Add DictionaryField class to resource base

Add `DictionaryField` class capable of handling dictionaries in
resource body JSON.
This is necessary to be able to parse resources like Message
Registry:
"Messages": {
        "Success": {
            "Message": "Completed successfully",
            "Severity": "OK",
            [...]
        },
        "Failure": {
            "Message": "Failed",
            "Severity": "Critical",
            [...]
        }
}

Story: 2001791
Task: 23226
Change-Id: I8a0b6fe2dda4c244be4b7a0abaf601f533dd30f9

sushy/resources/base.py

@@ -187,6 +187,39 @@ class ListField(Field):
         return instances
 
 
+class DictionaryField(Field):
+    """Base class for fields consisting of dictionary of several sub-fields."""
+
+    def __init__(self, *args, **kwargs):
+        super(DictionaryField, self).__init__(*args, **kwargs)
+        self._subfields = dict(_collect_fields(self))
+
+    def _load(self, body, resource, nested_in=None):
+        """Load the dictionary.
+
+        :param body: parent JSON body.
+        :param resource: parent resource.
+        :param nested_in: parent resource name (for error reporting only).
+        :returns: a new dictionary object containing subfields.
+        """
+        nested_in = (nested_in or []) + self._path
+        values = super(DictionaryField, self)._load(body, resource)
+        if values is None:
+            return None
+
+        instances = {}
+        for key, value in values.items():
+            instance_value = copy.copy(self)
+            for attr, field in self._subfields.items():
+                # Hide the Field object behind the real value
+                setattr(instance_value, attr, field._load(value,
+                                                          resource,
+                                                          nested_in))
+            instances[key] = instance_value
+
+        return instances
+
+
 class MappedField(Field):
     """Field taking real value from a mapping."""
 

sushy/tests/unit/resources/test_base.py

@@ -165,7 +165,11 @@ TEST_JSON = {
             'String': 'a fourth string',
             'Integer': 2
         }
-    ]
+    ],
+    'Dictionary': {
+        'key1': {'property_a': 'value1', 'property_b': 'value2'},
+        'key2': {'property_a': 'value3', 'property_b': 'value4'}
+    }
 }
 
 
@@ -187,11 +191,17 @@ class TestListField(resource_base.ListField):
     integer = resource_base.Field('Integer', adapter=int)
 
 
+class TestDictionaryField(resource_base.DictionaryField):
+    property_a = resource_base.Field('property_a')
+    property_b = resource_base.Field('property_b')
+
+
 class ComplexResource(resource_base.ResourceBase):
     string = resource_base.Field('String', required=True)
     integer = resource_base.Field('Integer', adapter=int)
     nested = NestedTestField('Nested')
     field_list = TestListField('ListField')
+    dictionary = TestDictionaryField('Dictionary')
     non_existing_nested = NestedTestField('NonExistingNested')
     non_existing_mapped = resource_base.MappedField('NonExistingMapped',
                                                     MAPPING)
@@ -217,6 +227,11 @@ class FieldTestCase(base.TestCase):
         self.assertEqual('a third string',
                          self.test_resource.field_list[0].string)
         self.assertEqual(2, self.test_resource.field_list[1].integer)
+        self.assertEqual(2, len(self.test_resource.dictionary))
+        self.assertEqual('value1',
+                         self.test_resource.dictionary['key1'].property_a)
+        self.assertEqual('value4',
+                         self.test_resource.dictionary['key2'].property_b)
         self.assertIsNone(self.test_resource.non_existing_nested)
         self.assertIsNone(self.test_resource.non_existing_mapped)