Develop Reference

Django : Best way to Query a M2M Field , and count occurences

class Edge(BaseInfo):
source = models.ForeignKey('Node', on_delete=models.CASCADE,related_name="is_source")
target = models.ForeignKey('Node', on_delete=models.CASCADE,related_name="is_target")
def __str__(self):
return '%s' % (self.label)
class Meta:
unique_together = ('source','target','label','notes')
class Node(BaseInfo):
item_type_list = [('profile','Profile'),
('page','Page'),
('group','Group'),
('post','Post'),
('phone','Phone'),
('website','Website'),
('email','Email'),
('varia','Varia')
]
item_type = models.CharField(max_length=200,choices=item_type_list,blank = True,null=True)
firstname = models.CharField(max_length=200,blank = True, null=True)
lastname = models.CharField(max_length=200,blank = True,null=True)
identified = models.BooleanField(blank=True,null=True,default=False)
username = models.CharField(max_length=200, blank=True, null=True)
uid = models.CharField(max_length=200,blank=True,null=True)
url = models.CharField(max_length=2000,blank=True,null=True)
edges = models.ManyToManyField('self', through='Edge',blank = True)
I have a Model Node (in this case a soc media profile - item_type) that has relations with other nodes (in this case a post). A profile can be the author of a post. An other profile can like or comment that post.
Question : what is the most efficient way to get all the distinct profiles that liked or commented on anothes profile's post + the count of these likes /comments.
print(Edge.objects.filter(Q(label="Liked")|Q(label="Commented"),q).values("source").annotate(c=Count('source')))
Gets me somewhere but i have the values then (id) and i want to pass the objects to my template rather then .get() all the profiles again...
Result :
Thanks in advance

I ended up with iterating over the queryset and adding the objects that i wanted in a dictionary , if the object was already in dictionary , i would count +1 and add the relation in a nested list.
This doesnt feel right but works for now.
posts = Edge.objects.filter(source = self,target__item_type='post',label='Author')
if posts:
q = Q()
for post in posts:
q = q | Q(target=post.target)
contributors = Edge.objects.filter(Q(label="Liked")|Q(label="Commented"),q)
if contributors:
for i in contributors:
if i.source.uid in results:
if i.label in results[i.source.uid]['relation']:
pass
else:
results[i.source.uid]["relation"].append(i.label)
if 'post' in results[i.source.uid]:
results[i.source.uid]['post'].append(i.target)
else:
results[i.source.uid]['post']=[i.target]
else:
results[i.source.uid] = {'profile' : i.source , 'relation':[i.label],'post':[i.target]}

Can't sort table by model's property (accessor set)

I can't sort table by it's models property. I know that I should set accessor in the column so django-tables2 knows what field to process but it does not work.
This is the table:
class ScansTable(tables.Table):
site = tables.columns.Column(accessor='occurence.site', verbose_name='Site')
url = tables.columns.TemplateColumn("""{{ record.occurence.url|truncatechars:20 }}""",
accessor='occurence.url', verbose_name='Url')
price = tables.columns.TemplateColumn(u"""{{ record.price }} €""")
date = tables.columns.Column(accessor='date',order_by='date')
time = tables.columns.Column(accessor='time',order_by='time')
class Meta:
model = Scan
fields = ('date', 'time', 'site', 'url', 'valid', 'price')
attrs = {'id': 'cans_table',
'class': 'table',}
This is the Scan model:
class Scan(models.Model):
occurence = models.ForeignKey('Occurence', related_name='scans')
datetime = models.DateTimeField()
price = models.DecimalField(max_digits=20,decimal_places=2,null=True,blank=True,verbose_name='Price')
valid = models.BooleanField(default=True,verbose_name='Valid')
def __unicode__(self):
return u'{} {} {} {}'.format(self.occurence, self.datetime, self.price, u'OK' if self.valid else 'NOK')
#property
def date(self):
return self.datetime.date()
#property
def time(self):
return self.datetime.time()
The view:
def scans(request):
...
scans = Scan.objects.filter(occurence__product=product)
scans_table = ScansTable(scans)
RequestConfig(request).configure(scans_table)
scans_table.paginate(page=request.GET.get('page', 1), per_page=50)
return render(request,"dashboard_app/scans.html",context={'scans_table':scans_table})
The table is being properly renderd when I don't want to sort it. When I click on time (for example), it returns:
Cannot resolve keyword u'time' into field. Choices are: datetime,
groups, id, occurence, occurence_id, price, valid
Do you know where is the problem?

it's strange what the type product ?? you show the Occurence model and what value it in the view

It appears that defined properties/methods of the model are not available for sorting/filtering within the queryset. I don't fully understand why that is the case. A solution would be to NOT define date and time as properties on the Scan model, but instead annotate them to the queryset used to populate the data.
from django.db import models
def scans(request):
...
scans = Scan.objects.filter(occurence__product=product).annotate(
date=models.F('datetime__date'),
time=models.F('datetime__time')
)
...
See the documentation here on field lookups. Also you could use the tables specific columns for those fields - note that you don't need to define the accessors now the results are already in the queryset:
class ScansTable(tables.Table):
...
date = tables.DateColumn()
time = tables.TimeColumn()
...

django - can't assign a foreign key

For unknown reasons, I cannot assign a foreign key instance of Item_rarity table into Detailed_item table. Django throws an error:
Cannot assign "u'Basic'": "Detailed_item.rarity" must be a "Item_rarity" instance.
... But in Item_rarity dictionary "Basic" record exists - I can choose it from admin panel and create Detailed_item record manually.
I have defined models:
class Detailed_item(models.Model):
item_id = models.IntegerField(primary_key=True)
name = models.CharField(max_length=50)
level = models.IntegerField()
icon = models.CharField(max_length=150)
rarity = models.ForeignKey('Item_rarity')
general_type = models.ForeignKey('Item_type')
detailed_type = models.ForeignKey('Item_detailed_type')
class Item_rarity(models.Model):
name = models.CharField(max_length=15, primary_key=True)
class Item_type(models.Model):
name = models.CharField(max_length=15, primary_key=True)
class Item_detailed_type(models.Model):
name = models.CharField(max_length=20, primary_key=True)
In views, I try to populate it in this manner (inserting multiple items):
...
items = get_all_items() #get dict of items
for element in items:
tmp_det_type = ''
for key, val in element.iteritems():
#get 'detailed type' from inner dict
if key == "type":
tmp_det_type = val
item = Detailed_item(
item_id=element['id'],
name=element['name'],
level=element['level'],
icon=element['icon'],
rarity=element['rarity'], #error
general_type=element['type'],
detailed_type=tmp_det_type,
)
item.save()
...
I even tried to hard code "Basic" string, but it doesn't work either.
* Solved *
Next two entries, that is Item_type and Item_detailed_type were also invalid.
Correct code:
from app.models import Detailed_item, Item_rarity, Item_type, Item_detailed_type
...
items = get_all_items() #get dict of items
for element in items:
tmp_det_type = ''
for key, val in element.iteritems():
#get 'detailed type' from inner dict
if key == "type":
tmp_det_type = val
#create objects with string values
obj_rarity = Item_rarity(name=element['rarity'])
obj_item_type = Item_type(name=element['type'])
obj_item_detailed_type = Item_detailed_type(name=tmp_det_type)
item = Detailed_item(
item_id=element['id'],
name=element['name'],
level=element['level'],
icon=element['icon'],
rarity=obj_rarity,
general_type=obj_item_type,
detailed_type=obj_item_detailed_type,
)
item.save()
...

Item_rarity instance should be passed while storing Detailed_item object since Item_rarity is a foreign key related object in Detailed_item.
Its that you might have passed the Basic string instead of the <Basic Object> itself.
While creating an object in django using its ORM, any foreign_key related object should be provided with the instance itself instead of the id(pk) of the object, where as while fetching the data from the database you can use either of instance or the id(pk) of the instance.
class ParentModel(models.Model):
model_field = models.CharField(max_length=16)
class MyModel(models.Model):
some_field = models.ForeignKey('ParentModel')
parent_model = ParentModel.objects.create(model_field='some_data')
my_model = MyModel.objects.create(some_field=parent_model)
^^^^^^^^^^^^
Note here that the parent_model object itself is passed instead of the id
While fetching the data back,
parent_model = ParentModel.objects.get(model_field='some_data')
my_model = MyModel.objects.get(some_field=parent_model)
or
my_model = MyModel.objects.get(some_field=parent_model.id)
Both would work in case of data fetch.

You do not have to provide the related object on creation if you change the kwarg in to rarity_name:
item = Detailed_item(
item_id=element['id'],
name=element['name'],
level=element['level'],
icon=element['icon'],
rarity_name=element['rarity'], # no error
general_type=element['type'],
detailed_type=tmp_det_type,
)
I have only tested this with the regular id field (the auto pk) but it
should work with your primary key just fine.
E.g.
class SimpleModel(Model):
value = TextField(blank=True)
class ComplexModel(Model):
simple = ForeingKey(SimpleModel)
title = TextField(unique=True)
ComplexModel.objects.create(title='test', simple_id=1)

I need to query for a set of objects whose primary keys are contained inside of a list

As the title says, I need a way to perform this query. I have tried the following:
user_list_ids = []
user_lists = []
user_entries = OwnerEntry.objects.filter(name=request.user)
for user in user_entries:
user_list_ids.append(user.list_id)
user_lists = ListEntry.objects.filter(id__in=user_list_ids)
for user in user_entries:
user_list_ids.append(user.list_id)
user_lists = ListEntry.objects.filter(id__in=user_list_ids)
However, I get an error on the last line: int() argument must be a string or a number, not 'ListEntry'
Here are the relevant models:
class OwnerEntry(models.Model):
name = models.CharField(max_length=32)
list_id = models.ForeignKey(ListEntry)
class Meta:
ordering = ('name',)
class ListEntry(models.Model):
name = models.CharField(max_length=64)
# active_date = models.DateTimeField('date of last list activity')
expire_date = models.DateField('date of expiration')
create_date = models.DateField('date created')

to answer your question directly, please note that you have a list_id rather than list as a ForeignKey name (OwnerEntry model). In order to actually extract the fk value, you should use list_id_id instead (or rename list_id to list ;))
Please also note that django supports object references, like so:
someowner = OwnerEntry.objects.get( ... )
ownerslist = someowner.listentry_set.all()
cheers!

You can define OwnerEntry's foreign key to ListEntry as :
list_id = models.ForeignKey(ListEntry, related_query_name='owner_entry')
and then do this one-liner in your code:
user_lists = ListEntry.objects.filter(owner_entry__name=request.user)
What this does is exactly filter every ListEntry which has at least one owner_entry whose name is equal to request.user's.
The redefinition of the foreign key is just for the sake of giving a nice name to the query attribute.
For more details on queries that work with backward relationships: https://docs.djangoproject.com/en/dev/topics/db/queries/#lookups-that-span-relationships

Sorting a Django QuerySet by a property (not a field) of the Model

Some code and my goal
My (simplified) model:
class Stop(models.Model):
EXPRESS_STOP = 0
LOCAL_STOP = 1
STOP_TYPES = (
(EXPRESS_STOP, 'Express stop'),
(LOCAL_STOP, 'Local stop'),
)
name = models.CharField(max_length=32)
type = models.PositiveSmallIntegerField(choices=STOP_TYPES)
price = models.DecimalField(max_digits=5, decimal_places=2, null=True, blank=True)
def _get_cost(self):
if self.price == 0:
return 0
elif self.type == self.EXPRESS_STOP:
return self.price / 2
elif self.type == self.LOCAL_STOP:
return self.price * 2
else:
return self.price
cost = property(_get_cost)
My Goal: I want to sort by the cost property. I tried two approaches.
Using order_by QuerySet API
Stops.objects.order_by('cost')
That yielded the following template error:
Caught FieldError while rendering: Cannot resolve keyword 'cost' into field.
Using dictsort template filter
{% with deal_items|dictsort:"cost_estimate" as items_sorted_by_price %}
Received the following template error:
Caught VariableDoesNotExist while rendering: Failed lookup for key [cost] in u'Union Square'
So...
How should I go about doing this?

Use QuerySet.extra() along with CASE ... END to define a new field, and sort on that.
Stops.objects.extra(select={'cost': 'CASE WHEN price=0 THEN 0 '
'WHEN type=:EXPRESS_STOP THEN price/2 WHEN type=:LOCAL_STOP THEN price*2'},
order_by=['cost'])
That, or cast the QuerySet returned from the rest to a list, then use L.sort(key=operator.attrgetter('cost')) on it.