  * If the object's primary key attribute is *not* set or if the ``UPDATE``
    didn't update anything, Django executes an ``INSERT``.
  
  .. versionchanged:: 1.6
    Previously Django used ``SELECT`` - if not found ``INSERT`` else ``UPDATE``
    algorithm. The old algorithm resulted in one more query in ``UPDATE`` case.
  
  The one gotcha here is that you should be careful not to specify a primary-key
  value explicitly when saving new objects, if you cannot guarantee the
  primary-key value is unused. For more on this nuance, see `Explicitly specifying
  auto-primary-key values`_ above and `Forcing an INSERT or UPDATE`_ below.
 
</s> remove     The current value of the field will be displayed as a clickable link above the
    input widget.
 </s> add         The current value of the field will be displayed as a clickable link above the
        input widget. </s> remove         Historically, this parameter was only called ``mimetype`` (now
        deprecated), but since this is actually the value included in the HTTP
        ``Content-Type`` header, it can also include the character set
        encoding, which makes it more than just a MIME type specification. If
        ``mimetype`` is specified (not ``None``), that value is used.
        Otherwise, ``content_type`` is used. If neither is given,
        :setting:`DEFAULT_CONTENT_TYPE` is used.
 </s> add             Historically, this parameter was only called ``mimetype`` (now
            deprecated), but since this is actually the value included in the HTTP
            ``Content-Type`` header, it can also include the character set
            encoding, which makes it more than just a MIME type specification. If
            ``mimetype`` is specified (not ``None``), that value is used.
            Otherwise, ``content_type`` is used. If neither is given,
            :setting:`DEFAULT_CONTENT_TYPE` is used. </s> remove     .. versionadded:: 1.5
 </s> add     .. versionchanged:: 1.5

        Keyword arguments were added in Django 1.5. </s> remove In previous versions of Django, the ``pk`` attribute had to be present
on the serialized data or a ``DeserializationError`` would be raised.
 </s> add     In previous versions of Django, the ``pk`` attribute had to be present
    on the serialized data or a ``DeserializationError`` would be raised. </s> remove Some fields in a model won't be deferred, even if you ask for them. You can
never defer the loading of the primary key. If you are using
:meth:`select_related()` to retrieve related models, you shouldn't defer the
loading of the field that connects from the primary model to the related
one, doing so will result in an error.
 </s> add     Some fields in a model won't be deferred, even if you ask for them. You can
    never defer the loading of the primary key. If you are using
    :meth:`select_related()` to retrieve related models, you shouldn't defer the
    loading of the field that connects from the primary model to the related
    one, doing so will result in an error.
    Previously Django used ``SELECT`` - if not found ``INSERT`` else ``UPDATE``
    algorithm. The old algorithm resulted in one more query in ``UPDATE`` case.
  * If the object's primary key attribute is *not* set or if the ``UPDATE``
    didn't update anything, Django executes an ``INSERT``.
  
  .. versionchanged:: 1.6
    Previously Django used ``SELECT`` - if not found ``INSERT`` else ``UPDATE``
    algorithm. The old algorithm resulted in one more query in ``UPDATE`` case.
    Previously Django used ``SELECT`` - if not found ``INSERT`` else ``UPDATE``
    algorithm. The old algorithm resulted in one more query in ``UPDATE`` case.
  
  The one gotcha here is that you should be careful not to specify a primary-key
  value explicitly when saving new objects, if you cannot guarantee the
  primary-key value is unused. For more on this nuance, see `Explicitly specifying
  auto-primary-key values`_ above and `Forcing an INSERT or UPDATE`_ below.
keep keep keep keep replace replace keep keep keep keep keep
 Adapted uses of versionchanged/versionadded to the new form.

Refs #20104. 
docs/ref/models/instances.txt