LINQ查询使用ALL

Question

想象一下照片标签系统......

    public class Photo
    {
      public IList<Tag> Tags {get;set;}
    }

    public class Tag
    {
      public string Name {get;set;}
    }

IList<Tag> tags = new [] {
                             new Tag{Name = "tag1"}, 
                             new Tag{Name = "tag2"}
                         };

IList<Photo> photos = GetAllPhotos();

这一行:

var results = //return photos when Photo.Tags contains BOTH tags

我可以使用LINQ运算符来实现这一目标吗？

Answer 1

当然:

// All the tags in "tags" are contained in p.Tags
var results = photos.Where(p => tags.All(tag => p.Tags.Contains(tag)));

要么

// All the "tags" except the ones in p.Tags ends up as an empty set
var results = photos.Where(p => !tags.Except(p.Tags).Any());

编辑:请注意,这假设实际上你在Tag上有一个适当的相等实现.否则你需要这样的东西:

var results = photos.Where(p => !tags.Select(t => t.Name)
                                     .Except(p.Tags.Select(t => t.Name)).Any());