draft: category tree building

src/models/transactions.py

@@ -5,6 +5,7 @@ from pydantic import Field, computed_field
 from sqlalchemy import Date, ForeignKey, Index, Integer, String, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
+from src.models.category import Category
 from src.models.common import Amount, ExportBaseModel, IngestdbBase, date2str, hashify
 
 
@@ -29,7 +30,8 @@ class Transaction(ExportBaseModel):
     other_name: str | None = None
     other_iban: str | None = None
     # TODO: The Pydantic model should hold a category object, NOT the category id which is owned by the DB
-    category_id: int | None = None
+    category: Category | None
+    category_id: int | None = None # remove!
 
     @computed_field  # type: ignore[prop-decorator]
     @property