some refactoring

src/models/category.py

@@ -1,8 +1,8 @@
 from pydantic import Field, computed_field
 from sqlalchemy import ForeignKey, String, UniqueConstraint
-from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.orm import Mapped, Session, mapped_column, relationship
 
-from src.models._common import BaseModelDb, ExportBaseModel, _hash
+from src.models.common import BaseModelDb, ExportBaseModel, hashify
 
 
 class Category(ExportBaseModel):
@@ -12,7 +12,7 @@ class Category(ExportBaseModel):
     @computed_field  # type: ignore[prop-decorator]
     @property
     def hash_id(self) -> str:
-        return _hash(self.name, self.parent)
+        return hashify(self.name, self.parent)
 
     @classmethod
     def from_str(cls, s: str) -> Category | None:
@@ -54,3 +54,8 @@ class CategoryDb(BaseModelDb):
     )
     children = relationship("CategoryDb", back_populates="parent")
     budgets = relationship("CategoryBudgetDb", back_populates="category")
+
+
+def add_category(session: Session, category_name: str):
+    category = Category.from_str(category_name)
+    session.add(category)