Category rendering, DB columns refined.

services/categories.py

@@ -0,0 +1,18 @@
+from typing import Optional
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from dto.categories import CategoryDTO
+from repositories import CategoriesRepository
+
+
+class CategoryService:
+    def __init__(self, category_repo: CategoriesRepository):
+        self.category_repo = category_repo
+
+    async def get_children(
+        self, session: AsyncSession, parent_id: Optional[int] = None
+    ) -> list[CategoryDTO]:
+        result = await self.category_repo.get_category_by_parent_id(session, parent_id)
+        return [
+            CategoryDTO(x.id, x.name) for x in result
+        ]  # FIXME: Optimization may be required here - O(n)