Add UnionDict class for lcm

We don't merge common_attrs with node's custom attributes
in deployment info. But YAQL expressions still need to
access 'unified' deployment info, related to node. So
we were merging dicts every time yaql want to access it.
It's a bit slow, so this patch introduces class, which
works like union of several dicts without creation of the new
data structure.

Partial-Bug: #1596987

Change-Id: Iea32ab222421fc7a3c5df66e7e48f4d1a4b931f5

nailgun/nailgun/lcm/context.py

@@ -13,6 +13,7 @@
 #    under the License.
 
 from nailgun import utils
+from nailgun.utils.uniondict import UnionDict
 
 
 class TransactionContext(object):
@@ -29,11 +30,11 @@ class TransactionContext(object):
         self.options = kwargs
 
     def get_new_data(self, node_id):
-        return utils.dict_merge(self.new['common'],
-                                self.new['nodes'][node_id])
+        return UnionDict(self.new['common'],
+                         self.new['nodes'][node_id])
 
     def get_old_data(self, node_id, task_id):
         node_info = utils.get_in(self.old, task_id, 'nodes', node_id)
         if not node_info:
             return {}
-        return utils.dict_merge(self.old[task_id]['common'], node_info)
+        return UnionDict(self.old[task_id]['common'], node_info)

nailgun/nailgun/test/unit/test_uniondict.py

@@ -0,0 +1,105 @@
+#    Copyright 2016 Mirantis, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import yaml
+
+from oslo_serialization import jsonutils
+
+from nailgun.test.base import BaseTestCase
+from nailgun.utils.uniondict import UnionDict
+
+
+class TestUnionDict(BaseTestCase):
+
+    D1 = {'a': 1, 'b': 2, 'c': {'x': 10}}
+    D2 = {'b': 3, 'd': 4, 'c': {'y': 20}}
+    D3 = {'e': 5, 'f': 6, 'c': {'z': 30}}
+    D = {'a': 1, 'b': 3, 'c': {'x': 10, 'y': 20, 'z': 30},
+         'd': 4, 'e': 5, 'f': 6}
+
+    YAML_STR_EXPECTED = """a: 1
+b: 3
+c:
+  x: 10
+  y: 20
+  z: 30
+d: 4
+e: 5
+f: 6"""
+
+    JSON_STR_EXPECTED = ('{"c": {"z": 30, "y": 20, "x": 10}, '
+                         '"b": 3, "a": 1, "f": 6, "e": 5, "d": 4}')
+
+    def test_base(self):
+        d1 = {'a': 1, 'b': 2}
+        d2 = {'c': 3, 'd': 4}
+        d3 = {'e': 5, 'f': 6}
+
+        d = UnionDict(d1, d2, d3)
+        self.assertEqual(d['a'], 1)
+        self.assertEqual(d['b'], 2)
+        self.assertEqual(d['c'], 3)
+        self.assertEqual(d['d'], 4)
+        self.assertEqual(d['e'], 5)
+        self.assertEqual(d['f'], 6)
+        self.assertRaises(KeyError, lambda: d[0])
+
+    def test_override(self):
+        d1 = {'a': 1, 'b': 1}
+        d2 = {'a': 2, 'b': 2}
+        d3 = {'a': 3}
+
+        d = UnionDict(d1, d2, d3)
+        self.assertEqual(d['a'], 3)
+        self.assertEqual(d['b'], 2)
+
+        d = UnionDict(d3, d2, d1)
+        self.assertEqual(d['a'], 1)
+        self.assertEqual(d['b'], 1)
+
+    def test_override_dict(self):
+        d1 = {'a': {'x': 10}}
+        d2 = {'a': 1}
+
+        d = UnionDict(d1, d2)
+        self.assertEqual(d['a'], 1)
+
+        d = UnionDict(d2, d1)
+        self.assertEqual(d['a'], {'x': 10})
+
+    def test_merge(self):
+        d1 = {'a': {'x': 10}}
+        d2 = {'a': {'y': 20}}
+        d3 = {'a': {'z': 30}}
+
+        d = UnionDict(d1, d2, d3)
+        self.assertIsInstance(d['a'], UnionDict)
+        self.assertEqual(d['a']['x'], 10)
+        self.assertEqual(d['a']['y'], 20)
+        self.assertEqual(d['a']['z'], 30)
+
+    def test_yaml_dump(self):
+        d = UnionDict(self.D1, self.D2, self.D3)
+        yaml_str = yaml.dump(d, default_flow_style=False).strip()
+        self.assertEqual(yaml_str, self.YAML_STR_EXPECTED)
+
+    def test_json_dump(self):
+        d = UnionDict(self.D1, self.D2, self.D3)
+        json_str = jsonutils.dumps(d).strip()
+        self.assertEqual(jsonutils.loads(json_str),
+                         jsonutils.loads(self.JSON_STR_EXPECTED))
+
+    def test_repr(self):
+        d = UnionDict(self.D1, self.D2, self.D3)
+        self.assertEquals(eval(repr(d)), self.D)

nailgun/nailgun/utils/uniondict.py

@@ -0,0 +1,71 @@
+#    Copyright 2016 Mirantis, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import collections
+import itertools
+import yaml
+
+
+class UnionDict(collections.Mapping):
+    """Object, which acts like read-only union of several dicts.
+
+    This is an object which acts like a deep merge of several
+    dicts. It's needed to replace real dict, merged with help
+    of utils.dict_merge in LCM code.
+    """
+    def __init__(self, *dicts):
+        for d in dicts:
+            if not isinstance(d, dict):
+                raise ValueError("UnionDict can only be apllied to dicts.")
+
+        self.dicts = list(dicts)
+        self.dicts.reverse()
+        self.keys = set(itertools.chain.from_iterable(dicts))
+
+    def __getitem__(self, key):
+        values = []
+        for d in self.dicts:
+            try:
+                value = d[key]
+            except KeyError:
+                continue
+
+            values.append(value)
+            if not isinstance(value, dict):
+                return values[0]
+
+        if len(values) == 0:
+            raise KeyError(key)
+        elif len(values) == 1:
+            return values[0]
+
+        values.reverse()
+        return UnionDict(*values)
+
+    def __iter__(self):
+        return iter(self.keys)
+
+    def __len__(self):
+        return len(self.keys)
+
+    def __repr__(self):
+        items = ['{!r}: {!r}'.format(k, v) for k, v in self.items()]
+        return '{{{}}}'.format(', '.join(items))
+
+
+def uniondict_representer(dumper, data):
+    return dumper.represent_mapping(u'tag:yaml.org,2002:map', data)
+
+
+yaml.add_representer(UnionDict, uniondict_representer)