Linq 按标签列表过滤帖子

Question

public class LogItemTag
{
    public int ID { get; set; }
    public string Tagname { get; set; }
}

var logItemTags = new List<LogItemTag>();
logItemTags.Add(new LogItemTag { ID = 1, TagName = "red" });
logItemTags.Add(new LogItemTag { ID = 1, TagName = "green" });
logItemTags.Add(new LogItemTag { ID = 3, TagName = "blue" });
logItemTags.Add(new LogItemTag { ID = 3, TagName = "red" });
logItemTags.Add(new LogItemTag { ID = 4, TagName = "green" });
logItemTags.Add(new LogItemTag { ID = 6, TagName = "white" });
logItemTags.Add(new LogItemTag { ID = 7, TagName = "red" });
logItemTags.Add(new LogItemTag { ID = 7, TagName = "green" });

var listOfTagsToFilterOn = new List<string> {"red", "green" };

//I need a list of ids 1 and 7 only.

//this query produces 6 ids - 1,1,3,4,7,7
var query = logItemTags.Where(lit => listOfTagsToFilterOn.Contains(lit.TagName)).Select(lit => lit.ID).ToList();

Answer 1

使用Contains扩展方法:

var tags=new List<string>(){"red", "green"};// the collection of tags you want to get the ids
var query=LogItemTagList.Where(l=>tags.Contains(l.Tagname)).Select(l=>l.ID);

更新 1

我认为这就是您想要实现的目标:

var query=LogItemTagList.Where(l=>tags.Contains(l.Tagname))
                        .GroupBy(l=>l.ID)
                        .Where(g=>g.Count==tags.Count)
                        .Select(g=>g.Key)
                        .ToList();