Make tables context managers

tests/test_wurm.py

@@ -460,3 +460,34 @@ class Test:
     from wurm import typemaps
     assert (list(typemaps.columns_for('field', Test)) ==
             ['field_0', 'field_1'])
+
+
+def test_contextmanager(connection):
+    p = Point(1, 1)
+    p.insert()
+    with p:
+        p.x = 100
+    Point.del_object(p)
+    p, = Point
+    assert p == Point(100, 1)
+
+
+def test_no_contextmanager(connection):
+    p = Point(1, 1)
+    p.insert()
+    p.x = 100
+    Point.del_object(p)
+    p, = Point
+    assert p == Point(1, 1)
+
+
+def test_contextmanager_2(connection):
+    p = Point(1, 1)
+    p.insert()
+    with pytest.raises(KeyboardInterrupt):
+        with p:
+            p.x = 100
+            raise KeyboardInterrupt
+    Point.del_object(p)
+    p, = Point
+    assert p == Point(1, 1)

wurm/tables.py

@@ -245,6 +245,15 @@ def display_owner(self):
     The above will not create a new table, but subclasses of
     ``HasOwner`` will have a field called ``owner`` and a method
     called ``display_owner``.
+
+    Models are context managers, so one could write::
+
+        with MyTable.query(field=value) as obj:
+            obj.field = other_value
+
+    This automatically calls :meth:`commit` on ``obj`` as long as
+    no exception is raised inside the ``with``-block, in which case
+    ``obj`` is left in a dirty state.
     """
     __id_map__: ClassVar[dict]
     __fields_info__: ClassVar[Dict[str, type]]
@@ -305,6 +314,13 @@ def _encode_row(self):
             for column, cooked
             in to_stored(key, ty, getattr(self, key)).items()}
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        if exc_type is None:
+            self.commit()  # FIXME: insert if new?
+
 
 @dataclass
 class WithoutRowid(BaseTable, abstract=True):