如何使用LINQ和PredicateBuilder使用子类构建谓词？

Question

I am trying to use this answer to dynamically add an OR operator to the WHERE clause in LINQ: 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);

In my case Tags is a List<Tag>, not a property, I would like to do something like this:

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

Then I thought of something like this, which doesn't work:

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

Is this possible?

Answer 1

Yes, it should be possible:

  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());

With Songs and Tag defined as:

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

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

Then, res contains the first 3 records defined in songs as expected.