Update database architecture. Add genres and actors

database/models/audiobook_genres.py

@@ -0,0 +1,25 @@
+from sqlalchemy import Column, Integer, ForeignKey, PrimaryKeyConstraint, String
+from sqlalchemy.orm import relationship
+
+from ..database import Base
+
+
+class AudiobookGenre(Base):
+    __tablename__ = "audiobook_genres"
+
+    id = Column(Integer, primary_key=True)
+    genre = Column(String, nullable=False, unique=True)
+
+    audiobooks = relationship("Audiobook", secondary="audiobook_to_genre",
+                              lazy="selectin")
+
+
+class AudiobookToGenre(Base):
+    __tablename__ = "audiobook_to_genre"
+    __table_args__ = (
+        PrimaryKeyConstraint("audiobook_id", "genre_id"),
+    )
+
+    audiobook_id = Column(Integer, ForeignKey("audiobooks.id"), nullable=False)
+    genre_id = Column(Integer, ForeignKey(
+        "audiobook_genres.id"), nullable=False)