Question

我有下面的linq声明。如何在没有循环的情况下解决这个问题。它是一个标签系统，我只想要那些带有“myint”中带有ID的标签的练习

int[] myints = {1,2};
  foreach (int tagid_temp in myints)
  {
    ExerciseByTagId = 
        (from exercise in context.ExerciseSet
         where context.ItemsTagsSet
               .Where(a => a.TagsId == tagid_temp)
               .Select(a => a.ExerciseId).Contains(exercise.Id)
      select exercise);
  }

Answer 1

根据您的查询猜测一下，但是这样的话？

（编辑 - 意识到如果找到多个匹配的代码，我的第一个示例会返回重复的练习）

<击> int [] myints = {1,2};

ExerciseByTagId = context.ExerciseSet .Where(e => context.ItemsTags .Any(t=> t.ExerciseId == e.Id && myints.Contains(t.TagsId) );

<击>

获取列表中所有相关项目的项目：

int[] myints = new int[] {1,2}; var ExerciseByTagId = context.ExerciseSet .Where( e => context.ItemsTags .Where(t=> t.ExerciseId == e.Id) .All(t => myints.Contains(t.TagsId)) );

Answer 2

Contains()非常接近您的需求，因此请使用您自己的ContainsAll()函数：

public static bool ContainsAll<T>(this IEnumerable<T> sequence, params T[] matches)
{
    return matches.All(value => sequence.Contains(value));
}

Answer 3

我在一个相当类似的db结构上测试了它，它产生了一个SQL语句：

var selected = new [] {1,2};

var ex = from ts in context.ItemsTagsSet
         where selected.Contains(ts.TagsId)
         group ts by ts.ExerciseId into g select new
         {
            ExerciseId = g.Key,
            Count      = g.Count()
         } into x
         where x.Count == selected.Length
         join e in context.ExerciseSet on e.ExerciseId equals x.ExerciseId 
         select e;

优化linq语句

3 个答案: