[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_packages_util.py

@@ -26,17 +26,21 @@ def setup():
 @pytest.fixture
 def maintainer() -> User:
     account_type = db.query(AccountType, AccountType.ID == USER_ID).first()
-    yield db.create(User, Username="test_maintainer",
-                    Email="test_maintainer@examepl.org",
-                    Passwd="testPassword",
-                    AccountType=account_type)
+    with db.begin():
+        maintainer = db.create(User, Username="test_maintainer",
+                               Email="test_maintainer@examepl.org",
+                               Passwd="testPassword",
+                               AccountType=account_type)
+    yield maintainer
 
 
 @pytest.fixture
 def package(maintainer: User) -> Package:
-    pkgbase = db.create(PackageBase, Name="test-pkg",
-                        Packager=maintainer, Maintainer=maintainer)
-    yield db.create(Package, Name=pkgbase.Name, PackageBase=pkgbase)
+    with db.begin():
+        pkgbase = db.create(PackageBase, Name="test-pkg",
+                            Packager=maintainer, Maintainer=maintainer)
+        package = db.create(Package, Name=pkgbase.Name, PackageBase=pkgbase)
+    yield package
 
 
 @pytest.fixture
@@ -45,10 +49,11 @@ def client() -> TestClient:
 
 
 def test_package_link(client: TestClient, maintainer: User, package: Package):
-    db.create(OfficialProvider,
-              Name=package.Name,
-              Repo="core",
-              Provides=package.Name)
+    with db.begin():
+        db.create(OfficialProvider,
+                  Name=package.Name,
+                  Repo="core",
+                  Provides=package.Name)
     expected = f"{OFFICIAL_BASE}/packages/?q={package.Name}"
     assert util.package_link(package) == expected