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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/db-api.txt | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/docs/db-api.txt b/docs/db-api.txt index 9fc82add4a..9390cb0905 100644 --- a/docs/db-api.txt +++ b/docs/db-api.txt @@ -820,6 +820,34 @@ of the arguments is required, but you should use at least one of them. some database backends, such as some MySQL versions, don't support subqueries. + **New in Django development version** + In some rare cases, you might wish to pass parameters to the SQL fragments + in ``extra(select=...)```. Since the ``params`` attribute is a sequence + and the ``select`` attribute is a dictionary, some care is required so + that the parameters are matched up correctly with the extra select pieces. + Firstly, in this situation, you should use a + ``django.utils.datastructures.SortedDict`` for the ``select`` value, not + just a normal Python dictionary. Secondly, make sure that your parameters + for the ``select`` come first in the list and that you have not passed any + parameters to an earlier ``extra()`` call for this queryset. + + This will work:: + + Blog.objects.extra( + select=SortedDict(('a', '%s'), ('b', '%s')), + params=('one', 'two')) + + ... while this won't:: + + # Will not work! + Blog.objects.extra(where=['foo=%s'], params=('bar',)).extra( + select=SortedDict(('a', '%s'), ('b', '%s')), + params=('one', 'two')) + + In the second example, the earlier ``params`` usage will mess up the later + one. So always put your extra select pieces in the first ``extra()`` call + if you need to use parameters in them. + ``where`` / ``tables`` You can define explicit SQL ``WHERE`` clauses -- perhaps to perform non-explicit joins -- by using ``where``. You can manually add tables to |