BACKWARDS INCOMPATIBLE: Hash instances by object id rather than value

This patch updates our usage of `attr.s` to set `hash=False`, so that we
use id-based hashing instead of value-based hashing.

attrs 17.1.0 changed the default for `hash` to `None`, which makes
objects unhashable.  We set `hash=False` so that we can continue to use
objects as keys in dictionaries, but without attempting to hash by
value.

http://www.attrs.org/en/stable/changelog.html

Author: rouge8

README.rst

@@ -10,8 +10,10 @@ attrs_sqlalchemy
    :alt: CI status
 
 Use the amazing `attrs <https://attrs.readthedocs.io>`_ library to add
-``__repr__``, ``__eq__``, ``__cmp__``, and ``__hash__`` methods according to
-the fields on a SQLAlchemy model class.
+``__repr__``, ``__eq__``, and ``__cmp__`` methods according to the fields on a
+SQLAlchemy model class.
+
+``__hash__`` will always fall back to id-based hashing from ``object``.
 
 
 Example
@@ -47,6 +49,26 @@ Installation
 
    $ pip install attrs_sqlalchemy
 
+Changelog
+=========
+
+0.2.0 (UNRELEASED)
+------------------
+
+- **Backward-incompatible**: Apply ``attr.s`` with ``hash=False``, using
+  id-based hashing instead of value-based hashing.
+
+  attrs 17.0.0 changed the default for ``hash`` to ``None``, which makes
+  objects unhashable. We set ``hash=False`` so that we can continue to use
+  objects as keys in dictionaries, but without attempting to hash by value.
+
+  http://www.attrs.org/en/stable/changelog.html
+
+0.1.0 (2016-09-24)
+------------------
+
+- Initial release
+
 Project Information
 ===================
 

attrs_sqlalchemy.py

@@ -26,9 +26,24 @@
 
 def attrs_sqlalchemy(maybe_cls=None):
     """
-    A class decorator that adds ``__repr__``, ``__eq__``, ``__cmp__``, and
-    ``__hash__`` methods according to the fields defined on the SQLAlchemy
-    model class.
+    A class decorator that adds ``__repr__``, ``__eq__``,  and ``__cmp__``,
+    methods according to the fields defined on the SQLAlchemy model class.
+
+    ``__hash__`` will always fall back to id-based hashing from
+    :class:`object`.
+
+    .. versionchanged:: 0.2.0
+
+       :func:`attr.s` is applied with ``hash=False``, using id-based hashing
+       instead of value-based hashing.
+
+       attrs 17.1.0 changed the default for ``hash`` to ``None``, which makes
+       objects unhashable.
+
+       We set ``hash=False`` so that we can continue to use objects as keys in
+       dictionaries, but without attempting to hash by value.
+
+       http://www.attrs.org/en/stable/changelog.html
     """
     def wrap(cls):
         these = {
@@ -53,7 +68,7 @@ def wrap(cls):
             #   which won't be ready yet.
             for name in inspect(cls).columns.keys()
         }
-        return attr.s(cls, these=these, init=False)
+        return attr.s(cls, these=these, init=False, hash=False)
 
     # `maybe_cls` depends on the usage of the decorator. It's a class if it's
     # used as `@attrs_sqlalchemy` but `None` if it's used as

test_attrs_sqlalchemy.py

@@ -37,9 +37,10 @@ class MyModel(TestBase):
         # Instances should have a repr containing their keys and type
         assert repr(instance) == "MyModel(id=1, text='hello')"
 
-        # Instances should be hashable by their fields and used in a dict
+        # Instances should be hashable by ID, not fields
         d = {instance: True}
-        assert d.get(same_data) == d[instance]
+        assert instance in d
+        assert d.get(same_data) is None
         assert d.get(same_pk) is None
 
     def test_field_name_not_column_name(self):