookup_TonalityScoreTypes == x

其中x是(int)TonalitySourceType.Favourable的值。由于此联接没有匹配的结果，因此无法执行count。您可以尝试将?? 0添加到查询的末尾：

FavourableCount = b.TonalityItems.Count(i => i.Lookup_TonalityScoreTypes.ID ==(int)TonalitySourceType.Favourable) ?? 0,