Made some small code improvements

app/src/main/java/org/schabi/newpipe/database/Migrations.java

@@ -206,20 +206,16 @@ public final class Migrations {
                     + "INTEGER NOT NULL DEFAULT -1");
 
             // Migrate the thumbnail_url to the thumbnail_stream_id
-            database.execSQL("CREATE TEMPORARY TABLE temporary_table AS"
+            database.execSQL("UPDATE playlists SET thumbnail_stream_id = ("
+                    + " SELECT CASE WHEN COUNT(*) != 0 then stream_uid ELSE -1 END"
+                    + " FROM ("
                     + " SELECT p.uid AS playlist_uid, s.uid AS stream_uid"
                     + " FROM playlists p"
                     + " LEFT JOIN playlist_stream_join ps ON p.uid = ps.playlist_id"
                     + " LEFT JOIN streams s ON s.uid = ps.stream_id"
-                    + " WHERE s.thumbnail_url = p.thumbnail_url");
+                    + " WHERE s.thumbnail_url = p.thumbnail_url) AS temporary_table"
-
-            database.execSQL("UPDATE playlists SET thumbnail_stream_id = ("
-                    + "SELECT CASE WHEN COUNT(*) != 0 then stream_uid ELSE -1 END "
-                    + "FROM temporary_table "
                     + " WHERE playlist_uid = playlists.uid)");
 
-            database.execSQL("DROP TABLE temporary_table");
-
             // Remove the thumbnail_url field in the playlist table
             database.execSQL("CREATE TABLE IF NOT EXISTS `playlists_new`"
                     + "(uid INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "

app/src/main/java/org/schabi/newpipe/database/playlist/dao/PlaylistStreamDAO.java

@@ -9,6 +9,7 @@ import org.schabi.newpipe.database.BasicDAO;
 import org.schabi.newpipe.database.playlist.PlaylistDuplicatesEntry;
 import org.schabi.newpipe.database.playlist.PlaylistMetadataEntry;
 import org.schabi.newpipe.database.playlist.PlaylistStreamEntry;
+import org.schabi.newpipe.database.playlist.model.PlaylistEntity;
 import org.schabi.newpipe.database.playlist.model.PlaylistStreamEntity;
 
 import java.util.List;
@@ -59,14 +60,15 @@ public interface PlaylistStreamDAO extends BasicDAO<PlaylistStreamEntity> {
             + " WHERE " + JOIN_PLAYLIST_ID + " = :playlistId")
     Flowable<Integer> getMaximumIndexOf(long playlistId);
 
-    @Query("SELECT CASE WHEN COUNT(*) != 0 then " + STREAM_ID + " ELSE -1 END"
+    @Query("SELECT CASE WHEN COUNT(*) != 0 then " + STREAM_ID
+            + " ELSE " + PlaylistEntity.DEFAULT_THUMBNAIL_ID + " END"
             + " FROM " + STREAM_TABLE
             + " LEFT JOIN " + PLAYLIST_STREAM_JOIN_TABLE
             + " ON " + STREAM_ID + " = " + JOIN_STREAM_ID
             + " WHERE " + JOIN_PLAYLIST_ID + " = :playlistId "
             + " LIMIT 1"
     )
-    Flowable<Long> getAutomaticThumbnailUrl(long playlistId);
+    Flowable<Long> getAutomaticThumbnailStreamId(long playlistId);
 
     @RewriteQueriesToDropUnusedColumns
     @Transaction
@@ -91,14 +93,13 @@ public interface PlaylistStreamDAO extends BasicDAO<PlaylistStreamEntity> {
     @Transaction
     @Query("SELECT " + PLAYLIST_ID + ", " + PLAYLIST_NAME + ","
 
-            + " CASE WHEN " + PLAYLIST_THUMBNAIL_STREAM_ID + " = -1"
+            + " CASE WHEN " + PLAYLIST_THUMBNAIL_STREAM_ID + " = "
-            + " THEN " + "'" + DEFAULT_THUMBNAIL + "'"
+            + PlaylistEntity.DEFAULT_THUMBNAIL_ID + " THEN " + "'" + DEFAULT_THUMBNAIL + "'"
             + " ELSE (SELECT " + STREAM_THUMBNAIL_URL
             + " FROM " + STREAM_TABLE
             + " WHERE " + STREAM_TABLE + "." + STREAM_ID + " = " + PLAYLIST_THUMBNAIL_STREAM_ID
             + " ) END AS " + PLAYLIST_THUMBNAIL_URL + ", "
 
-            + PLAYLIST_NAME + ", "
             + "COALESCE(COUNT(" + JOIN_PLAYLIST_ID + "), 0) AS " + PLAYLIST_STREAM_COUNT
             + " FROM " + PLAYLIST_TABLE
             + " LEFT JOIN " + PLAYLIST_STREAM_JOIN_TABLE
@@ -111,14 +112,14 @@ public interface PlaylistStreamDAO extends BasicDAO<PlaylistStreamEntity> {
     @Query("SELECT " + PLAYLIST_TABLE + "." + PLAYLIST_ID + ", "
             + PLAYLIST_NAME + ", "
 
-            + " CASE WHEN " + PLAYLIST_THUMBNAIL_STREAM_ID + " = -1"
+            + " CASE WHEN " + PLAYLIST_THUMBNAIL_STREAM_ID + " = "
-            + " THEN " + "'" + DEFAULT_THUMBNAIL + "'"
+            + PlaylistEntity.DEFAULT_THUMBNAIL_ID + " THEN " + "'" + DEFAULT_THUMBNAIL + "'"
             + " ELSE (SELECT " + STREAM_THUMBNAIL_URL
             + " FROM " + STREAM_TABLE
             + " WHERE " + STREAM_TABLE + "." + STREAM_ID + " = " + PLAYLIST_THUMBNAIL_STREAM_ID
-            + " ) END AS " + PLAYLIST_THUMBNAIL_URL
+            + " ) END AS " + PLAYLIST_THUMBNAIL_URL + ", "
 
-            + ", COALESCE(COUNT(" + JOIN_PLAYLIST_ID + "), 0) AS " + PLAYLIST_STREAM_COUNT + ", "
+            + "COALESCE(COUNT(" + JOIN_PLAYLIST_ID + "), 0) AS " + PLAYLIST_STREAM_COUNT + ", "
             + "COALESCE(SUM(" + STREAM_URL + " = :streamUrl), 0) AS "
                 + PLAYLIST_TIMES_STREAM_IS_CONTAINED
 

app/src/main/java/org/schabi/newpipe/database/playlist/model/PlaylistEntity.java

@@ -16,6 +16,8 @@ public class PlaylistEntity {
 
     public static final String DEFAULT_THUMBNAIL = "drawable://"
             + R.drawable.placeholder_thumbnail_playlist;
+    public static final long DEFAULT_THUMBNAIL_ID = -1;
+
     public static final String PLAYLIST_TABLE = "playlists";
     public static final String PLAYLIST_ID = "uid";
     public static final String PLAYLIST_NAME = "name";

app/src/main/java/org/schabi/newpipe/local/playlist/LocalPlaylistFragment.java

@@ -35,6 +35,7 @@ import org.schabi.newpipe.R;
 import org.schabi.newpipe.database.LocalItem;
 import org.schabi.newpipe.database.history.model.StreamHistoryEntry;
 import org.schabi.newpipe.database.playlist.PlaylistStreamEntry;
+import org.schabi.newpipe.database.playlist.model.PlaylistEntity;
 import org.schabi.newpipe.database.stream.model.StreamEntity;
 import org.schabi.newpipe.databinding.DialogEditTextBinding;
 import org.schabi.newpipe.databinding.LocalPlaylistHeaderBinding;
@@ -70,8 +71,6 @@ import io.reactivex.rxjava3.schedulers.Schedulers;
 import io.reactivex.rxjava3.subjects.PublishSubject;
 
 public class LocalPlaylistFragment extends BaseLocalListFragment<List<PlaylistStreamEntry>, Void> {
-    public static final long DEFAULT_THUMBNAIL_ID = -1;
-    public static final long NO_THUMBNAIL_ID = -2;
     // Save the list 10 seconds after the last change occurred
     private static final long SAVE_DEBOUNCE_MILLIS = 10000;
     private static final int MINIMUM_INITIAL_DRAG_VELOCITY = 12;
@@ -624,7 +623,7 @@ public class LocalPlaylistFragment extends BaseLocalListFragment<List<PlaylistSt
             thumbnailStreamId = ((PlaylistStreamEntry) itemListAdapter.getItemsList().get(0))
                     .getStreamEntity().getUid();
         } else {
-            thumbnailStreamId = DEFAULT_THUMBNAIL_ID;
+            thumbnailStreamId = PlaylistEntity.DEFAULT_THUMBNAIL_ID;
         }
 
         changeThumbnailStreamId(thumbnailStreamId, false);

app/src/main/java/org/schabi/newpipe/local/playlist/LocalPlaylistManager.java

@@ -23,6 +23,8 @@ import io.reactivex.rxjava3.core.Single;
 import io.reactivex.rxjava3.schedulers.Schedulers;
 
 public class LocalPlaylistManager {
+    private static final long THUMBNAIL_ID_LEAVE_UNCHANGED = -2;
+
     private final AppDatabase database;
     private final StreamDAO streamTable;
     private final PlaylistDAO playlistTable;
@@ -115,7 +117,7 @@ public class LocalPlaylistManager {
     }
 
     public Maybe<Integer> renamePlaylist(final long playlistId, final String name) {
-        return modifyPlaylist(playlistId, name, LocalPlaylistFragment.NO_THUMBNAIL_ID, false);
+        return modifyPlaylist(playlistId, name, THUMBNAIL_ID_LEAVE_UNCHANGED, false);
     }
 
     public Maybe<Integer> changePlaylistThumbnail(final long playlistId,
@@ -134,10 +136,10 @@ public class LocalPlaylistManager {
     }
 
     public long getAutomaticPlaylistThumbnailStreamId(final long playlistId) {
-        final long streamId = playlistStreamTable.getAutomaticThumbnailUrl(playlistId)
+        final long streamId = playlistStreamTable.getAutomaticThumbnailStreamId(playlistId)
                 .blockingFirst();
         if (streamId < 0) {
-            return LocalPlaylistFragment.DEFAULT_THUMBNAIL_ID;
+            return PlaylistEntity.DEFAULT_THUMBNAIL_ID;
         }
         return streamId;
     }
@@ -154,7 +156,7 @@ public class LocalPlaylistManager {
                     if (name != null) {
                         playlist.setName(name);
                     }
-                    if (thumbnailStreamId != LocalPlaylistFragment.NO_THUMBNAIL_ID) {
+                    if (thumbnailStreamId != THUMBNAIL_ID_LEAVE_UNCHANGED) {
                         playlist.setThumbnailStreamId(thumbnailStreamId);
                         playlist.setIsThumbnailPermanent(isPermanent);
                     }