Move MongoDB classes into a seperate db module (#62)

* move album class into mongodb dir

* inherit AlbumMethods at DB Initialization level

* move album -> db/mongodb

* move mongodb classes into separate package

server/app/db/mongodb/__init__.py

@@ -0,0 +1,80 @@
+"""
+This module creates and initiliazes a MongoDB instance. It also contains the
+`convert_one()` and `conver_many()` methods for converting MongoDB cursors to Python dicts.
+"""
+import json
+
+import pymongo
+from app.db import AlbumMethods
+from app.db import ArtistMethods
+from app.db import PlaylistMethods
+from app.db import TrackMethods
+from bson import json_util
+
+
+class Mongo:
+    """
+    The base class for all mongodb classes.
+    """
+
+    def __init__(self, database):
+        mongo_uri = pymongo.MongoClient()
+        self.db = mongo_uri[database]
+
+
+class MongoAlbums(Mongo, AlbumMethods):
+
+    def __init__(self):
+        super(MongoAlbums, self).__init__("ALICE_ALBUMS")
+        self.collection = self.db["ALL_ALBUMS"]
+
+
+class MongoArtists(Mongo, ArtistMethods):
+
+    def __init__(self):
+        super(MongoArtists, self).__init__("ALICE_ARTISTS")
+        self.collection = self.db["ALL_ARTISTS"]
+
+
+class MongoPlaylists(Mongo, PlaylistMethods):
+
+    def __init__(self):
+        super(MongoPlaylists, self).__init__("ALICE_PLAYLISTS")
+        self.collection = self.db["ALL_PLAYLISTS"]
+
+
+class MongoTracks(Mongo, TrackMethods):
+
+    def __init__(self):
+        super(MongoTracks, self).__init__("ALICE_MUSIC_TRACKS")
+        self.collection = self.db["ALL_TRACKS"]
+
+
+# ====================================================================== #
+# cursor convertion methods
+
+
+def convert_one(song):
+    """
+    Converts a single mongodb cursor to a json object.
+    """
+    json_song = json.dumps(song, default=json_util.default)
+    loaded_song = json.loads(json_song)
+
+    return loaded_song
+
+
+def convert_many(array):
+    """
+    Converts a list of mongodb cursors to a list of json objects.
+    """
+
+    songs = []
+
+    for song in array:
+        json_song = json.dumps(song, default=json_util.default)
+        loaded_song = json.loads(json_song)
+
+        songs.append(loaded_song)
+
+    return songs