c#-4.0 - 性能问题：如何一次执行两个 lambda 表达式？使用“包含”和“任何”运算符

Question

示例代码

var Ids = _db.Projects.Where(Project=>Project.Title!="test23rdoct")
    .Select (pro => pro.Id);

Expression<Func<Company, bool>> masterExpression = 
    Company => Company.Participants.Any(part => ids.Contains(part.Project.Id));

IQueryable<Object> queryEntity = _db.Companies.Where(masterExpression)

上述查询执行两次。在服务器中存储 id（有时 id 超过 50k 个）。它会导致性能问题。有人可以建议如何组合这两个查询并立即执行吗？

Answer 1

怎么样：

var queryEntity = _db.Companies.Where(c => c.Partipants.Any(p => p.Project.Title != "test23rdoct"));

编辑：使用复杂的查询，您还可以拆分：

Func<Project, bool> projectFilter = Project => ((Compare(Convert(Project.Title), "a") > 0) AndAlso ((Convert(Project.Title) != "test23rdoct") AndAlso
(Project.Participants.Any(Participant => (Compare(Convert(Participant.ParticipantRole.Name), "Finance") > 0)) AndAlso 
(Project.Participants.Any(Participant => (Convert(Participant.Person.FirstName) != "test1")) AndAlso 
Project.Participants.Any(Participant => (Compare(Convert(Participant.Company.Name), "test") > 0))))));

然后做：

var queryEntity = _db.Companies.Where(c => c.Partipants.Any(p => projectFilter(p.Project));

Answer 2

这样的使用Join是否适合您的需求？

Expression<Func<Company, bool>> masterExpression = 
    Company => Company.Participants.Join (Ids, p => p.Project.ID, id => id, (p, id) => p).Any();
IQueryable<Object> queryEntity = _db.Companies.Where(masterExpression);

Answer 3

我得到了避免两次执行 Lambda 的解决方案。为此，我使用了这些扩展方法 Invoke() 和 AsExpandable()。它在 Linqkit dll 中可用。

Expression<Func<Company, bool>> masterExpression = Company => Company.Participants.Any(part => masterLamba.Invoke(part.Project));
queryEntity = _db.Companies.AsExpandable().Where(masterExpression);