Refactor code structure for improved readability and maintainability

app/models/playlist.py

@@ -0,0 +1,26 @@
+from typing import TYPE_CHECKING
+
+from sqlmodel import Field, Relationship
+
+from app.models.base import BaseModel
+
+if TYPE_CHECKING:
+    from app.models.playlist_sound import PlaylistSound
+    from app.models.user import User
+
+
+class Playlist(BaseModel, table=True):
+    """Database model for a playlist."""
+
+    user_id: int | None = Field(foreign_key="user.id", default=None)
+    name: str = Field(unique=True, nullable=False)
+    description: str | None = Field(default=None)
+    genre: str | None = Field(default=None)
+    is_main: bool = Field(default=False, nullable=False)
+    is_current: bool = Field(default=False, nullable=False)
+    is_deletable: bool = Field(default=True, nullable=False)
+
+
+    # relationships
+    user: "User" = Relationship(back_populates="playlists")
+    playlist_sounds: list["PlaylistSound"] = Relationship(back_populates="playlist")