Fix data race when creating sessions

Fixes the following exception:

    Traceback (most recent call last):
    File "/venv/lib64/python3.12/site-packages/sqlalchemy/engine/base.py", line 1967, in _exec_single_context
        self.dialect.do_execute(
    File "/venv/lib64/python3.12/site-packages/sqlalchemy/engine/default.py", line 941, in do_execute
        cursor.execute(statement, parameters)
    psycopg2.errors.UniqueViolation: duplicate key value violates unique constraint "pg_class_relname_nsp_index"
    DETAIL:  Key (relname, relnamespace)=(sessions_id_seq, 2200) already exists.

docs/api.rst

@@ -10,6 +10,6 @@ WavierDB offers a HTTP REST API.
 REST API
 ========
 
-.. autoflask:: waiverdb.app:create_app(config_obj='waiverdb.config.DevelopmentConfig',create_session=False)
+.. autoflask:: waiverdb.app:create_app(config_obj='waiverdb.config.DevelopmentConfig')
     :undoc-static:
     :order: path

tests/test_app.py

@@ -24,7 +24,7 @@ class EnabledMessagedConfig(config.Config):
 
 @patch("waiverdb.app.event.listen")
 def test_disabled_messaging_should_not_register_events(mock_listen):
-    app.create_app(DisabledMessagingConfig, create_session=False)
+    app.create_app(DisabledMessagingConfig)
     calls = [
         c for c in mock_listen.mock_calls if c == call(ANY, ANY, app.publish_new_waiver)
     ]
@@ -33,7 +33,7 @@ def test_disabled_messaging_should_not_register_events(mock_listen):
 
 @patch("waiverdb.app.event.listen")
 def test_enabled_messaging_should_register_events(mock_listen):
-    app.create_app(EnabledMessagedConfig, create_session=False)
+    app.create_app(EnabledMessagedConfig)
     calls = [
         c for c in mock_listen.mock_calls if c == call(ANY, ANY, app.publish_new_waiver)
     ]

waiverdb/app.py

@@ -8,13 +8,13 @@
 except ImportError:
     from urlparse import urlparse, urlunsplit
 
+import sqlalchemy
 from flask import Flask, current_app, send_from_directory
 from flask_cors import CORS
 from flask_migrate import Migrate
 from flask_pydantic.exceptions import ValidationError
 from flask_session import Session
 from flask_wtf.csrf import CSRFProtect
-from sqlalchemy import event, text
 from sqlalchemy.exc import ProgrammingError
 import requests
 
@@ -90,7 +90,7 @@ def populate_db_config(app):
 
 
 # applicaiton factory http://flask.pocoo.org/docs/0.12/patterns/appfactories/
-def create_app(config_obj=None, create_session=True):
+def create_app(config_obj=None):
     app = Flask(__name__)
     csrf.init_app(app)
 
@@ -120,9 +120,7 @@ def create_app(config_obj=None, create_session=True):
     # initialize db
     db.init_app(app)
     # initialize session
-    app.config["SESSION_SQLALCHEMY"] = db
-    if create_session:
-        Session(app)
+    init_session(app)
     # initialize tracing
     with app.app_context():
         init_tracing(app, db.engine)
@@ -146,6 +144,17 @@ def create_app(config_obj=None, create_session=True):
     return app
 
 
+def init_session(app):
+    app.config["SESSION_SQLALCHEMY"] = db
+    app.server_session = Session(app)
+    if app.config["SESSION_TYPE"] == "sqlalchemy":
+        with app.app_context():
+            inspect = sqlalchemy.inspect(db.engine)
+            table = app.config["SESSION_SQLALCHEMY_TABLE"]
+            if not inspect.has_table(table):
+                db.create_all()
+
+
 def healthcheck():
     """
     Request handler for performing an application-level health check. This is
@@ -155,7 +164,7 @@ def healthcheck():
     Returns a 200 response if the application is alive and able to serve requests.
     """
     try:
-        db.session.execute(text("SELECT 1 FROM waiver LIMIT 0")).fetchall()
+        db.session.execute(sqlalchemy.text("SELECT 1 FROM waiver LIMIT 0")).fetchall()
     except ProgrammingError:
         current_app.logger.exception('Healthcheck failed on DB query.')
         raise RuntimeError('Unable to communicate with database.')
@@ -180,7 +189,7 @@ def register_event_handlers(app):
             attached as the ``session`` attribute.
     """
     if app.config['MESSAGE_BUS_PUBLISH']:
-        event.listen(db.session, 'after_commit', publish_new_waiver)
+        sqlalchemy.event.listen(db.session, 'after_commit', publish_new_waiver)
 
 
 def favicon():

waiverdb/manage.py

@@ -4,15 +4,11 @@
 import click
 from flask.cli import FlaskGroup
 from sqlalchemy.exc import OperationalError
+from waiverdb.app import create_app
 from waiverdb.models import db
 
 
-def create_waiver_app():
-    from waiverdb.app import create_app  # noqa: F401
-    return create_app(create_session=False)
-
-
-@click.group(cls=FlaskGroup, create_app=create_waiver_app)
+@click.group(cls=FlaskGroup, create_app=create_app)
 def cli():
     pass