diff options
Diffstat (limited to 'docs/topics')
| -rw-r--r-- | docs/topics/composite-primary-key.txt | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/docs/topics/composite-primary-key.txt b/docs/topics/composite-primary-key.txt index 9e5234ca9f..f252f318c1 100644 --- a/docs/topics/composite-primary-key.txt +++ b/docs/topics/composite-primary-key.txt @@ -131,6 +131,8 @@ database. ``ForeignObject`` is an internal API. This means it is not covered by our :ref:`deprecation policy <internal-release-deprecation-policy>`. +.. _cpk-and-database-functions: + Composite primary keys and database functions ============================================= @@ -141,13 +143,15 @@ Many database functions only accept a single expression. MAX("order_id") -- OK MAX("product_id", "order_id") -- ERROR -As a consequence, they cannot be used with composite primary key references as -they are composed of multiple column expressions. +In these cases, providing a composite primary key reference raises a +``ValueError``, since it is composed of multiple column expressions. An +exception is made for ``Count``. .. code-block:: python Max("order_id") # OK - Max("pk") # ERROR + Max("pk") # ValueError + Count("pk") # OK Composite primary keys in forms =============================== |