Subclass the Transaction with multiple children

Each children is essentually a type of transaction. We currently have:
- bank transactions
- money transactions
- split transactions

The table inheritance is implemented as a single table, with a
polymorphic type and Null columns.

Adds a IsSplit interface, which will later be used for the category
views, so as to not repeat transactions.

alembic/versions/37d80de801a7_inheritance.py

@@ -0,0 +1,74 @@
+"""Inheritance
+
+Revision ID: 37d80de801a7
+Revises: 8cc9870b0d74
+Create Date: 2023-01-10 22:41:03.540108+00:00
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "37d80de801a7"
+down_revision = "8cc9870b0d74"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column(
+        "originals",
+        sa.Column("type", sa.String(), nullable=False),
+        schema="transactions",
+    )
+    op.add_column(
+        "originals",
+        sa.Column("split", sa.Boolean(), nullable=True),
+        schema="transactions",
+    )
+    op.add_column(
+        "originals",
+        sa.Column("original", sa.BigInteger(), nullable=True),
+        schema="transactions",
+    )
+    op.alter_column(
+        "originals",
+        "bank",
+        existing_type=sa.TEXT(),
+        nullable=True,
+        schema="transactions",
+    )
+    op.create_foreign_key(
+        op.f("fk_originals_original_originals"),
+        "originals",
+        "originals",
+        ["original"],
+        ["id"],
+        source_schema="transactions",
+        referent_schema="transactions",
+        ondelete="CASCADE",
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_constraint(
+        op.f("fk_originals_original_originals"),
+        "originals",
+        schema="transactions",
+        type_="foreignkey",
+    )
+    op.alter_column(
+        "originals",
+        "bank",
+        existing_type=sa.TEXT(),
+        nullable=False,
+        schema="transactions",
+    )
+    op.drop_column("originals", "original", schema="transactions")
+    op.drop_column("originals", "split", schema="transactions")
+    op.drop_column("originals", "type", schema="transactions")
+    # ### end Alembic commands ###

pfbudget/db/model.py

@@ -74,14 +74,17 @@ class Transaction(Base):
     id: Mapped[idpk] = mapped_column(init=False)
     date: Mapped[dt.date]
     description: Mapped[Optional[str]]
-    bank: Mapped[bankfk]
     amount: Mapped[money]
 
+    type: Mapped[str] = mapped_column(init=False)
+
     category: Mapped[Optional[TransactionCategory]] = relationship(init=False)
     note: Mapped[Optional[Note]] = relationship(init=False)
     tags: Mapped[Optional[set[TransactionTag]]] = relationship(init=False)
 
-    def __lt__(self, other):
+    __mapper_args__ = {"polymorphic_on": "type", "polymorphic_identity": "transaction"}
+
+    def __lt__(self, other: Transaction):
         return self.date < other.date
 
 
@@ -90,6 +93,26 @@ idfk = Annotated[
 ]
 
 
+class IsSplit:
+    split: Mapped[bool] = mapped_column(use_existing_column=True, nullable=True)
+
+
+class BankTransaction(IsSplit, Transaction):
+    bank: Mapped[bankfk] = mapped_column(nullable=True)
+
+    __mapper_args__ = {"polymorphic_identity": "bank", "polymorphic_load": "inline"}
+
+
+class MoneyTransaction(IsSplit, Transaction):
+    __mapper_args__ = {"polymorphic_identity": "money"}
+
+
+class SplitTransaction(Transaction):
+    original: Mapped[idfk] = mapped_column(nullable=True)
+
+    __mapper_args__ = {"polymorphic_identity": "split", "polymorphic_load": "inline"}
+
+
 class CategoryGroup(Base):
     __tablename__ = "categories_groups"
 

pfbudget/input/nordigen.py

@@ -7,7 +7,7 @@ from uuid import uuid4
 import json
 import os
 
-from pfbudget.db.model import Transaction
+from pfbudget.db.model import BankTransaction
 from pfbudget.utils import convert
 
 from .input import Input
@@ -29,7 +29,7 @@ class NordigenInput(Input):
         self._start = date.min
         self._end = date.max
 
-    def parse(self) -> list[Transaction]:
+    def parse(self) -> list[BankTransaction]:
         transactions = []
         assert len(self._banks) > 0
 

pfbudget/utils/converters.py

@@ -1,8 +1,8 @@
-from datetime import date, timedelta
+from datetime import date
 from functools import singledispatch
 
 from pfbudget.common.types import TransactionError
-from pfbudget.db.model import Bank, Transaction
+from pfbudget.db.model import Bank, BankTransaction
 from .utils import parse_decimal
 
 
@@ -13,10 +13,10 @@ def convert(t):
 
 
 @convert.register
-def _(json: dict, bank: Bank) -> Transaction:
+def _(json: dict, bank: Bank) -> BankTransaction:
     i = -1 if bank.nordigen.invert else 1
     try:
-        transaction = Transaction(
+        transaction = BankTransaction(
             date=date.fromisoformat(json["bookingDate"]),
             description=json["remittanceInformationUnstructured"],
             bank=bank.name,