Add System<->Manager linkage

Redfish data model rests on three interlinked
entities - ComputerSystem(s), Manager(s) and Chassis. As of this
moment, sushy does not support traversing between these entities
at the Sushy abstraction level, despite the availability of such
linkage in the JSON documents sushy feeds on.

This change establishes System->Managers and Managers->System
links.

Change-Id: I54b0fdeebdea1e13c2b6912ee4c97776ebccaf03
Story: 2004512
Task: 28240

releasenotes/notes/add-system-manager-linkage-86be69c9df4cb359.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Establishes ComputerSystem->Managers and Manager->ComputerSystems
+    references at sushy data abstraction level what make it possible to
+    look up Manager(s) responsible for a ComputerSystem and vice versa.

sushy/resources/manager/manager.py

@@ -188,6 +188,25 @@ class Manager(base.ResourceBase):
             self._conn, utils.get_sub_resource_path_by(self, 'VirtualMedia'),
             redfish_version=self.redfish_version)
 
+    @property
+    @utils.cache_it
+    def systems(self):
+        """A list of systems managed by this manager.
+
+        Returns a list of `System` objects representing systems being
+        managed by this manager.
+
+        :raises: MissingAttributeError if '@odata.id' field is missing.
+        :returns: A list of `System` instances
+        """
+        paths = utils.get_sub_resource_path_by(
+            self, ["Links", "ManagerForServers"], is_collection=True)
+
+        from sushy.resources.system import system
+        return [system.System(self._conn, path,
+                              redfish_version=self.redfish_version)
+                for path in paths]
+
 
 class ManagerCollection(base.ResourceCollectionBase):
 

sushy/resources/system/system.py

@@ -18,6 +18,7 @@ import logging
 from sushy import exceptions
 from sushy.resources import base
 from sushy.resources import common
+from sushy.resources.manager import manager
 from sushy.resources import mappings as res_maps
 from sushy.resources.system import bios
 from sushy.resources.system import constants as sys_cons
@@ -333,6 +334,24 @@ class System(base.ResourceBase):
             self._conn, utils.get_sub_resource_path_by(self, "Storage"),
             redfish_version=self.redfish_version)
 
+    @property
+    @utils.cache_it
+    def managers(self):
+        """A list of managers for this system.
+
+        Returns a list of `Manager` objects representing the managers
+        that manage this system.
+
+        :raises: MissingAttributeError if '@odata.id' field is missing.
+        :returns: A list of `Manager` instances
+        """
+        paths = utils.get_sub_resource_path_by(
+            self, ["Links", "ManagedBy"], is_collection=True)
+
+        return [manager.Manager(self._conn, path,
+                                redfish_version=self.redfish_version)
+                for path in paths]
+
 
 class SystemCollection(base.ResourceCollectionBase):
 

sushy/tests/unit/resources/manager/test_manager.py

@@ -18,6 +18,7 @@ import sushy
 from sushy import exceptions
 from sushy.resources.manager import manager
 from sushy.resources.manager import virtual_media
+from sushy.resources.system import system
 from sushy.tests.unit import base
 
 
@@ -265,6 +266,18 @@ class ManagerTestCase(base.TestCase):
                               virtual_media.VirtualMediaCollection)
         self.assertFalse(vrt_media._is_stale)
 
+    def test_systems(self):
+        # | GIVEN |
+        with open('sushy/tests/unit/json_samples/'
+                  'system.json') as f:
+            self.conn.get.return_value.json.return_value = json.load(f)
+
+        # | WHEN & THEN |
+        actual_systems = self.manager.systems
+        self.assertIsInstance(actual_systems[0], system.System)
+        self.assertEqual(
+            '/redfish/v1/Systems/437XR1138R2', actual_systems[0].path)
+
 
 class ManagerCollectionTestCase(base.TestCase):
 

sushy/tests/unit/resources/system/test_system.py

@@ -20,6 +20,7 @@ import mock
 import sushy
 from sushy import exceptions
 from sushy.resources import constants as res_cons
+from sushy.resources.manager import manager
 from sushy.resources.system import bios
 from sushy.resources.system import mappings as sys_map
 from sushy.resources.system import processor
@@ -478,6 +479,18 @@ class SystemTestCase(base.TestCase):
         # | WHEN & THEN |
         self.assertIsInstance(self.sys_inst.storage, storage.StorageCollection)
 
+    def test_managers(self):
+        # | GIVEN |
+        with open('sushy/tests/unit/json_samples/'
+                  'manager.json') as f:
+            self.conn.get.return_value.json.return_value = json.load(f)
+
+        # | WHEN & THEN |
+        actual_managers = self.sys_inst.managers
+        self.assertIsInstance(actual_managers[0], manager.Manager)
+        self.assertEqual(
+            '/redfish/v1/Managers/BMC', actual_managers[0].path)
+
 
 class SystemCollectionTestCase(base.TestCase):
 

sushy/tests/unit/test_utils.py

@@ -69,6 +69,14 @@ class UtilsTestCase(base.TestCase):
                                                subresource_path)
         self.assertEqual(expected_result, value)
 
+    def test_get_sub_resource_path_by_collection(self):
+        subresource_path = ["Links", "ManagedBy"]
+        expected_result = ['/redfish/v1/Managers/BMC']
+        value = utils.get_sub_resource_path_by(self.sys_inst,
+                                               subresource_path,
+                                               is_collection=True)
+        self.assertEqual(expected_result, value)
+
     def test_get_sub_resource_path_by_fails(self):
         subresource_path = ['Links', 'Chassis']
         expected_result = 'attribute Links/Chassis/@odata.id is missing'

sushy/utils.py

@@ -66,13 +66,17 @@ def int_or_none(x):
     return int(x)
 
 
-def get_sub_resource_path_by(resource, subresource_name):
+def get_sub_resource_path_by(resource, subresource_name, is_collection=False):
     """Helper function to find the subresource path
 
     :param resource: ResourceBase instance on which the name
         gets queried upon.
     :param subresource_name: name of the resource field to
         fetch the '@odata.id' from.
+    :param is_collection: if `True`, expect a list of resources to
+        fetch the '@odata.id' from.
+    :returns: Resource path (if `is_collection` is `False`) or
+        a list of resource paths (if `is_collection` is `True`).
     """
     if not subresource_name:
         raise ValueError('"subresource_name" cannot be empty')
@@ -88,12 +92,24 @@ def get_sub_resource_path_by(resource, subresource_name):
         raise exceptions.MissingAttributeError(
             attribute='/'.join(subresource_name), resource=resource.path)
 
-    if '@odata.id' not in body:
-        raise exceptions.MissingAttributeError(
-            attribute='/'.join(subresource_name) + '/@odata.id',
-            resource=resource.path)
+    elements = []
 
-    return body['@odata.id']
+    try:
+        if is_collection:
+            for element in body:
+                elements.append(element['@odata.id'])
+            return elements
+
+        else:
+            return body['@odata.id']
+
+    except (TypeError, KeyError):
+        attribute = '/'.join(subresource_name)
+        if is_collection:
+            attribute += '[%s]' % len(elements)
+        attribute += '/@odata.id'
+        raise exceptions.MissingAttributeError(
+            attribute=attribute, resource=resource.path)
 
 
 def max_safe(iterable, default=0):