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Diffstat (limited to 'docs/db-api.txt')
| -rw-r--r-- | docs/db-api.txt | 21 |
1 files changed, 16 insertions, 5 deletions
diff --git a/docs/db-api.txt b/docs/db-api.txt index 0d1f049601..2f0c8b0589 100644 --- a/docs/db-api.txt +++ b/docs/db-api.txt @@ -876,15 +876,18 @@ The database API supports the following lookup types: exact ~~~~~ -Exact match. +Exact match. If the value provided for comparison is ``None``, it will +be interpreted as an SQL ``NULL`` (See isnull_ for more details). -Example:: +Examples:: Entry.objects.get(id__exact=14) + Entry.objects.get(id__exact=None) -SQL equivalent:: +SQL equivalents:: SELECT ... WHERE id = 14; + SELECT ... WHERE id = NULL; iexact ~~~~~~ @@ -1103,8 +1106,8 @@ such as January 3, July 3, etc. isnull ~~~~~~ -``NULL`` or ``IS NOT NULL`` match. Takes either ``True`` or ``False``, which -correspond to ``IS NULL`` and ``IS NOT NULL``, respectively. +Takes either ``True`` or ``False``, which correspond to SQL queries of +``IS NULL`` and ``IS NOT NULL``, respectively. Example:: @@ -1114,6 +1117,14 @@ SQL equivalent:: SELECT ... WHERE pub_date IS NULL; +.. admonition:: ``__isnull=True`` vs ``__exact=None`` + + There is an important difference between ``__isnull=True`` and + ``__exact=None``. ``__exact=None`` will *always* return an empty result + set, because SQL requires that no value is equal to ``NULL``. + ``__isnull`` determines if the field is currently holding the value + of ``NULL`` without performing a comparison. + search ~~~~~~ |