Added get_single_monkey_by_id API to the monkey model

Useful in many cases in the code.
Also added unittest for this method which passed.

monkey/monkey_island/cc/models/errors.py

@@ -0,0 +1,2 @@
+class MonkeyNotFoundError(Exception):
+    pass

monkey/monkey_island/cc/models/monkey.py

@@ -5,6 +5,7 @@ import mongoengine
 from mongoengine import Document, StringField, ListField, BooleanField, EmbeddedDocumentField, DateField, \
     ReferenceField
 
+from monkey_island.cc.models.errors import MonkeyNotFoundError
 from monkey_island.cc.models.monkey_ttl import MonkeyTtl
 
 
@@ -32,6 +33,13 @@ class Monkey(Document):
     pba_results = ListField()
     ttl_ref = ReferenceField(MonkeyTtl)
 
+    @staticmethod
+    def get_single_monkey_by_id(db_id):
+        try:
+            return Monkey.objects(id=db_id)[0]
+        except IndexError:
+            raise MonkeyNotFoundError("id: {0}".format(str(db_id)))
+
     def is_dead(self):
         monkey_is_dead = False
         if self.dead:
@@ -41,7 +49,7 @@ class Monkey(Document):
                 if MonkeyTtl.objects(id=self.ttl_ref.id).count() == 0:
                     # No TTLs - monkey has timed out. The monkey is MIA.
                     monkey_is_dead = True
-            except mongoengine.DoesNotExist:
+            except (mongoengine.DoesNotExist, AttributeError):
                 # Trying to dereference unknown document - the monkey is MIA.
                 monkey_is_dead = True
         return monkey_is_dead

monkey/monkey_island/cc/models/test_monkey.py

@@ -7,6 +7,7 @@ from unittest import TestCase
 import mongomock
 
 from monkey import Monkey
+from monkey_island.cc.models.errors import MonkeyNotFoundError
 from monkey_ttl import MonkeyTtl
 
 
@@ -35,3 +36,9 @@ class TestMonkey(TestCase):
         self.assertTrue(mia_monkey.is_dead())
         self.assertFalse(alive_monkey.is_dead())
 
+    def test_get_single_monkey_by_id(self):
+        a_monkey = Monkey(guid=str(uuid.uuid4()))
+        a_monkey.save()
+
+        self.assertIsNotNone(Monkey.get_single_monkey_by_id(a_monkey.id))
+        self.assertRaises(MonkeyNotFoundError, Monkey.get_single_monkey_by_id, "abcdefabcdefabcdefabcdef")