[FastAPI] Refactor db modifications

For SQLAlchemy to automatically understand updates from the
external world, it must use an `autocommit=True` in its session.

This change breaks how we were using commit previously, as
`autocommit=True` causes SQLAlchemy to commit when a
SessionTransaction context hits __exit__.

So, a refactoring was required of our tests: All usage of
any `db.{create,delete}` must be called **within** a
SessionTransaction context, created via new `db.begin()`.

From this point forward, we're going to require:

```
with db.begin():
    db.create(...)
    db.delete(...)
    db.session.delete(object)
```

With this, we now get external DB modifications automatically
without reloading or restarting the FastAPI server, which we
absolutely need for production.

Signed-off-by: Kevin Morris <kevr@0cost.org>

test/test_db.py

@@ -278,18 +278,15 @@ def test_connection_execute_paramstyle_unsupported():
 
 
 def test_create_delete():
-    db.create(AccountType, AccountType="test")
+    with db.begin():
+        db.create(AccountType, AccountType="test")
+
     record = db.query(AccountType, AccountType.AccountType == "test").first()
     assert record is not None
-    db.delete(AccountType, AccountType.AccountType == "test")
-    record = db.query(AccountType, AccountType.AccountType == "test").first()
-    assert record is None
 
-    # Create and delete a record with autocommit=False.
-    db.create(AccountType, AccountType="test", autocommit=False)
-    db.commit()
-    db.delete(AccountType, AccountType.AccountType == "test", autocommit=False)
-    db.commit()
+    with db.begin():
+        db.delete(AccountType, AccountType.AccountType == "test")
+
     record = db.query(AccountType, AccountType.AccountType == "test").first()
     assert record is None
 
@@ -297,8 +294,8 @@ def test_create_delete():
 def test_add_commit():
     # Use db.add and db.commit to add a temporary record.
     account_type = AccountType(AccountType="test")
-    db.add(account_type)
-    db.commit()
+    with db.begin():
+        db.add(account_type)
 
     # Assert it got created in the DB.
     assert bool(account_type.ID)
@@ -308,7 +305,8 @@ def test_add_commit():
     assert record == account_type
 
     # Remove the record.
-    db.delete(AccountType, AccountType.ID == account_type.ID)
+    with db.begin():
+        db.delete(AccountType, AccountType.ID == account_type.ID)
 
 
 def test_connection_executor_mysql_paramstyle():