domain repos for PE numbers and task orders

atst/domain/task_orders.py

@@ -0,0 +1,18 @@
+from sqlalchemy.orm.exc import NoResultFound
+
+from atst.models.task_order import TaskOrder
+from .exceptions import NotFoundError
+
+
+class TaskOrders(object):
+
+    def __init__(self, db_session):
+        self.db_session = db_session
+
+    def get(self, order_number):
+        try:
+            task_order = self.db_session.query(TaskOrder).filter_by(number=order_number).one()
+        except NoResultFound:
+            raise NotFoundError("task_order")
+
+        return task_order