fix: add explicit ondelete behavior to alert FK references

fablednetmon/models/alerts.py

@@ -36,7 +36,7 @@ class AlertRule(Base):
     threshold: Mapped[float] = mapped_column(Float, nullable=False)
     consecutive_failures_required: Mapped[int] = mapped_column(Integer, nullable=False, default=1)
     enabled: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
-    created_by: Mapped[str] = mapped_column(String(36), ForeignKey("users.id"), nullable=False)
+    created_by: Mapped[str] = mapped_column(String(36), ForeignKey("users.id", ondelete="RESTRICT"), nullable=False)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, default=lambda: datetime.now(timezone.utc)
     )
@@ -57,7 +57,7 @@ class AlertState(Base):
         DateTime(timezone=True), nullable=False, default=lambda: datetime.now(timezone.utc)
     )
     acknowledged_by: Mapped[str | None] = mapped_column(
-        String(36), ForeignKey("users.id"), nullable=True
+        String(36), ForeignKey("users.id", ondelete="SET NULL"), nullable=True
     )
     acknowledged_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)