domain repos for PE numbers and task orders

atst/domain/pe_numbers.py

@@ -0,0 +1,15 @@
+from atst.models.pe_number import PENumber
+from .exceptions import NotFoundError
+
+
+class PENumbers(object):
+
+    def __init__(self, db_session):
+        self.db_session = db_session
+
+    def get(self, number):
+        pe_number = self.db_session.query(PENumber).get(number)
+        if not pe_number:
+            raise NotFoundError("pe_number")
+
+        return pe_number