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app/db/session.py

@@ -1,9 +1,21 @@
-from sqlalchemy import create_engine
+from sqlalchemy import create_engine, inspect, text
 from sqlalchemy.engine import Engine
 from sqlalchemy.orm import Session, sessionmaker
 
 from app.db.models import Base
 
+# Columns added to existing tables after their initial release. create_all()
+# only creates missing tables, never adds columns to tables that already
+# exist, so a column added to a model here must also be listed below or an
+# already-deployed database will never receive it and the app will crash
+# reading/writing that column.
+_ADDITIVE_COLUMNS: dict[str, list[tuple[str, str]]] = {
+    "sync_users": [
+        ("notify_email_enabled", "BOOLEAN NOT NULL DEFAULT 0"),
+        ("notification_email", "VARCHAR(255)"),
+    ],
+}
+
 
 def create_db_engine(database_url: str) -> Engine:
     connect_args = {"check_same_thread": False} if database_url.startswith("sqlite") else {}
@@ -16,3 +28,24 @@ def create_session_factory(engine: Engine) -> sessionmaker[Session]:
 
 def initialize_schema(engine: Engine) -> None:
     Base.metadata.create_all(engine)
+    _apply_additive_migrations(engine)
+
+
+def _apply_additive_migrations(engine: Engine) -> None:
+    if engine.dialect.name != "sqlite":
+        # ALTER TABLE ... ADD COLUMN syntax/type names below are only
+        # verified against sqlite, the only backend this app is deployed
+        # against; a fresh create_all() on another backend already has every
+        # current column, so skipping here only matters for a pre-existing
+        # non-sqlite database, which does not exist in practice.
+        return
+    inspector = inspect(engine)
+    existing_tables = set(inspector.get_table_names())
+    with engine.begin() as conn:
+        for table, columns in _ADDITIVE_COLUMNS.items():
+            if table not in existing_tables:
+                continue
+            existing_columns = {col["name"] for col in inspector.get_columns(table)}
+            for name, ddl_type in columns:
+                if name not in existing_columns:
+                    conn.execute(text(f"ALTER TABLE {table} ADD COLUMN {name} {ddl_type}"))