I just have a hunch about this. But if feels like I'm doing it the wrong way. What I want to do is to have a db.StringProperty() as a unique identifier. I have a simple db.Model, with property name and file. If I add another entry with the same "name" as one already in the db.Model I want to update this.
As of know I look it up with:
template = Templates.all().filter('name = ', name)
Check if it's one entry already:
if template.count() > 0:
Then add it or update it. But from what I've read .count() is every expensive in CPU usage.
Is there away to set the "name" property to be unique and the datastore will automatic update it or another better way to do this?
..fredrik
You can't make a property unique in the App Engine datastore. What you can do instead is to specify a key name for your model, which is guaranteed to be unique - see the docs for details.
I was having the same problem and came up with the following answer as the simplest one :
class Car(db.Model):
name = db.StringProperty(required=True)
def __init__(self,*args, **kwargs):
super(Car, self).__init__(*args, **kwargs)
loadingAnExistingCar = ("key" in kwargs.keys() or "key_name" in kwargs.keys())
if not loadingAnExistingCar:
self.__makeSureTheCarsNameIsUnique(kwargs['name'])
def __makeSureTheCarsNameIsUnique(self, name):
existingCarWithTheSameName = Car.GetByName(name)
if existingCarWithTheSameName:
raise UniqueConstraintValidationException("Car should be unique by name")
#staticmethod
def GetByName(name):
return Car.all().filter("name", name).get()
It's important to not that I first check if we are loading an existing entity first.
For the complete solution : http://nicholaslemay.blogspot.com/2010/07/app-engine-unique-constraint.html
You can just try to get your entity and edit it, and if not found create a new one:
template = Templates.gql('WHERE name = :1', name)
if template is None:
template = Templates()
# do your thing to set the entity's properties
template.put()
That way it will insert a new entry when it wasn't found, and if it was found it will update the existing entry with the changes you made (see documentation here).
An alternative solution is to create a model to store the unique values, and store it transationally using a combination of Model.property_name.value as key. Only if that value is created you save your actual model. This solution is described (with code) here:
http://squeeville.com/2009/01/30/add-a-unique-constraint-to-google-app-engine/
I agree with Nick. But, if you do ever want to check for model/entity existence based on a property, the get() method is handy:
template = Templates.all().filter('name = ', name).get()
if template is None:
# doesn't exist
else:
# exists
I wrote some code to do this. The idea for it is to be pretty easy to use. So you can do this:
if register_property_value('User', 'username', 'sexy_bbw_vixen'):
return 'Successfully registered sexy_bbw_vixen as your username!'
else:
return 'The username sexy_bbw_vixen is already in use.'
This is the code. There are a lot of comments, but its actually only a few lines:
# This entity type is a registry. It doesn't hold any data, but
# each entity is keyed to an Entity_type-Property_name-Property-value
# this allows for a transaction to 'register' a property value. It returns
# 'False' if the property value is already in use, and thus cannot be used
# again. Or 'True' if the property value was not in use and was successfully
# 'registered'
class M_Property_Value_Register(db.Expando):
pass
# This is the transaction. It returns 'False' if the value is already
# in use, or 'True' if the property value was successfully registered.
def _register_property_value_txn(in_key_name):
entity = M_Property_Value_Register.get_by_key_name(in_key_name)
if entity is not None:
return False
entity = M_Property_Value_Register(key_name=in_key_name)
entity.put()
return True
# This is the function that is called by your code, it constructs a key value
# from your Model-Property-Property-value trio and then runs a transaction
# that attempts to register the new property value. It returns 'True' if the
# value was successfully registered. Or 'False' if the value was already in use.
def register_property_value(model_name, property_name, property_value):
key_name = model_name + '_' + property_name + '_' + property_value
return db.run_in_transaction(_register_property_value_txn, key_name )
Related
I have a simple model:
class Item(models.Model):
user = ForeignKey(User, related_name="user_items")
users = ManyToManyField(User, related_name="users_items")
I want it so that when a user creates an Item via ViewSet, that user is automatically assigned to the user and users fields.
I typically do this for ForeignKey's via the ViewSet's perform_create:
class ItemViewSet(viewsets.ModelViewSet):
...
def perform_create(self, serializer):
if self.request.user.is_authenticated:
serializer.save(user=self.request.user)
else:
serializer.save()
When I try to do it for the ManyToManyField too, I get this error:
{'users': [ErrorDetail(string='This list may not be empty.', code='empty')]}
I've tried the following in perform_create():
# 1
serializer.save(user=self.request.user, users=self.request.user)
# 2
serializer.save(user=self.request.user, users=[self.request.user])
# 2
serializer.save(user=self.request.user, users=[self.request.user.id])
How can I update a ManyToManyField via a ViewSet's perform_create?
Edit:
I guess the following works:
obj = serializer.save(user=self.request.user)
obj.users.add(self.request.user)
Is there no way to have the M2M field when the object is initially created though?
when you want set a list to m2m field one of the things you can do is this:
item_obj.users.set(user_list)
probably you need first get your item_obj.
for this you can get your object id from item_id = serializer.data.get('id') , and then item_obj = Item.objects.get(id = item_id)
I'm using DispensingUnit class name and having two fields 'keypad1_sr_no_hw' and 'keypad2_sr_no_hw'.
How can we compare the uniqueness of these two fields meaning two fields never having same combination ofvalues?
Used this unique_together, but its not working.
class Meta:
unique_together = (("keypad1_sr_no_hw", "keypad2_sr_no_hw",))
class DispensingUnit(models.Model):
keypad1_sr_no_hw = models.CharField(U'Keypad 1', max_length=20 ,)
keypad2_sr_no_hw = models.CharField(U'Keypad 2', max_length=20,)
value in keypad1_sr_no_hw is KP2019310001 and in keypad2_sr_no_hw KP2019310001 and still get saved.
I expect that when both the values are same it will show error and values do not get stored.
Have you tried overriding the save method, do something along the line
def save(self, *args, **kwargs):
if self.keypad1_sr_no_hw == self.keypad2_sr_no_hw:
raise ValidationError("keypad1_sr_no_hw and keypad2_sr_no_hw have same values")
return super(DispensingUnit, self).save(*args, **kwargs)
I know It might not be what you are looking for, but it will do the job for you, I am not sure that any built-in django property exists that can compare multiple fields for Uniqueness.
I'm creating a custom module in odoo and I'm struggling with an inheritance issue, let's say i have the following implementation :
class SuperModel(models.Model) :
_name="model_name"
_inherits={'model_name.one':'model_name_one_id',
'model_name.two':'model_name_two_id'}
selection = fields.Selection(selection=[('m1','Model one'),('m2','Model Two')])
model_name_one_id = fields.Many2one(comodel_name="model_name.one",ondelete="cascade")
model_name_two_id = fields.Many2one(comodel_name="model_name.two",ondelete="cascade")
class ModelOne(models.Model):
_name="model_name.one"
value_one = fields.Char()
class ModelTwo(models.Model):
_name="model_name.two"
value_two = fields.Char()
What i want to achieve, is by selecting "Model 1" or "Model 2" in the main model view, only the corresponding fields will be displayed and stored in the database.
But whenever i create a record for "SuperModel" both records are created in "ModelOne" and "ModelTwo" tables.
For example if i select "Model 1" and fill "value_one", when saving, an empty record is created in "Model 2" table (model_name_two_id == False). How can i prevent that ?
Thank you for helping :)
OK using Delegate is impossible in you condition because odoo will make sure that the
many2one must have a value or the saving will not happen so use related field like this
class SuperModel(models.Model) :
_name="model_name"
selection = fields.Selection(selection=[('m1','Model one'),('m2','Model Two')])
# indecate that the Many2one are delegated = true
model_name_one_id = fields.Many2one(comodel_name="model_name.one",ondelete="cascade", )
model_name_two_id = fields.Many2one(comodel_name="model_name.two",ondelete="cascade", )
value_one = fields.Char(related="model_name_one_id.value_one")
value_two = fields.Char(related="model_name_two_id.value_two")
#api.model
def create(self, vals):
if not rec_id.value_one:
# if the related field of model_name_one_id are no null
# create a record from that relateds fields add it to vals
# i used vals directly odoo is smart to ignore the non existing field in model_name.one
# or iterate the vals and extract a dictionary of model_name.one
m2on_rec = self.env['model_name.one'].create(vals) # create a record
vals.update({'model_name_one_id':m2on_rec.id}) # add the id to vals
return super(SuperModel, self).create(vals)
elif not rec_id.value_one:
# same thing for the second many2one
else :
# show error or create a simple record
return return super(SuperModel, self).create(vals)
#api.one # is used one so i make sure that self containing only one record it's hard for multi need to much code
def write(self, vals):
# check if any of the related field of model_name_one_id is changed
if any(field_name in self.env['model_name.one'] for field_name in vals.keys()) :
# then check the many2one field all ready have a value so the operation here is update
if self.model_name_one_id:
return super(SuperModel, self).write(vals) # related field will do the changes
else :
# here we need to delete the record of model_name_two_id
self.model_name_two_id.unlink()
# here the same thing in create you need to create the record
retrun super(SuperModel, self).write(vals)
else :
# same thing for model_name_two_id
i tried this solution and it work sooo fine just create the record of the one2many field it's like you are the one who are delegating not the frame work for editing is more complex because you need to delete the record and then save the new one
Suppose I have the following Model:
class myClassObj(models.Model):
flag1 = models.NullBooleanField()
flag2 = models.BooleanField()
Now also suppose I want the Database to enforce the following constraint:
flag1 should be None if and only if flag2 is false
How can I write the constraints in this model so that this condition is checked any time a myClassObj is created or edited? I see some interesting information here. But I don't see how to specify an "iff" constraint as I described above.
The Django documentation recommends doing custom validation where access to multiple fields is required by overriding Model.clean().
This example from the documentation show how it's possible to validate that a news article still in the "draft" phase does not have a publication date.
def clean(self):
import datetime
from django.core.exceptions import ValidationError
# Don't allow draft entries to have a pub_date.
if self.status == 'draft' and self.pub_date is not None:
raise ValidationError('Draft entries may not have a publication date.')
# Set the pub_date for published items if it hasn't been set already.
if self.status == 'published' and self.pub_date is None:
self.pub_date = datetime.date.today()
For more detailed information, see the full reference here: https://docs.djangoproject.com/en/dev/ref/models/instances/#validating-objects
To have this called every time you save the object you'll also need to override the save method: https://docs.djangoproject.com/en/dev/topics/db/models/#overriding-model-methods.
Another useful reference for other use cases if you only need to validate a single field is writing custom validators: https://docs.djangoproject.com/en/dev/ref/validators/
django nonrel's documentation states: "you have to manually write code for merging the results of multiple queries (JOINs, select_related(), etc.)".
Can someone point me to any snippets that manually add the related data? #nickjohnson has an excellent post showing how to do this with the straight AppEngine models, but I'm using django-nonrel.
For my particular use I'm trying to get the UserProfiles with their related User models. This should be just two simple queries, then match the data.
However, using django-nonrel, a new query gets fired off for each result in the queryset. How can I get access to the related items in a 'select_related' sort of way?
I've tried this, but it doesn't seem to work as I'd expect. Looking at the rpc stats, it still seems to be firing a query for each item displayed.
all_profiles = UserProfile.objects.all()
user_pks = set()
for profile in all_profiles:
user_pks.add(profile.user_id) # a way to access the pk without triggering the query
users = User.objects.filter(pk__in=user_pks)
for profile in all_profiles:
profile.user = get_matching_model(profile.user_id, users)
def get_matching_model(key, queryset):
"""Generator expression to get the next match for a given key"""
try:
return (model for model in queryset if model.pk == key).next()
except StopIteration:
return None
UPDATE:
Ick... I figured out what my issue was.
I was trying to improve the efficiency of the changelist_view in the django admin. It seemed that the select_related logic above was still producing additional queries for each row in the results set when a foreign key was in my 'display_list'. However, I traced it down to something different. The above logic does not produce multiple queries (but if you more closely mimic Nick Johnson's way it will look a lot prettier).
The issue is that in django.contrib.admin.views.main on line 117 inside the ChangeList method there is the following code: result_list = self.query_set._clone(). So, even though I was properly overriding the queryset in the admin and selecting the related stuff, this method was triggering a clone of the queryset which does NOT keep the attributes on the model that I had added for my 'select related', resulting in an even more inefficient page load than when I started.
Not sure what to do about it yet, but the code that selects related stuff is just fine.
I don't like answering my own question, but the answer might help others.
Here is my solution that will get related items on a queryset based entirely on Nick Johnson's solution linked above.
from collections import defaultdict
def get_with_related(queryset, *attrs):
"""
Adds related attributes to a queryset in a more efficient way
than simply triggering the new query on access at runtime.
attrs must be valid either foreign keys or one to one fields on the queryset model
"""
# Makes a list of the entity and related attribute to grab for all possibilities
fields = [(model, attr) for model in queryset for attr in attrs]
# we'll need to make one query for each related attribute because
# I don't know how to get everything at once. So, we make a list
# of the attribute to fetch and pks to fetch.
ref_keys = defaultdict(list)
for model, attr in fields:
ref_keys[attr].append(get_value_for_datastore(model, attr))
# now make the actual queries for each attribute and store the results
# in a dict of {pk: model} for easy matching later
ref_models = {}
for attr, pk_vals in ref_keys.items():
related_queryset = queryset.model._meta.get_field(attr).rel.to.objects.filter(pk__in=set(pk_vals))
ref_models[attr] = dict((x.pk, x) for x in related_queryset)
# Finally put related items on their models
for model, attr in fields:
setattr(model, attr, ref_models[attr].get(get_value_for_datastore(model, attr)))
return queryset
def get_value_for_datastore(model, attr):
"""
Django's foreign key fields all have attributes 'field_id' where
you can access the pk of the related field without grabbing the
actual value.
"""
return getattr(model, attr + '_id')
To be able to modify the queryset on the admin to make use of the select related we have to jump through a couple hoops. Here is what I've done. The only thing changed on the 'get_results' method of the 'AppEngineRelatedChangeList' is that I removed the self.query_set._clone() and just used self.query_set instead.
class UserProfileAdmin(admin.ModelAdmin):
list_display = ('username', 'user', 'paid')
select_related_fields = ['user']
def get_changelist(self, request, **kwargs):
return AppEngineRelatedChangeList
class AppEngineRelatedChangeList(ChangeList):
def get_query_set(self):
qs = super(AppEngineRelatedChangeList, self).get_query_set()
related_fields = getattr(self.model_admin, 'select_related_fields', [])
return get_with_related(qs, *related_fields)
def get_results(self, request):
paginator = self.model_admin.get_paginator(request, self.query_set, self.list_per_page)
# Get the number of objects, with admin filters applied.
result_count = paginator.count
# Get the total number of objects, with no admin filters applied.
# Perform a slight optimization: Check to see whether any filters were
# given. If not, use paginator.hits to calculate the number of objects,
# because we've already done paginator.hits and the value is cached.
if not self.query_set.query.where:
full_result_count = result_count
else:
full_result_count = self.root_query_set.count()
can_show_all = result_count self.list_per_page
# Get the list of objects to display on this page.
if (self.show_all and can_show_all) or not multi_page:
result_list = self.query_set
else:
try:
result_list = paginator.page(self.page_num+1).object_list
except InvalidPage:
raise IncorrectLookupParameters
self.result_count = result_count
self.full_result_count = full_result_count
self.result_list = result_list
self.can_show_all = can_show_all
self.multi_page = multi_page
self.paginator = paginator