add PackageGroup SQLAlchemy ORM model

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

aurweb/models/package_group.py

+from sqlalchemy.orm import mapper
+
+from aurweb.db import make_relationship
+from aurweb.models.group import Group
+from aurweb.models.package import Package
+from aurweb.schema import PackageGroups
+
+
+class PackageGroup:
+    def __init__(self, Package: Package = None, Group: Group = None):
+        self.Package = Package
+        self.Group = Group
+
+
+properties = {
+    "Package": make_relationship(Package,
+                                 PackageGroups.c.PackageID,
+                                 "package_group",
+                                 uselist=False),
+    "Group": make_relationship(Group,
+                               PackageGroups.c.GroupID,
+                               "package_group",
+                               uselist=False)
+}
+
+mapper(PackageGroup, PackageGroups, properties=properties,
+       primary_key=[PackageGroups.c.PackageID, PackageGroups.c.GroupID])

test/test_package_group.py

+import pytest
+
+from sqlalchemy.exc import IntegrityError
+
+from aurweb.db import create, query
+from aurweb.models.account_type import AccountType
+from aurweb.models.group import Group
+from aurweb.models.package import Package
+from aurweb.models.package_base import PackageBase
+from aurweb.models.package_group import PackageGroup
+from aurweb.models.user import User
+from aurweb.testing import setup_test_db
+
+user = group = pkgbase = package = None
+
+
+@pytest.fixture(autouse=True)
+def setup():
+    global user, group, pkgbase, package
+
+    setup_test_db("Users", "PackageBases", "Packages",
+                  "Groups", "PackageGroups")
+
+    account_type = query(AccountType,
+                         AccountType.AccountType == "User").first()
+    user = create(User, Username="test", Email="test@example.org",
+                  RealName="Test User", Passwd="testPassword",
+                  account_type=account_type)
+
+    group = create(Group, Name="Test Group")
+    pkgbase = create(PackageBase, Name="test-package", Maintainer=user)
+    package = create(Package, PackageBase=pkgbase, Name=pkgbase.Name)
+
+
+def test_package_group():
+    package_group = create(PackageGroup, Package=package, Group=group)
+    assert package_group.Group == group
+    assert package_group.Package == package
+
+
+def test_package_group_null_package_raises_exception():
+    from aurweb.db import session
+    with pytest.raises(IntegrityError):
+        create(PackageGroup, Group=group)
+    session.rollback()
+
+
+def test_package_group_null_group_raises_exception():
+    from aurweb.db import session
+    with pytest.raises(IntegrityError):
+        create(PackageGroup, Package=package)
+    session.rollback()