mirror of https://github.com/django/django.git
Fixed #9033 - Add bullets to QuerySet extra() arguments. thanks julien for the suggestion and dwillis for the patch.
git-svn-id: http://code.djangoproject.com/svn/django/trunk@14816 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Timo Graham
parent
76c2c30daf
commit
00f36e0ebf
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@ -709,151 +709,151 @@ principle, so you should avoid them if possible.
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Specify one or more of ``params``, ``select``, ``where`` or ``tables``. None
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of the arguments is required, but you should use at least one of them.
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``select``
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The ``select`` argument lets you put extra fields in the ``SELECT`` clause.
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It should be a dictionary mapping attribute names to SQL clauses to use to
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calculate that attribute.
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* ``select``
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The ``select`` argument lets you put extra fields in the ``SELECT`` clause.
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It should be a dictionary mapping attribute names to SQL clauses to use to
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calculate that attribute.
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Example::
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Example::
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Entry.objects.extra(select={'is_recent': "pub_date > '2006-01-01'"})
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Entry.objects.extra(select={'is_recent': "pub_date > '2006-01-01'"})
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As a result, each ``Entry`` object will have an extra attribute,
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``is_recent``, a boolean representing whether the entry's ``pub_date`` is
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greater than Jan. 1, 2006.
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As a result, each ``Entry`` object will have an extra attribute,
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``is_recent``, a boolean representing whether the entry's ``pub_date`` is
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greater than Jan. 1, 2006.
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Django inserts the given SQL snippet directly into the ``SELECT``
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statement, so the resulting SQL of the above example would be something
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like::
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Django inserts the given SQL snippet directly into the ``SELECT``
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statement, so the resulting SQL of the above example would be something
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like::
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SELECT blog_entry.*, (pub_date > '2006-01-01') AS is_recent
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FROM blog_entry;
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SELECT blog_entry.*, (pub_date > '2006-01-01') AS is_recent
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FROM blog_entry;
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The next example is more advanced; it does a subquery to give each
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resulting ``Blog`` object an ``entry_count`` attribute, an integer count
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of associated ``Entry`` objects::
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The next example is more advanced; it does a subquery to give each
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resulting ``Blog`` object an ``entry_count`` attribute, an integer count
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of associated ``Entry`` objects::
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Blog.objects.extra(
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select={
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'entry_count': 'SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id'
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},
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)
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Blog.objects.extra(
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select={
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'entry_count': 'SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id'
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},
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)
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(In this particular case, we're exploiting the fact that the query will
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already contain the ``blog_blog`` table in its ``FROM`` clause.)
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(In this particular case, we're exploiting the fact that the query will
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already contain the ``blog_blog`` table in its ``FROM`` clause.)
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The resulting SQL of the above example would be::
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The resulting SQL of the above example would be::
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SELECT blog_blog.*, (SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id) AS entry_count
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FROM blog_blog;
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SELECT blog_blog.*, (SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id) AS entry_count
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FROM blog_blog;
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Note that the parenthesis required by most database engines around
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subqueries are not required in Django's ``select`` clauses. Also note that
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some database backends, such as some MySQL versions, don't support
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subqueries.
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Note that the parenthesis required by most database engines around
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subqueries are not required in Django's ``select`` clauses. Also note that
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some database backends, such as some MySQL versions, don't support
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subqueries.
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.. versionadded:: 1.0
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.. versionadded:: 1.0
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In some rare cases, you might wish to pass parameters to the SQL fragments
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in ``extra(select=...)``. For this purpose, use the ``select_params``
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parameter. Since ``select_params`` is a sequence and the ``select``
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attribute is a dictionary, some care is required so that the parameters
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are matched up correctly with the extra select pieces. In this situation,
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you should use a ``django.utils.datastructures.SortedDict`` for the
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``select`` value, not just a normal Python dictionary.
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In some rare cases, you might wish to pass parameters to the SQL fragments
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in ``extra(select=...)``. For this purpose, use the ``select_params``
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parameter. Since ``select_params`` is a sequence and the ``select``
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attribute is a dictionary, some care is required so that the parameters
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are matched up correctly with the extra select pieces. In this situation,
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you should use a ``django.utils.datastructures.SortedDict`` for the
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``select`` value, not just a normal Python dictionary.
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This will work, for example::
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This will work, for example::
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Blog.objects.extra(
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select=SortedDict([('a', '%s'), ('b', '%s')]),
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select_params=('one', 'two'))
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Blog.objects.extra(
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select=SortedDict([('a', '%s'), ('b', '%s')]),
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select_params=('one', 'two'))
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The only thing to be careful about when using select parameters in
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``extra()`` is to avoid using the substring ``"%%s"`` (that's *two*
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percent characters before the ``s``) in the select strings. Django's
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tracking of parameters looks for ``%s`` and an escaped ``%`` character
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like this isn't detected. That will lead to incorrect results.
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The only thing to be careful about when using select parameters in
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``extra()`` is to avoid using the substring ``"%%s"`` (that's *two*
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percent characters before the ``s``) in the select strings. Django's
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tracking of parameters looks for ``%s`` and an escaped ``%`` character
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like this isn't detected. That will lead to incorrect results.
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``where`` / ``tables``
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You can define explicit SQL ``WHERE`` clauses -- perhaps to perform
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non-explicit joins -- by using ``where``. You can manually add tables to
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the SQL ``FROM`` clause by using ``tables``.
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* ``where`` / ``tables``
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You can define explicit SQL ``WHERE`` clauses -- perhaps to perform
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non-explicit joins -- by using ``where``. You can manually add tables to
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the SQL ``FROM`` clause by using ``tables``.
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``where`` and ``tables`` both take a list of strings. All ``where``
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parameters are "AND"ed to any other search criteria.
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``where`` and ``tables`` both take a list of strings. All ``where``
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parameters are "AND"ed to any other search criteria.
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Example::
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Example::
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Entry.objects.extra(where=['id IN (3, 4, 5, 20)'])
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Entry.objects.extra(where=['id IN (3, 4, 5, 20)'])
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...translates (roughly) into the following SQL::
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...translates (roughly) into the following SQL::
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SELECT * FROM blog_entry WHERE id IN (3, 4, 5, 20);
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SELECT * FROM blog_entry WHERE id IN (3, 4, 5, 20);
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Be careful when using the ``tables`` parameter if you're specifying
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tables that are already used in the query. When you add extra tables
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via the ``tables`` parameter, Django assumes you want that table included
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an extra time, if it is already included. That creates a problem,
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since the table name will then be given an alias. If a table appears
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multiple times in an SQL statement, the second and subsequent occurrences
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must use aliases so the database can tell them apart. If you're
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referring to the extra table you added in the extra ``where`` parameter
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this is going to cause errors.
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Be careful when using the ``tables`` parameter if you're specifying
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tables that are already used in the query. When you add extra tables
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via the ``tables`` parameter, Django assumes you want that table included
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an extra time, if it is already included. That creates a problem,
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since the table name will then be given an alias. If a table appears
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multiple times in an SQL statement, the second and subsequent occurrences
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must use aliases so the database can tell them apart. If you're
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referring to the extra table you added in the extra ``where`` parameter
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this is going to cause errors.
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Normally you'll only be adding extra tables that don't already appear in
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the query. However, if the case outlined above does occur, there are a few
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solutions. First, see if you can get by without including the extra table
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and use the one already in the query. If that isn't possible, put your
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``extra()`` call at the front of the queryset construction so that your
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table is the first use of that table. Finally, if all else fails, look at
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the query produced and rewrite your ``where`` addition to use the alias
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given to your extra table. The alias will be the same each time you
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construct the queryset in the same way, so you can rely upon the alias
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name to not change.
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Normally you'll only be adding extra tables that don't already appear in
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the query. However, if the case outlined above does occur, there are a few
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solutions. First, see if you can get by without including the extra table
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and use the one already in the query. If that isn't possible, put your
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``extra()`` call at the front of the queryset construction so that your
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table is the first use of that table. Finally, if all else fails, look at
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the query produced and rewrite your ``where`` addition to use the alias
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given to your extra table. The alias will be the same each time you
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construct the queryset in the same way, so you can rely upon the alias
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name to not change.
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``order_by``
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If you need to order the resulting queryset using some of the new fields
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or tables you have included via ``extra()`` use the ``order_by`` parameter
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to ``extra()`` and pass in a sequence of strings. These strings should
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either be model fields (as in the normal ``order_by()`` method on
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querysets), of the form ``table_name.column_name`` or an alias for a column
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that you specified in the ``select`` parameter to ``extra()``.
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* ``order_by``
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If you need to order the resulting queryset using some of the new fields
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or tables you have included via ``extra()`` use the ``order_by`` parameter
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to ``extra()`` and pass in a sequence of strings. These strings should
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either be model fields (as in the normal ``order_by()`` method on
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querysets), of the form ``table_name.column_name`` or an alias for a column
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that you specified in the ``select`` parameter to ``extra()``.
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For example::
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For example::
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q = Entry.objects.extra(select={'is_recent': "pub_date > '2006-01-01'"})
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q = q.extra(order_by = ['-is_recent'])
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q = Entry.objects.extra(select={'is_recent': "pub_date > '2006-01-01'"})
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q = q.extra(order_by = ['-is_recent'])
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This would sort all the items for which ``is_recent`` is true to the front
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of the result set (``True`` sorts before ``False`` in a descending
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ordering).
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This would sort all the items for which ``is_recent`` is true to the front
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of the result set (``True`` sorts before ``False`` in a descending
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ordering).
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This shows, by the way, that you can make multiple calls to
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``extra()`` and it will behave as you expect (adding new constraints each
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time).
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This shows, by the way, that you can make multiple calls to
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``extra()`` and it will behave as you expect (adding new constraints each
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time).
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``params``
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The ``where`` parameter described above may use standard Python database
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string placeholders -- ``'%s'`` to indicate parameters the database engine
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should automatically quote. The ``params`` argument is a list of any extra
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parameters to be substituted.
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* ``params``
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The ``where`` parameter described above may use standard Python database
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string placeholders -- ``'%s'`` to indicate parameters the database engine
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should automatically quote. The ``params`` argument is a list of any extra
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parameters to be substituted.
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Example::
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Example::
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Entry.objects.extra(where=['headline=%s'], params=['Lennon'])
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Entry.objects.extra(where=['headline=%s'], params=['Lennon'])
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Always use ``params`` instead of embedding values directly into ``where``
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because ``params`` will ensure values are quoted correctly according to
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your particular backend. (For example, quotes will be escaped correctly.)
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Always use ``params`` instead of embedding values directly into ``where``
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because ``params`` will ensure values are quoted correctly according to
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your particular backend. (For example, quotes will be escaped correctly.)
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Bad::
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Bad::
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Entry.objects.extra(where=["headline='Lennon'"])
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Entry.objects.extra(where=["headline='Lennon'"])
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Good::
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Good::
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Entry.objects.extra(where=['headline=%s'], params=['Lennon'])
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Entry.objects.extra(where=['headline=%s'], params=['Lennon'])
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defer
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~~~~~
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