Dynamically building LINQ query to search objects

[NickThissen]

Hi,

I am creating a mediaplayer / playlist creator tool that basically imports MP3 songs into playlists (grids). I'm looking to add search functionality where the user can search all open playlists (or a subset of the open playlists). A Playlist is basically a collection of AudioFiles, where an AudioFile is a class that holds the filename of the MP3 file and then exposes the tags (Title, Artist, Album, etc) in public properties.

The idea is that the user can search for a certain expression (for example "the"), and that he can then choose whether to search in the title, in the title and artist, in the title or artist, in the title, artist and/or album, etc. However, I'm having a hard time implementing this and also having it kind of dynamic.

At the moment I am simply gathering all the AudioFiles from the open playlists (or from the subset of playlists the user chooses) and then running a simple LINQ query to find those AudioFiles where the Title contains the search text. Then I display the resulting AudioFiles in a new playlist window:

If Not String.IsNullOrWhiteSpace(searchText.Text) Then
            Dim files As New List(Of AudioFile)
 
            ' Gather all the AudioFiles from the relevant windows
            For Each playlistWindow In _MainWindow.PlaylistWindows
                files.AddRange(playlistWindow.Playlist)
            Next
 
            ' Extract those where the Title contains the search text
            Dim matchingFiles = From f In files
                                Where f.Title.Contains(searchText.Text)
                                Select f
 
            Me.OpenPlaylist(matchingFiles)
        End If

Obviously this works only for querying the title, albums and artists aren't used at all. Also, there are no options like case sensitivity, whole word searching, etc.

I need to extend this to include these options as well as include searching albums and artists optionally. The user should be able to choose the combination of tags he wants to look in. So for example he could choose Title AND Album (in which case only songs where the search text is in the Title AND in the Album will be returned), he could choose Artist OR Album (returning songs where the searchtext is in the artist OR in the album (or both)), etc.

I am having a hard time implementing this... Of course I could just write a query for every possible combination, but that will get cumbersome very fast, not to mention that it would be very hard to extend later should I want to add more tags the user can search in.

So basically I am looking for a way to dynamically run a query like this, keeping into account that the user might want to look for Titles and Albums only, not for Artists, etc.
Besides that I'm also not really sure how the UI should look either. At the moment I just have three Checkboxes, one for Title, Artist and Album. But how do I let the user distinguish between Titles AND Artists or Titles OR Artists..?

Thanks for any help!


EDIT
In case the AND / OR distinguishing is too hard, I would be happy to start with just letting it default to 'OR', so that the user can check Title and Album for example. If he would then search for 'a' then all songs that contain 'a' in their title as well as all songs that contain 'a' in their album should be returned. I guess that makes it easier, but I still wouldn't know how to dynamically create the LINQ query.

[jmcilhinney]

You can compose LINQ queries using function syntax, e.g.

If someCondition Then
    query = query.Where(predicate1)
Else
    query = query.Where(predicate2)
End If

You can append multiple Where calls if desired but note that the predicates will be ANDed together. As far as I'm aware, there's no way to OR multiple predicates. Conditions being ORed must be used within the same Where call.

[NickThissen]

Yeah, the AND is the problem here. By default it needs to be OR, and maybe later I'll try to implement AND as well as an option.

At the moment I have gotten the OR to work though, using this:

Dim matchingFiles = From f In files _
                                Where Me.SearchTag(f.Title, searchTitlesCheckbox) _
                                OrElse Me.SearchTag(f.Artist, searchArtistsCheckbox) _
                                OrElse Me.SearchTag(f.Album, searchAlbumsCheckbox)
                                Select f

and the SearchTag function returns the 'Contains' method if the corresponding checkbox is checked, or it returns False if it's not:

Private Function SearchTag(ByVal tag As String, ByVal checkBox As CheckBox) As Boolean
        If checkBox.IsChecked Then
            Dim sourceText, targetText As String
            If caseSensitiveCheckbox.IsChecked Then
                sourceText = tag
                targetText = searchText.Text.Trim()
            Else
                sourceText = tag.ToLower()
                targetText = searchText.Text.Trim().ToLower()
            End If
            Return sourceText.Contains(targetText)
        Else
            Return False
        End If
    End Function

This is easy enough to extend should I want to add more searchable tags (I'd just add more parts to the Where query), but I still don't see any way to let the user choose whether he wants OR or AND...