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Django ORM, how to use values() and still work with choicefield?

I am using django v1.10.2
I am trying to create dynamic reports whereby I store fields and conditions and the main ORM model information into database.
My code for the generation of the dynamic report is
class_object = class_for_name("app.models", main_model_name)
results = (class_object.objects.filter(**conditions_dict)
.values(*display_columns)
.order_by(*sort_columns)
[:50])
So main_model_name can be anything.
This works great except that sometimes associated models of the main_model have choicefield.
So for one of the reports main_model is Pallet.
Pallet has many PalletMovement.
My display columns are :serial_number, created_at, pallet_movement__location
The first two columns are fields that belong to Pallet model.
The last one is from PalletMovement
What happens is that PalletMovement model looks like this:
class PalletMovement(models.Model):
pallet = models.ForeignKey(Pallet, related_name='pallet_movements',
verbose_name=_('Pallet'))
WAREHOUSE_CHOICES = (
('AB', 'AB-Delaware'),
('CD', 'CD-Delaware'),
)
location = models.CharField(choices=WAREHOUSE_CHOICES,
max_length=2,
default='AB',
verbose_name=_('Warehouse Location'))
Since the queryset will return me the raw values, how can I make use of the choicefield in PalletMovement model to ensure that the pallet_movement__location gives me the display of AB-Delaware or CD-Delaware?
Bear in mind that the main_model can be anything depending on what I store in the database.
Presumably, I can store more information in the database to help me do the filtering and presentation of data even better.

The values() method returns a dictionary of key-value pairs representing your field name and a corresponding value.
For example:
Model:
class MyModel(models.Model):
name = models.CharField()
surname = models.CharField()
age = models.IntegerField()
...
Query:
result = MyModel.objects.filter(surname='moutafis').values('name', 'surname')
Result:
< Queryset [{'name': 'moutafis', 'surname': 'john'}] >
You can now manipulate this result as you would a normal dictionary:
if main_model_name is 'PalletMovement':
# Make life easier
choices = dict(PalletMovement.WAREHOUSE_CHOICES)
for item in result:
item.update({
pallet_movement__location: verbal_choice.get(
pallet_movement__location, pallet_movement__location)
})
You can even make this into a function for better re-usability:
def verbalize_choices(choices_dict, queryset, search_key):
result = queryset
for item in result:
item.update({ search_key: choices_dict.get(search_key, search_key) })
return result
verbal_result = verbalize_choices(
dict(PalletMovement.WAREHOUSE_CHOICES),
result,
'pallet_movement__location'
)
I suggest the use of the update() and get() methods because they will save you from potential errors, like:
The search_key does not exist in the choice_dict then get() will return the value of the search_key
update() will try to update the given key-value pair if exists, else it will add it to the dictionary.
If the usage of the above will be in the template representation of your data, you can create a custom template filter instead:
#register.filter(name='verbalize_choice')
def choice_to_verbal(choice):
return dict(PalletMovement.WAREHOUSE_CHOICES)[choice]
Have an extra look here: Django: How to access the display value of a ChoiceField in template given the actual value and the choices?

You would use get_foo_display
In your template:
{{ obj.get_location_display }}
or
{{ obj.pallet_movement.get_location_display }}
[Edit:] As pointed out in the comments this will not work when calling values()

an alternative to create a templatetag is :
{{form.choicefield.1}}
This shows the value of the initial data of the foreign key field instead the id.

The universal solution for any main_model_name is by Django Model _meta API introspection: class_object._meta.get_field(field_name).choices
That is:
choice_dicts = {}
for field_name in display_columns:
choice_dicts[field_name] = {
k: v for k, v in class_object._meta.get_field(field_name).choices
}
out = []
for row in results:
out.append({name: choice_dicts[name].get(value, value)
for name, value in row.items()
})
The rest is a trivial example, mostly copied code from the question
>>> pallet = app.models.Pallet.objects.create()
>>> palletm = app.models.PalletMovement.objects.create(pallet=pallet, location='AB')
>>>
>>> main_model_name = 'PalletMovement'
>>> conditions_dict = {}
>>> display_columns = ['pallet_id', 'location']
>>> sort_columns = []
>>>
>>> class_object = class_for_name("app.models", main_model_name)
>>> results = (class_object.objects.filter(**conditions_dict)
... .values(*display_columns)
... .order_by(*sort_columns)
... )[:50]
>>>
>>> # *** INSERT HERE ALL CODE THAT WAS ABOVE ***
>>>
>>> print(out)
[{'location': 'AB-Delaware', 'pallet_id': 1}]
It works equally with 'pallet_id' or with 'pallet' in display_columns. Even that "_meta" starts with underscore, it is a documented API.

Can I lookup a related field using a Q object in the Django ORM?

In Django, can I re-use an existing Q object on multiple models, without writing the same filters twice?
I was thinking about something along the lines of the pseudo-Django code below, but did not find anything relevant in the documentation :
class Author(Model):
name = TextField()
company_name = TextField()
class Book(Model):
author = ForeignKey(Author)
# Create a Q object for the Author model
q_author = Q(company_name="Books & co.")
# Use it to retrieve Book objects
qs = Book.objects.filter(author__matches=q_author)
If that is not possible, can I extend an existing Q object to work on a related field? Pseudo-example :
# q_book == Q(author__company_name="Books & co.")
q_book = q_author.extend("author")
# Use it to retrieve Book objects
qs = Book.objects.filter(q_book)
The only thing I've found that comes close is using a subquery, which is a bit unwieldy :
qs = Book.objects.filter(author__in=Author.objects.filter(q_author))

From what I can tell by your comment, it just looks like you're trying to pass a set of common arguments to multiple filters, to do that you can just unpack a dictionary
The values in the dictionary can still be q objects if required as if it were a value you would pass in to the filter argument normally
args = { 'author__company_name': "Books & co" }
qs = Book.objects.filter(**args)
args['author_name'] = 'Foo'
qs = Book.objects.filter(**args)
To share this between different models, you'd have to do some dictionary mangling
author_args = { k.lstrip('author__'): v for k, v in args.items }

You can do this
books = Book.objects.filter(author__company_name="Books & co")

How to set group = true in couchdb

I am trying to use map/reduce to find the duplication of the data in couchDB
the map function is like this:
function(doc) {
if(doc.coordinates) {
emit({
twitter_id: doc.id_str,
text: doc.text,
coordinates: doc.coordinates
},1)};
}
}
and the reduce function is:
function(keys,values,rereduce){return sum(values)}
I want to find the sum of the data in the same key, but it just add everything together and I get the result:
<Row key=None, value=1035>
Is that a problem of group? How can I set it to true?

Assuming you're using the couchdb package from pypi, you'll need to pass a dictionary with all of the options you require to the view.
for example:
import couchdb
# the design doc and view name of the view you want to use
ddoc = "my_design_document"
view_name = "my_view"
#your server
server = couchdb.server("http://localhost:5984")
db = server["aCouchDatabase"]
#naming convention when passing a ddoc and view to the view method
view_string = ddoc +"/" + view_name
#query options
view_options = {"reduce": True,
"group" : True,
"group_level" : 2}
#call the view
results = db.view(view_string, view_options)
for row in results:
#do something
pass

Query different collection by different variable in mongoengine and Django

Is it possible to use variable as the part of collection name and query different collection based on the name in mongoengine?
For example:
There are 3 collections in my mongoDB
collection_first
collection_second
collection_third
and execute a simple for-loop like:
collection_names = ['first', 'second', 'third']
for name in collection_names:
## Query the collection_+`name` here
By the way, I am using mongoengin in Django, how to set the model.py of this kind of scenario?
class Testing(DynamicDocument):
# The collection_name should be dynamic, isn't it?
meta = {'collection' : 'collection_name'}
user_name = StringField(db_field='user_name')
Thank you very much.
Update the solution.
Define the Model in models.py without meta:
class Testing(DynamicDocument):
## Do NOT use the meta to point to a specific collection.
user_name = StringField(db_field='user_name')
When you call the function, use switch_collection to switch to the real collection:
def search_in_testing(self, name, **kwargs):
with switch_collection(Testing, 'colection_%s' % (name)):
search_results = Testing.objects(**kwargs)
return search_results
In your code, just call the function in for loop:
collection_names = ['first', 'second', 'third']
for name in collection_names:
search_results = search_in_testing(name, name=name)
Reference: switch_collection in mongoengine

Perhaps the following test in this commit would be of help in some way:
def test_dynamic_collection_naming(self)
def create_collection_name(cls):
return "PERSON"
class DynamicPerson(Document):
name = StringField()
age = IntField()
meta = {'collection': create_collection_name}
collection = DynamicPerson._get_collection_name()
self.assertEquals(collection, 'PERSON')
DynamicPerson(name='Test User', age=30).save()
self.assertTrue(collection in self.db.collection_names())

Yes you can do it like this. As an example,
for name in collection_names:
for doc in db[collection_+'name'].find():
print doc
Here db is Database object.

how to pass multiple function parameters in dictionary?

I have this pattern already in use,
but I'm trying now to pass multiple parameters to the function
should I just add another parameter or is there another syntactical piece I'm
missing?
def newChannel(hname, cname):
pass
action = {'newChannel': (newChannel, hname),
'newNetwork': (newNetwork, cname) , 'loginError': (loginError, nName)}
handler, param = action.get(eventType)
handler(param)
How can i pass multiple params though?
like such......
action = { 'newChannel': (newChannel, hname, cname) }
is that correct?
EDIT:
Would this fly?
action = {'newChannelQueueCreated': (newChannelQueueCreated, (channelName, timestamp)), 'login':
(login, networkName), 'pushSceneToChannel': (pushSceneToChannel, channelName),
'channelRemovedFromNetwork': (channelRemovedFromNetwork, (channelName, timestamp))}
print ok
handler, getter = action.get(eventType(ok))
handler(*getter(ok))

Why not use a tuple?
action = {'newChannel': (newChannel, (hname, cname)),
'newNetwork': (newNetwork, (cname,)),
'loginError': (loginError, (nName,))}
handler, params = action.get(eventType)
handler(*params)