Continuation of ndb Property implementation (part 3) (googleapis#6318)

This is still incomplete, it's a very large class.

In particular, this implements:

- Adds `Property._code_name` class and instance attribute
- `Property._fix_up`
- `Property._store_value`
- `Property._set_value`
- `Property._has_value`
- `Property._retrieve_value`
- Modifies `property_clean_cache` fixture to make sure the cache
  is empty on fixture entry and make sure the cache is
  non-empty before clearing

ndb/src/google/cloud/ndb/model.py

@@ -337,6 +337,7 @@ def __hash__(self):
 
 class Property(ModelAttribute):
     # Instance default fallbacks provided by class.
+    _code_name = None
     _name = None
     _indexed = True
     _repeated = False
@@ -746,6 +747,111 @@ def _do_validate(self, value):
 
         return value
 
+    def _fix_up(self, cls, code_name):
+        """Internal helper called to tell the property its name.
+
+        This is called by :meth:`_fix_up_properties`, which is called by
+        :class:`MetaModel` when finishing the construction of a :class:`Model`
+        subclass. The name passed in is the name of the class attribute to
+        which the current property is assigned (a.k.a. the code name). Note
+        that this means that each property instance must be assigned to (at
+        most) one class attribute. E.g. to declare three strings, you must
+        call create three :class`StringProperty` instances:
+
+        .. code-block:: python
+
+            class MyModel(ndb.Model):
+                foo = ndb.StringProperty()
+                bar = ndb.StringProperty()
+                baz = ndb.StringProperty()
+
+        you cannot write:
+
+        .. code-block:: python
+
+            class MyModel(ndb.Model):
+                foo = bar = baz = ndb.StringProperty()
+
+        Args:
+            cls (type): The class that the property is stored on. This argument
+                is unused by this method, but may be used by subclasses.
+            code_name (str): The name (on the class) that refers to this
+                property.
+        """
+        self._code_name = code_name
+        if self._name is None:
+            self._name = code_name
+
+    def _store_value(self, entity, value):
+        """Store a value in an entity for this property.
+
+        This assumes validation has already taken place. For a repeated
+        property the value should be a list.
+
+        Args:
+            entity (Model): An entity to set a value on.
+            value (Any): The value to be stored for this property.
+        """
+        entity._values[self._name] = value
+
+    def _set_value(self, entity, value):
+        """Set a value in an entity for a property.
+
+        This performs validation first. For a repeated property the value
+        should be a list (or similar container).
+
+        Args:
+            entity (Model): An entity to set a value on.
+            value (Any): The value to be stored for this property.
+
+        Raises:
+            ReadonlyPropertyError: If the ``entity`` is the result of a
+                projection query.
+            .BadValueError: If the current property is repeated but the
+                ``value`` is not a basic container (:class:`list`,
+                :class:`tuple`, :class:`set` or :class:`frozenset`).
+        """
+        if entity._projection:
+            raise ReadonlyPropertyError(
+                "You cannot set property values of a projection entity"
+            )
+
+        if self._repeated:
+            if not isinstance(value, (list, tuple, set, frozenset)):
+                raise exceptions.BadValueError(
+                    "Expected list or tuple, got {!r}".format(value)
+                )
+            value = [self._do_validate(v) for v in value]
+        else:
+            if value is not None:
+                value = self._do_validate(value)
+
+        self._store_value(entity, value)
+
+    def _has_value(self, entity, unused_rest=None):
+        """Determine if the entity has a value for this property.
+
+        Args:
+            entity (Model): An entity to check if the current property has
+                a value set.
+            unused_rest (None): An always unused keyword.
+        """
+        return self._name in entity._values
+
+    def _retrieve_value(self, entity, default=None):
+        """Retrieve the value for this property from an entity.
+
+        This returns :data:`None` if no value is set, or the ``default``
+        argument if given. For a repeated property this returns a list if a
+        value is set, otherwise :data:`None`. No additional transformations
+        are applied.
+
+        Args:
+            entity (Model): An entity to get a value from.
+            default (Optional[Any]): The default value to use as fallback.
+        """
+        return entity._values.get(self._name, default)
+
     def _call_to_base_type(self, value):
         """Call all ``_validate()`` and ``_to_base_type()`` methods on value.
 

ndb/tests/conftest.py

@@ -30,7 +30,9 @@ def property_clean_cache():
     This property is set at runtime (with calls to ``_find_methods()``), so
     this fixture allows resetting the class to its original state.
     """
+    assert model.Property._FIND_METHODS_CACHE == {}
     try:
         yield
     finally:
+        assert model.Property._FIND_METHODS_CACHE != {}
         model.Property._FIND_METHODS_CACHE.clear()

ndb/tests/unit/test_model.py

@@ -645,6 +645,111 @@ def _validate(self, value):
         assert result is value
         assert value == ["SimpleProperty._validate"]
 
+    @staticmethod
+    def test__fix_up():
+        prop = model.Property(name="foo")
+        assert prop._code_name is None
+        prop._fix_up(None, "bar")
+        assert prop._code_name == "bar"
+
+    @staticmethod
+    def test__fix_up_no_name():
+        prop = model.Property()
+        assert prop._name is None
+        assert prop._code_name is None
+
+        prop._fix_up(None, "both")
+        assert prop._code_name == "both"
+        assert prop._name == "both"
+
+    @staticmethod
+    def test__store_value():
+        entity = unittest.mock.Mock(_values={}, spec=("_values",))
+        prop = model.Property(name="foo")
+        prop._store_value(entity, unittest.mock.sentinel.value)
+        assert entity._values == {prop._name: unittest.mock.sentinel.value}
+
+    @staticmethod
+    def test__set_value(property_clean_cache):
+        entity = unittest.mock.Mock(
+            _projection=False,
+            _values={},
+            spec=("_projection", "_values"),
+        )
+        prop = model.Property(name="foo", repeated=False)
+        prop._set_value(entity, 19)
+        assert entity._values == {prop._name: 19}
+
+    @staticmethod
+    def test__set_value_none():
+        entity = unittest.mock.Mock(
+            _projection=False,
+            _values={},
+            spec=("_projection", "_values"),
+        )
+        prop = model.Property(name="foo", repeated=False)
+        prop._set_value(entity, None)
+        assert entity._values == {prop._name: None}
+        # Cache is untouched.
+        assert model.Property._FIND_METHODS_CACHE == {}
+
+    @staticmethod
+    def test__set_value_repeated(property_clean_cache):
+        entity = unittest.mock.Mock(
+            _projection=False,
+            _values={},
+            spec=("_projection", "_values"),
+        )
+        prop = model.Property(name="foo", repeated=True)
+        prop._set_value(entity, (11, 12, 13))
+        assert entity._values == {prop._name: [11, 12, 13]}
+
+    @staticmethod
+    def test__set_value_repeated_bad_container():
+        entity = unittest.mock.Mock(
+            _projection=False,
+            _values={},
+            spec=("_projection", "_values"),
+        )
+        prop = model.Property(name="foo", repeated=True)
+        with pytest.raises(exceptions.BadValueError):
+            prop._set_value(entity, None)
+        # Cache is untouched.
+        assert model.Property._FIND_METHODS_CACHE == {}
+
+    @staticmethod
+    def test__set_value_projection():
+        entity = unittest.mock.Mock(
+            _projection=True,
+            spec=("_projection",),
+        )
+        prop = model.Property(name="foo", repeated=True)
+        with pytest.raises(model.ReadonlyPropertyError):
+            prop._set_value(entity, None)
+        # Cache is untouched.
+        assert model.Property._FIND_METHODS_CACHE == {}
+
+    @staticmethod
+    def test__has_value():
+        prop = model.Property(name="foo")
+        values = {prop._name: 88}
+        entity1 = unittest.mock.Mock(_values=values, spec=("_values",))
+        entity2 = unittest.mock.Mock(_values={}, spec=("_values",))
+
+        assert prop._has_value(entity1)
+        assert not prop._has_value(entity2)
+
+    @staticmethod
+    def test__retrieve_value():
+        prop = model.Property(name="foo")
+        values = {prop._name: b"\x00\x01"}
+        entity1 = unittest.mock.Mock(_values=values, spec=("_values",))
+        entity2 = unittest.mock.Mock(_values={}, spec=("_values",))
+
+        assert prop._retrieve_value(entity1) == b"\x00\x01"
+        assert prop._retrieve_value(entity2) is None
+        assert prop._retrieve_value(entity2, default=b"zip") == b"zip"
+
     @staticmethod
     def _property_subtype_chain():
         class A(model.Property):