c# - 如何改进这个 LINQ TO SQL 的可查询性？

Question

我有一个学生列表，我想在其中创建一个查询，其中获取所有项目，而不是 1 x 1，因为我在下面显示代码：

            IEnumerable<Student> = ...
            List<AnsweredTest> ats = new List<AnsweredTest>();

            foreach (var s in students)
            {
                query = from at in Database.Current.AnsweredTests
                        where at.StudentId == s.StudentId
                        select at;

                ats.Add(query.Single());
            }

            listView.ItemsSource = ats;

这对性能不利。我希望让自己清楚，如果没有，请告诉我。

Answer 1

要么加入：

   query = from at in Database.Current.AnsweredTests 
    join s in Database.Current.Students on at.StudentId == s.StudentId
    where s... // filter s if needed.
    select at;

或者获取学生 ID 列表并将其传递到查询中：

   int[] studentIds = students.Select(s => s.StudentId).ToArray();
   query = from at in Database.Current.AnsweredTests
     where studentIds.Any(id => at.StudentId == id)
     select at;

Answer 2

var ats = Database.Current.AnsweredTests
    .Where(at => students.Any(s => s.StudentId == at.StudentId).ToList()

Answer 3

也许是这样的：

var studentIds = students.Select(s => s.StudentId);
var ats = Database.Current.AnsweredTests.Where(at => studentIds.Contains(at.StudentId));