如何使用 LINQ 和 PredicateBuilder 使用子类构建谓词？

Question

我正在尝试使用此答案将 OR 运算符动态添加到 LINQ 中的 WHERE 子句：https://stackoverflow.com/a/782350/1316683

var searchPredicate = PredicateBuilder.False<Songs>();

foreach(string str in strArray)
{
    var closureVariable = str;
    searchPredicate = 
     searchPredicate.Or(SongsVar => SongsVar.Tags.Contains(closureVariable));
}

var allSongMatches = db.Songs.Where(searchPredicate);

在我的情况下，标签是一个列表，而不是一个属性，我想做这样的事情：

searchPredicate.Or(SongsVar => SongsVar.Tags.Any().TagName.Contains(closureVariable));

然后我想到了这样的东西，它不起作用：

searchPredicate.Or(x => x.Tags.Where(p => p.TagName.Contains(closureVariable )).Count() > 0);

这可能吗？

Answer 1

是的，应该可以的：

  var searchPredicate = PredicateBuilder.False<Songs>();

  var strArray = new[] {"aa", "bb"};

  foreach (string str in strArray) {
    var closureVariable = str;
    searchPredicate =
     searchPredicate.Or(songsVar => songsVar.Tags.Any(tagVar => tagVar.TagName == closureVariable));
  }

  var songs = new List<Songs> {
    new Songs {Tags = new List<Tag> {new Tag {TagName = "aa"}}},
    new Songs {Tags = new List<Tag> {new Tag {TagName = "bb"}}},
    new Songs {Tags = new List<Tag> {new Tag {TagName = "aa"}, new Tag {TagName = "cc"}}},
    new Songs {Tags = new List<Tag> {new Tag {TagName = "cc"}, new Tag {TagName = "dd"}}}
  };

  var res = songs.Where(searchPredicate.Compile());

将Songs 和Tag 定义为：

  public class Songs {
    public List<Tag> Tags { get; set; }
  }

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

然后，res 包含 songs 中定义的前 3 条记录，如预期的那样。