Significant refactorings

src/alpine_bits_python/db.py

@@ -22,7 +22,7 @@ from sqlalchemy.ext.asyncio import (
     async_sessionmaker,
     create_async_engine,
 )
-from sqlalchemy.orm import declarative_base, relationship
+from sqlalchemy.orm import backref, declarative_base, relationship
 
 from .logging_config import get_logger
 
@@ -347,7 +347,7 @@ class HashedCustomer(Base):
     __tablename__ = "hashed_customers"
     id = Column(Integer, primary_key=True)
     customer_id = Column(
-        Integer, ForeignKey("customers.id"), unique=True, nullable=False
+        Integer, ForeignKey("customers.id", ondelete="SET NULL"), unique=True, nullable=True
     )
     contact_id = Column(String, unique=True)  # Keep unhashed for reference
     hashed_email = Column(String(64))  # SHA256 produces 64 hex chars
@@ -361,7 +361,7 @@ class HashedCustomer(Base):
     hashed_birth_date = Column(String(64))
     created_at = Column(DateTime(timezone=True))
 
-    customer = relationship("Customer", backref="hashed_version")
+    customer = relationship("Customer", backref=backref("hashed_version", uselist=False, lazy="joined"))
 
 
 class ConversionGuest(Base):
@@ -477,7 +477,7 @@ class ConversionGuest(Base):
 class Reservation(Base):
     __tablename__ = "reservations"
     id = Column(Integer, primary_key=True)
-    customer_id = Column(Integer, ForeignKey("customers.id"))
+    customer_id = Column(Integer, ForeignKey("customers.id", ondelete="SET NULL"))
     unique_id = Column(String, unique=True)
     md5_unique_id = Column(String(32), unique=True)  # max length 32 guaranteed
     start_date = Column(Date)