Multi Dependency Support [Internal API Changes] (#1147)

* Convert `_dependency_id` to `_dependency_ids`

Change `Job`s tracking from a single id of it's dependencies from a single _id_ to a list of _id_s. This change should be private to `Job` - especially leaving `Job#to_dict` and `Job#restore`s treatment of a single 'dependency_id' intact.

This change modifies existing tests.

* Remove reliance upon dependency property in tests

... use dependency.id not  `_dependency_id`

* Re-add assertions for Falsey Values

* Add _dependency_id property

For backwards compatibility with other libs such as django-rq and rq-scheduler

rq/job.py

@@ -137,7 +137,7 @@ class Job(object):
 
         # dependency could be job instance or id
         if depends_on is not None:
-            job._dependency_id = depends_on.id if isinstance(depends_on, Job) else depends_on
+            job._dependency_ids = [depends_on.id if isinstance(depends_on, Job) else depends_on]
         return job
 
     def get_status(self):
@@ -169,16 +169,24 @@ class Job(object):
     def is_deferred(self):
         return self.get_status() == JobStatus.DEFERRED
 
+    @property
+    def _dependency_id(self):
+        """Returns the first item in self._dependency_ids. Present
+        preserve compatibility with third party packages..
+        """
+        if self._dependency_ids:
+            return self._dependency_ids[0]
+
     @property
     def dependency(self):
         """Returns a job's dependency. To avoid repeated Redis fetches, we cache
         job.dependency as job._dependency.
         """
-        if self._dependency_id is None:
+        if not self._dependency_ids:
             return None
         if hasattr(self, '_dependency'):
             return self._dependency
-        job = self.fetch(self._dependency_id, connection=self.connection)
+        job = self.fetch(self._dependency_ids[0], connection=self.connection)
         self._dependency = job
         return job
 
@@ -328,7 +336,7 @@ class Job(object):
         self.failure_ttl = None
         self.ttl = None
         self._status = None
-        self._dependency_id = None
+        self._dependency_ids = []
         self.meta = {}
 
     def __repr__(self):  # noqa  # pragma: no cover
@@ -437,7 +445,10 @@ class Job(object):
         self.result_ttl = int(obj.get('result_ttl')) if obj.get('result_ttl') else None  # noqa
         self.failure_ttl = int(obj.get('failure_ttl')) if obj.get('failure_ttl') else None  # noqa
         self._status = obj.get('status') if obj.get('status') else None
-        self._dependency_id = as_text(obj.get('dependency_id', None))
+
+        dependency_id = obj.get('dependency_id', None)
+        self._dependency_ids = [as_text(dependency_id)] if dependency_id else []
+
         self.ttl = int(obj.get('ttl')) if obj.get('ttl') else None
         self.meta = unpickle(obj.get('meta')) if obj.get('meta') else {}
 
@@ -497,8 +508,8 @@ class Job(object):
             obj['failure_ttl'] = self.failure_ttl
         if self._status is not None:
             obj['status'] = self._status
-        if self._dependency_id is not None:
-            obj['dependency_id'] = self._dependency_id
+        if self._dependency_ids:
+            obj['dependency_id'] = self._dependency_ids[0]
         if self.meta and include_meta:
             obj['meta'] = dumps(self.meta)
         if self.ttl:
@@ -683,7 +694,9 @@ class Job(object):
         registry.add(self, pipeline=pipeline)
 
         connection = pipeline if pipeline is not None else self.connection
-        connection.sadd(self.dependents_key_for(self._dependency_id), self.id)
 
+        for dependency_id in self._dependency_ids:
+            dependents_key = self.dependents_key_for(dependency_id)
+            connection.sadd(dependents_key, self.id)
 
 _job_stack = LocalStack()

tests/test_decorator.py

@@ -4,11 +4,11 @@ from __future__ import (absolute_import, division, print_function,
 
 import mock
 from redis import Redis
+
 from rq.decorators import job
 from rq.job import Job
-from rq.worker import DEFAULT_RESULT_TTL
 from rq.queue import Queue
-
+from rq.worker import DEFAULT_RESULT_TTL
 from tests import RQTestCase
 from tests.fixtures import decorated_job
 
@@ -109,11 +109,12 @@ class TestDecorator(RQTestCase):
 
         bar_job = bar.delay()
 
+        self.assertEqual(foo_job._dependency_ids,[])
         self.assertIsNone(foo_job._dependency_id)
 
+        self.assertEqual(foo_job.dependency, None)
         self.assertEqual(bar_job.dependency, foo_job)
-
-        self.assertEqual(bar_job._dependency_id, foo_job.id)
+        self.assertEqual(bar_job.dependency.id, foo_job.id)
 
     def test_decorator_delay_accepts_depends_on_as_argument(self):
         """Ensure that passing in depends_on to the delay method of
@@ -145,8 +146,11 @@ class TestDecorator(RQTestCase):
         self.assertIsNone(foo_job._dependency_id)
         self.assertIsNone(bar_job._dependency_id)
 
-        self.assertEqual(baz_job.dependency, bar_job)
+        self.assertEqual(foo_job._dependency_ids,[])
+        self.assertEqual(bar_job._dependency_ids,[])
         self.assertEqual(baz_job._dependency_id, bar_job.id)
+        self.assertEqual(baz_job.dependency, bar_job)
+        self.assertEqual(baz_job.dependency.id, bar_job.id)
 
     @mock.patch('rq.queue.resolve_connection')
     def test_decorator_connection_laziness(self, resolve_connection):

tests/test_job.py

@@ -2,28 +2,28 @@
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 
-from datetime import datetime
-
-import time
 import sys
+import time
 import zlib
-
-is_py2 = sys.version[0] == '2'
-if is_py2:
-    import Queue as queue
-else:
-    import queue as queue
-
-from tests import fixtures, RQTestCase
+from datetime import datetime
 
 from rq.compat import PY2, as_text
 from rq.exceptions import NoSuchJobError, UnpickleError
-from rq.job import Job, get_current_job, JobStatus, cancel_job
+from rq.job import Job, JobStatus, cancel_job, get_current_job
 from rq.queue import Queue
 from rq.registry import (DeferredJobRegistry, FailedJobRegistry,
                          FinishedJobRegistry, StartedJobRegistry)
 from rq.utils import utcformat
 from rq.worker import Worker
+from tests import RQTestCase, fixtures
+
+is_py2 = sys.version[0] == '2'
+if is_py2:
+    import Queue as queue
+else:
+    import queue as queue
+
+
 
 try:
     from cPickle import loads, dumps
@@ -227,12 +227,16 @@ class TestJob(RQTestCase):
         job.save()
         stored_job = Job.fetch(job.id)
         self.assertEqual(stored_job._dependency_id, parent_job.id)
+        self.assertEqual(stored_job._dependency_ids, [parent_job.id])
+        self.assertEqual(stored_job.dependency.id, parent_job.id)
         self.assertEqual(stored_job.dependency, parent_job)
 
         job = Job.create(func=fixtures.some_calculation, depends_on=parent_job.id)
         job.save()
         stored_job = Job.fetch(job.id)
         self.assertEqual(stored_job._dependency_id, parent_job.id)
+        self.assertEqual(stored_job._dependency_ids, [parent_job.id])
+        self.assertEqual(stored_job.dependency.id, parent_job.id)
         self.assertEqual(stored_job.dependency, parent_job)
 
     def test_store_then_fetch(self):