#88 Support the addition of new fields to an existing schema.

- Especially ListFields and DictFields
djc · JonathanWylie · Mar 15, 2016 · Mar 16, 2016 · Mar 16, 2016 · Mar 16, 2016
commit 26b34d36fa14379a2d57c1bbc5fa4468723274ac
diff --git a/couchdb/mapping.py b/couchdb/mapping.py
@@ -177,7 +177,34 @@ def build(cls, **d):
 
     @classmethod
     def wrap(cls, data):
-        instance = cls()
+        """ Wrap the data object with cls, so that any data changes are made to
+        the data object
+
+        cls may define schema for data that is not in data yet,
+            eg a document is saved to the DB
+            the document schema is changed to contain another kind of data
+            load the old document with the new schema
+            we want to be able to
+                write the data for the new schema
+                get a default value for the new schema
+
+        :param data: A dictionary object of data
+        :return: an instance of class which provides a nice interface to the
+            information in the data object
+        """
+
+        # Build the instance, this means defaults are set for any new fields
+        instance = cls(**data)
+        # instance now has a _data it's own data object which has been created
+        # based on data, and any new schema which may not have been in
+        # the original doc
+
+        # We have to wrap the data object, but we don't want to loose the
+        # defaults created in instance._data
+        # Merge any changes of data from instance back into the main data object
+        data.update(instance._data)
+
+        # make the instance wrap the data object
         instance._data = data
         return instance
 

diff --git a/couchdb/tests/mapping.py b/couchdb/tests/mapping.py
@@ -6,6 +6,7 @@
 # This software is licensed as described in the file COPYING, which
 # you should have received as part of this distribution.
 
+import copy
 from decimal import Decimal
 import unittest
 
@@ -250,6 +251,86 @@ def test_query(self):
         self.assertEqual(type(results.rows[0]), self.Item)
 
 
+class TestWrap(testutil.TempDatabaseMixin, unittest.TestCase):
+
+    def test_simple_schema_change(self):
+        my_mapping = mapping.Mapping.build(
+            name=mapping.TextField(),
+        )
+        my_instance = my_mapping.wrap({})
+        my_instance.name = 'Harry'
+
+        data = copy.copy(my_instance._data)
+
+        my_new_mapping = mapping.Mapping.build(
+            name=mapping.TextField(),
+            age=mapping.IntegerField(),
+        )
+
+        instance = my_new_mapping.wrap(data)
+        instance.age = 32
+        assert data['age'] == 32
+
+    def test_defaults_for_new_schema_should_be_set(self):
+        my_mapping = mapping.Mapping.build(
+            name=mapping.TextField(),
+        )
+        my_instance = my_mapping.wrap({})
+        my_instance.name = 'Harry'
+
+        data = copy.copy(my_instance._data)
+
+        my_new_mapping = mapping.Mapping.build(
+            name=mapping.TextField(),
+            address=mapping.DictField(mapping.Mapping.build(
+                number=mapping.IntegerField(default=1),
+                street=mapping.TextField(default='street')
+            )),
+            pets=mapping.ListField(mapping.TextField(), default=[])
+        )
+
+        my_new_instance = my_new_mapping.wrap(data)
+
+        assert data['pets'] == []
+        assert data['address']['number'] == 1
+        assert data['address']['street'] == 'street'
+        assert my_new_instance.address.number == 1
+        assert my_new_instance.address.street == 'street'
+
+    def test_can_set_new_schema_data(self):
+        my_mapping = mapping.Mapping.build(
+            name=mapping.TextField(),
+        )
+        my_instance = my_mapping.wrap({})
+        my_instance.name = 'Sherlock'
+
+        data = copy.copy(my_instance._data)
+
+        my_new_mapping = mapping.Mapping.build(
+            name=mapping.TextField(),
+            address=mapping.DictField(mapping.Mapping.build(
+                number=mapping.TextField(),
+                street=mapping.TextField()
+            )),
+            pets=mapping.ListField(mapping.TextField(), default=[]),
+        )
+
+        my_new_instance = my_new_mapping.wrap(data)
+
+        my_new_instance.pets.append('dog')
+        my_new_instance.pets.append('cat')
+        my_new_instance.address.number = '221B'
+        my_new_instance.address.street = 'Baker Street'
+
+        assert data['address']['number'] == '221B'
+        assert data['address']['street'] == 'Baker Street'
+        assert data['pets'] == ['dog', 'cat']
+        assert my_new_instance.address.number == '221B'
+        assert my_new_instance.address.street == 'Baker Street'
+        assert my_new_instance.pets[0] == 'dog'
+        assert my_new_instance.pets[1] == 'cat'
+
+
 def suite():
     suite = unittest.TestSuite()
     suite.addTest(testutil.doctest_suite(mapping))