Django如何根据相关字段订购对象

Question

The following code is used to determine the order of objects as they get dumped to JSON. It also allows the datatables jquery plug in to set by which column the order is being established, and if its ascending or descending. This works great for the default ordering of objects, but what if I want to order an object based on a related field? How would I do that?

objects = StoreLiquor.objects.filter(storeID=store_id)
keys = ['SPI', 'liquorID']

#sorting
order = dict( enumerate(keys) )
dirs = {'asc': '', 'desc': '-'}
ordering = dirs[request.GET['sSortDir_0']] + order[int(request.GET['iSortCol_0'])]
objects = objects.order_by(ordering)

With this code, it will sort just fine based on the liquourID which is a foreign key. But how could I get it to sort alphabetically based on BrandName , a field in the table that liquourID references?

Answer 1

You can use the same style of syntax as you would with filter to query across relations.

eg

objects = objects.order_by('tablename__BrandName')

Where tablename is the name of the Foreign Key field.

From the Django doc :

To order by a field in a different model, use the same syntax as when you are querying across model relations. That is, the name of the field, followed by a double underscore (__), followed by the name of the field in the new model, and so on for as many models as you want to join.

Edit in response to comment from OP:

Based on your response that you want to sort by both the selected column in Datatables and BrandName , I think you would want to pass both as arguments to order_by (which takes multiple arguments to order by successive columns in SQL ):

objects = objects.order_by(ordering, 'tablename__BrandName')

Or reverse the arguments, depending on which column you want to take precedence.

Answer 2

So I was able to figure it out on my own, how to do this. I'm not sure if its the best solution, but implementing if and then statements does work. since enumerate(keys) assigns an integer to each key in keys , and the request for the pressed column to be sorted also returns an int, I set it to change that order based on if its ascending or descending, and if the second column was pressed.

#sorting
order = dict( enumerate(keys) )
direction = request.GET['sSortDir_0']
column = request.GET['iSortCol_0']
dirs = {'asc': '', 'desc': '-'}
if direction == 'asc' and column == '1':
    ordering = dirs[direction] + order[int(column)]
    objects = objects.order_by('liquorID__BrandName')
elif direction == 'desc' and column == '1':
    ordering = dirs[direction] + order[int(column)]
    objects = objects.order_by('-liquorID__BrandName')
else:
    ordering = dirs[direction] + order[int(column)]
    objects = objects.order_by(ordering)