add PackageSource SQLAlchemy ORM model

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

aurweb/models/package_source.py

@@ -0,0 +1,31 @@
+from sqlalchemy import Column, ForeignKey, Integer
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.orm import backref, relationship
+
+import aurweb.models.package
+
+from aurweb.models.declarative import Base
+
+
+class PackageSource(Base):
+    __tablename__ = "PackageSources"
+
+    PackageID = Column(Integer, ForeignKey("Packages.ID", ondelete="CASCADE"),
+                       nullable=False)
+    Package = relationship(
+        "Package", backref=backref("package_sources", lazy="dynamic"),
+        foreign_keys=[PackageID])
+
+    __mapper_args__ = {"primary_key": [PackageID]}
+
+    def __init__(self,
+                 Package: aurweb.models.package.Package = None,
+                 **kwargs):
+        super().__init__(**kwargs)
+
+        self.Package = Package
+        if not self.Package:
+            raise IntegrityError(
+                statement="Foreign key PackageID cannot be null.",
+                orig="PackageSources.PackageID",
+                params=("NULL"))