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Improved docs/templates.txt section on the 'regroup' tag

git-svn-id: http://code.djangoproject.com/svn/django/trunk@5710 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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commit 0d9f21bb75d6df732d1022ac8928cc181419d202 1 parent 2a500b3
@adrianholovaty adrianholovaty authored
Showing with 72 additions and 22 deletions.
  1. +72 −22 docs/templates.txt
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94 docs/templates.txt
@@ -741,8 +741,19 @@ regroup
Regroup a list of alike objects by a common attribute.
This complex tag is best illustrated by use of an example: say that ``people``
-is a list of ``Person`` objects that have ``first_name``, ``last_name``, and
-``gender`` attributes, and you'd like to display a list that looks like:
+is a list of people represented by dictionaries with ``first_name``,
+``last_name``, and ``gender`` keys::
+
+ people = [
+ {'first_name': 'George', 'last_name': 'Bush', 'gender': 'Male'},
+ {'first_name': 'Bill', 'last_name': 'Clinton', 'gender': 'Male'},
+ {'first_name': 'Margaret', 'last_name': 'Thatcher', 'gender': 'Female'},
+ {'first_name': 'Condoleezza', 'last_name': 'Rice', 'gender': 'Female'},
+ {'first_name': 'Pat', 'last_name': 'Smith', 'gender': 'Unknown'},
+ ]
+
+...and you'd like to display a hierarchical list that is ordered by gender,
+like this:
* Male:
* George Bush
@@ -753,33 +764,72 @@ is a list of ``Person`` objects that have ``first_name``, ``last_name``, and
* Unknown:
* Pat Smith
-The following snippet of template code would accomplish this dubious task::
+You can use the ``{% regroup %}`` tag to group the list of people by gender.
+The following snippet of template code would accomplish this::
+
+ {% regroup people by gender as gender_list %}
- {% regroup people by gender as grouped %}
<ul>
- {% for group in grouped %}
- <li>{{ group.grouper }}
+ {% for gender in gender_list %}
+ <li>{{ gender.grouper }}
<ul>
- {% for item in group.list %}
- <li>{{ item }}</li>
+ {% for item in gender.list %}
+ <li>{{ item.first_name }} {{ item.last_name }}</li>
{% endfor %}
</ul>
</li>
{% endfor %}
</ul>
-As you can see, ``{% regroup %}`` populates a variable with a list of objects
-with ``grouper`` and ``list`` attributes. ``grouper`` contains the item that
-was grouped by; ``list`` contains the list of objects that share that
-``grouper``. In this case, ``grouper`` would be ``Male``, ``Female`` and
-``Unknown``, and ``list`` is the list of people with those genders.
+Let's walk through this example. ``{% regroup %}`` takes three arguments: the
+list you want to regroup, the attribute to group by, and the name of the
+resulting list. Here, we're regrouping the ``people`` list by the ``gender``
+attribute and calling the result ``gender_list``.
+
+``{% regroup %}`` produces a list (in this case, ``gender_list``) of
+**group objects**. Each group object has two attributes:
+
+ * ``grouper`` -- the item that was grouped by (e.g., the string "Male" or
+ "Female").
+ * ``list`` -- a list of all items in this group (e.g., a list of all people
+ with gender='Male').
+
+Note that ``{% regroup %}`` does not order its input! Our example relies on
+the fact that the ``people`` list was ordered by ``gender`` in the first place.
+If the ``people`` list did *not* order its members by ``gender``, the regrouping
+would naively display more than one group for a single gender. For example,
+say the ``people`` list was set to this (note that the males are not grouped
+together)::
+
+ people = [
+ {'first_name': 'Bill', 'last_name': 'Clinton', 'gender': 'Male'},
+ {'first_name': 'Pat', 'last_name': 'Smith', 'gender': 'Unknown'},
+ {'first_name': 'Margaret', 'last_name': 'Thatcher', 'gender': 'Female'},
+ {'first_name': 'George', 'last_name': 'Bush', 'gender': 'Male'},
+ {'first_name': 'Condoleezza', 'last_name': 'Rice', 'gender': 'Female'},
+ ]
+
+With this input for ``people``, the example ``{% regroup %}`` template code
+above would result in the following output:
+
+ * Male:
+ * Bill Clinton
+ * Unknown:
+ * Pat Smith
+ * Female:
+ * Margaret Thatcher
+ * Male:
+ * George Bush
+ * Female:
+ * Condoleezza Rice
+
+The easiest solution to this gotcha is to make sure in your view code that the
+data is ordered according to how you want to display it.
-Note that ``{% regroup %}`` does not work when the list to be grouped is not
-sorted by the key you are grouping by! This means that if your list of people
-was not sorted by gender, you'd need to make sure it is sorted before using it,
-i.e.::
+Another solution is to sort the data in the template using the ``dictsort``
+filter, if your data is in a list of dictionaries::
- {% regroup people|dictsort:"gender" by gender as grouped %}
+ {% regroup people|dictsort:"gender" by gender as gender_list %}
spaceless
~~~~~~~~~
@@ -965,14 +1015,14 @@ If value is ``None``, use given default.
dictsort
~~~~~~~~
-Takes a list of dicts, returns that list sorted by the property given in the
-argument.
+Takes a list of dictionaries, returns that list sorted by the key given in
+the argument.
dictsortreversed
~~~~~~~~~~~~~~~~
-Takes a list of dicts, returns that list sorted in reverse order by the
-property given in the argument.
+Takes a list of dictionaries, returns that list sorted in reverse order by the
+key given in the argument.
divisibleby
~~~~~~~~~~~
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