#Django Sortable

The objective of django-sortable is to provide a flexible way to handle sorting within a complex Django application.

Like pagination in Django, django-sortable works on a variety of data-types. When possible, an order_by clause will be added to a QuerySet but django-sortable also handles lists or tuples of dictionaries or objects. Support is also available for building the ORDER BY clause of a SQL query.

##Installation

1. Add django-sortable to the INSTALLED_APPS setting in your project's settings.py file:

   INSTALLED_APPS = (
       # …
       'django_sortable',
   )
   

2. Add the request context processor to the TEMPLATE_CONTEXT_PROCESSORS setting. If you don't have these defined in your settings.py file, you'll have to specify the default ones, and add the request processor at the end. (The current defaults are listed in the Django context processor documentation.) This setting will look something like this:

   TEMPLATE_CONTEXT_PROCESSORS = (
       'django.contrib.auth.context_processors.auth',
       'django.core.context_processors.debug',
       'django.core.context_processors.i18n',
       'django.core.context_processors.media',
       'django.core.context_processors.static',
       'django.contrib.messages.context_processors.messages',
   
       # this is the additional requirement… 
       'django.core.context_processors.request', 
   )
   

##Basic Usage

The most basic way to use django-sortable is to pass a QuerySet to the sortable helper and add some simple template tags. Here's an example view and template:

views.py

from django_sortable.helpers import sortable_helper

def books(request):
    book_list = Book.objects.all()
    books = sortable_helper(request, book_list)
  
    # pagination code would go here, after sorting
    # …
  
    return render_to_response('books.html', {'books': books})

books.html

{% load sortable %}

<table>
    <tr>
        {% sortable_header title %}
        {% sortable_header published %}
    </tr>
    {% for book in books %}
    <tr>
        <td>{{ book.title }}</td>
        <td>{{ book.published }}</td>
    </tr>
    {% endfor %}
</table>

##Advanced Usage

If you need more control over the behavior of django-sortable, you can use the Sortable class directly. Here's how you'd do it:

views.py

from django_sortable.sortable import Sortable

def authors(request):

    # we can pass in a list (or tuple) of dictionaries too!
    author_list = Author.objects.values()

    # the 'author' field actually sorts on last_name then first_name
    sortable = Sortable(author_list, (
        ('author', ('last_name', 'first_name')), 
        'birth_date'
    ))
    field_name = request.GET.get('sort', '')
    direction = request.GET.get('dir', 'asc')
    authors = sortable.sorted(field_name, direction)

    # pagination code would go here, after sorting
    # …

    return render_to_response('authors.html', {'authors': authors})

authors.html

{% load sortable %}

<table>
    <tr>
        <th>{% sortable_link author %}</th>
        <th>{% sortable_link birth_date "Birthday" %}</th>
    </tr>
    {% for author in authors %}
    <tr>
        <td>{{ author.full_name }}</td>
        <td>{{ author.birth_date }}</td>
    </tr>
    {% endfor %}
</table>

##Raw SQL Usage

You can use django-sortable with raw SQL queries by asking it for ordering columns. This way you can build the query yourself and append a predicate generated by django-sortable in the ORDER BY clause. Here's an example:

views.py

from django_sortable.sortable import Sortable

def books(request):

    # all we need is an ordering column, don't pass an object list
    sortable = Sortable(None, (('book', 'b.title'),))
    field_name = request.GET.get('sort', '')
    direction = request.GET.get('dir', 'asc')

    # also, you can pass in a default ordering column(s)
    order_col = sortable.sql_predicate(
        field_name=field_name, 
        direction=direction, 
        default=('m.title', 'p.title', '-t.condition')
    )

    sql = '''
        SELECT      
            b.id AS id,
            b.title AS title,
            b.page_count AS num_pages,
            a.full_name AS author,
        FROM 
            book as b, 
            author as a
        WHERE 
            b.page_count > 100 AND
            b.status = %s AND
            b.author_id = a.id
        ORDER BY ''' + order_col
  
    cursor = connection.cursor()
    cursor.execute(sql, ['available',])
    books = dictfetchall(cursor)

    return render_to_response('books.html', {'books': books})

books.html

{% load sortable %}

<table>
    <tr>
        <th>{% sortable_link book "Book" %}</th>
        <th>Author</th>
    </tr>
    {% for book in books %}
    <tr>
        <td>{{ book.title }}</td>
        <td>{{ book.author }}</td>
    </tr>
    {% endfor %}
</table>

##Additional Options

####Defining Ordering Fields

Sometimes the column you sort by is complex—especially if it spans relationships. You can specify sortable fields with custom order fields very easily. Imagine that we want to sort by author in our basic books example. We need to specify ordering fields for all the fields we want to order by, and add an additional string for a special ordering field:

books = sortable_helper(
    request=request, 
    objects=book_list, 
    fields=('title', 'published', ('author', 'author__fullname'), 'page_count')
)

Notice that we have a tuple for the fields argument, and one of the items in the tuple is another tuple. In this inner tuple, the first item is the field name and the second is our special ordering field. When we sort on author, we're actually sorting on author__fullname.

Defining ordering fields has the secondary benefit of locking down which fields are sorted on.

####Specifying a Default Sort Direction

The default sort direction for all fields is ascending. This is probably fine for textual data, but for numbers it's nice to default to largest first. To specify a default sort direction of descending, place a - before the sort column in the sortable header tag. Here's an example:

{% sortable_header -page_count "Number of Pages" %}

This tag generates a table header (with a default direction of descending) like this:

<th class="sort-none"><a href="/books/?sort=page_count&dir=desc" title="Number of Pages">Number of Pages</a></th>

####Sorting on Multiple Database Columns

If you need more control with exactly how sorting happens, you can specify more than one column to sort by. This works with either Query Sets, lists/tuples of dictionaries or lists/tuples of objects.

Lets assume you want to sort by a book's popularity, but you want to make sure that if two or more books have the same popularity, they are then always sorted by title alphabetically ascending (regardless of the popularity sort direction).

books = sortable_helper(
    request=request, 
    objects=book_list, 
    fields=(
        'title', 
        ('popularity', ('popularity', '++title'))
    )
)

Note how the 'popularity' field is specifying two sort columns, and the second column is prepended with a '++'. We've added some syntax for always sorting in a particular direction no matter what direction is passed to django-sortable. Here's a rundown of how that works:

Note that the column_name and +column_name are identical. The latter was added for consistency.

####Setting Custom Classes

Depending on the direction of the sort, a class will be placed on each header or link. The default classes are sort-asc, sort-desc, and sort-none. However, these are fully customizable using your project's settings. In your settings.py file, set these variables:

SORT_ASC_CLASS = 'sort-asc'
SORT_DESC_CLASS = 'sort-desc'
SORT_NONE_CLASS = 'sort-none'

####Rendering Links

If you want to specify a title in the header or link, you can place it in the sortable_header itself. Do it like this:

{% sortable_header page_count "Number of Pages" %}

This tag generates a table header like this:

<th class="sort-asc"><a href="/books/?sort=page_count&dir=asc" title="Number of Pages">Number of Pages</a></th>

You may want to do this to obscure your database column names, but most commonly you probably just want to make your URLs nicer. If you don't want to use table headers, you can get plain links with the sortable_link tag like this:

{% sortable_link page_count "Number of Pages" %}

This tag will generate a link with a class on the anchor instead of the table header:

<a class="sort-asc" href="/books/?sort=page_count&dir=asc" title="Number of Pages">Number of Pages</a>

####Building Arbitrary Sort Links

If your template code is really gnarly, you can build your own sorting links using some special template tags. This method isn't recommended as common practice, but you can use it in a pinch.

Say you want to have a column header link with this markup:

<th colspan="2" class="my-header sort-asc">
    <a href="/" title="Book">
        <span class="book-icon">Book</span>
    </a>
</th>

Obviously neither sortable_header or sortable_link tags will work here, but we can build this by hand using sortable_class and sortable_url tags.

<th colspan="2" class="my-header {% sortable_class book %}">
    <a href="{% sortable_url book %}" title="Book">
        <span class="book-icon">Book</span>
    </a>
</th>

There is a slight maintenance burden here because you'll have to remember to change both the sortable_class and sortable_url tags if you want to update the sort column.