I have a models with several db fields (field1, field2)
I want to create an unique widget to fill value for field1,field2
Possible solution ?
set my widget on field1, and set HiddenInput for field2. But I don't like so much this solution. Is that correct solution at least ?
Is there some other solutions ? like create 1 FormField that is mapped to 2 DB Fields (Not easy to do that in Django Admin)
I checked several solution for similar needs LatLonField, but in the examples I found, lat and lot are stored in a commaseparatedfield which is not acceptable for me.
Related
Is it possible to prevent multiple querys when i use django ORM ? Example:
product = Product.objects.get(name="Banana")
for provider in product.providers.all():
print provider.name
This code will make 2 SQL querys:
1 - SELECT ••• FROM stock_product WHERE stock_product.name = 'Banana'
2 - SELECT stock_provider.id, stock_provider.name FROM stock_provider INNER JOIN stock_product_reference ON (stock_provider.id = stock_product_reference.provider_id) WHERE stock_product_reference.product_id = 1
I confess, i use Doctrine (PHP) for some projects. With doctrine it's possible to specify joins when retrieve the object (relations are populated in object, so no need to query database again for get attribute relation value).
Is it possible to do the same with Django's ORM ?
PS: I hop my question is comprehensive, english is not my primary language.
In Django 1.4 or later, you can use prefetch_related. It's like select_related but allows M2M relations and such.
product = Product.objects.prefetch_related('providers').get(name="Banana")
You still get two queries, though. From the docs:
prefetch_related, on the other hand, does a separate lookup for each relationship, and does the ‘joining’ in Python.
As for packing this down into a single query, Django won't do it like Doctrine because it doesn't do that much post-processing of the result set (Django would have to remove all the redundant column data, since you'll get a row per provider and each of these rows will have a copy of all of product's fields).
So if you want to pack this down to one query, you're going to have to turn it around and run the query on the Provider table (I'm guessing at your schema):
providers = Provider.objects.filter(product__name="Banana").select_related('product')
This should pack it down to one query, but you won't get a single product ORM object out of it, instead needing to get the product fields via providers[k].product.
You can use prefetch_related, sometimes in combination with select_related, to get all related objects in a single query: https://docs.djangoproject.com/en/1.5/ref/models/querysets/#prefetch-related
I've got 2 existing models that I need to join that are non-relational (no foreign keys). These were written by other developers are cannot be modified by me.
Here's a quick description of them:
Model Process
Field filename
Field path
Field somethingelse
Field bar
Model Service
Field filename
Field path
Field servicename
Field foo
I need to join all instances of these two models on the filename and path columns. I've got existing filters I have to apply to each of them before this join occurs.
Example:
A = Process.objects.filter(somethingelse=231)
B = Service.objects.filter(foo='abc')
result = A.filter(filename=B.filename,path=B.path)
This sucks, but your best bet is to iterate all models of one type, and issue queries to get your joined models for the other type.
The other alternative is to run a raw SQL query to perform these joins, and retrieve the IDs for each model object, and then retrieve each joined pair based on that. More efficient at run time, but it will need to be manually maintained if your schema evolves.
I have a model in my django project called "change" and it has a field called "change_type". There are multiple values within the change_type field to include "move", "new", "edit" and others with new types being added randomly over any given period of time. I am currently using normal django queries to select groups of entries within the change model.
Is there a quick method to determine what unique entries are in the change_type field? Is there a quick method to return a count of each entry type?
After finding the solution, it is really simple.
Change.objects.all().values('change_type').distinct()
Putting it together:
occurrences = {}
change_types = Change.objects.values_list('change_type', flat=True).distinct()
for type in change_types:
occurrences[type] = Change.objects.filter(change_type=type).count()
http://docs.djangoproject.com/en/dev/topics/db/managers/ maybe that will be helpful for You.
This can now be much more effectively implemented using aggregation:
Change.objects.values('change_type').annotate(Count('change_type'))
The output contain change_type__count field for each respective change_type.
after wracking my brain for days, I just hope someone can point me to the right approach.
I have 4 Models: Page, Element, Style and Post.
Here is my simplyfied models.py/admin.py excerpt: http://pastebin.com/uSHrG0p2
In 2 sentences:
A Element references 1 Style and 1 Post (2 FKs).
A Page can reference many Elements, Elements can be referenced by many pages (M2M).
On the admin site for Page instances I included the M2M relation as 'inline'. So that I have multiple rows to select Element-instances.
One row looking like: [My Post A with My Style X][V]
What I want is to replace that one dropdown with 2 dropdowns. One with all instances of Post and one with all instances of Style (creating Element instances in-place). So that one row would look similar to the Element admin site: [My Post A][V] [My Style X][V]
Sounds easy, but I'm just completely lost after reading and experimenting for 2 days with ModelForms, ModelAdmins, Formsets, ... .
Can I do that without custom views/forms within the Django admin functionality?
One of my approaches was to access the Post/Style instances from a PageAdminForm like this, trying to create a form widget manually from it... but failed to do so:
p = Page.objects.get(pk=1)
f = PageAdminForm(instance=p)
f.base_fields['elements'].choices.queryset[0].post
Any advice or hint which way I need to go?
Thank you for your time!
I got exactly what I wanted after removing the M2M field and linking Elements to a Page with a 3rd ForeignKey in Element:
class Element(models.Model):
page = models.ForeignKey(Page)
post = models.ForeignKey(Post)
style = models.ForeignKey(Style)
Actually a non-M2M link makes more sense for my application after all.
Memo to self: Rethink model relations before trying to outsmart Django :-(
I have a Django app that displays a list of rows in a table to the user. Each row maps to an entry in a database. I want to let the user select the rows they would like deleting by adding a checkbox to the end of each row and a delete button ( similar to how gmail lets you delete multiple mail messages). I can't quite figure out how to write the view in terms of finding out which rows were selected and how to map these to the IDs of the entries that need deleting from the database. A simple code snippet showing how to do this would be greatly appreciated.
UPDATE:
I've found this code snippet that I think should do the trick
You can use the CheckboxSelectMultiple widget to auto-generate the corresponding HTML code so you don't have to do it manually.
You can define your form like so:
class UsersForm(forms.Form):
users = forms.MultipleChoiceField(widget=forms.CheckboxSelectMultiple, choices=[QuerySetIterator(Users.objects.all(), "", False)], label="")
Another advantage is that you also get validation for free.
Create a formset and pass can_delete = True to the constructor. Then, in the template,
{{formset}}