Question

我使用ID过滤实体，但如果ID为null，那么我想返回所有实体。所以在下面的代码中，如果competitorID为null id，则返回所有简短的竞争对手。

var competitors =
                NeptuneUnitOfWork.Briefs.FindWhere(b => b.ID == briefID)
                                 .Select(b => b.BriefCompetitors.Where(b=>b.ID == competitorID)).ToList();

Answer 1

通常你会这样做：

IQueryable<Brief> briefs = NeptuneUnitOfWork.Briefs.Where(b => b.ID == briefID);

if (competitorID != null)
{
    competitors = briefs.Select(b => b.BriefCompetitors.Where(b=>b.ID == competitorID));
}
else
{
    competitors = briefs.Select(b => b.BriefCompetitors);
}

从技术上讲，您可以将问题留给SQL Server：

// Note the || clause
competitors = briefs.Where(b => b.ID == briefID)
                    .Select(b => b.BriefCompetitors.Where(b=>b.ID == competitorID || competitorID == null));

Answer 2

只是对@xanatos帖子的一个小改动

// Note the || clause
competitors = briefs.Where(b => b.ID == briefID && (competitorID == null || b.ID == competitorID));

linq to entities如果filter参数为null则选择所有实体？

2 个答案: