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  • Accessing updated M2M fields in overriden save() in django's admin

    - by Jonathan
    I'd like to use the user updated values of a ManyToManyField in a model's overriden save() method when I save an instance in admin. It turns out that by design, django does not update the M2M field before calling save(), but only after the save() is complete as part of the form save... How can I access the new values of this field in the override save() ?

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  • Alternate datasource for django model?

    - by slypete
    I'm trying to seamlessly integrate some legacy data into a django application. I would like to know if it's possible to use an alternate datasource for a django model. For example, can I contact a server to populate a list of a model? The server would not be SQL based at all. Instead it uses some proprietary tcp based protocol. Copying the data is not an option, as the legacy application will continue to be used for some time. Would a custom manager allow me to do this? This model should behave just like any other django model. It should even pluggable to the admin interface. What do you think? Thanks, Pete

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  • Django comparing model instances for equality

    - by orokusaki
    I understand that, with a singleton situation, you can perform such an operation as: spam == eggs and if spam and eggs are instances of the same class with all the same attribute values, it will return True. In a Django model, this is natural because two separate instances of a model won't ever be the same unless they have the same .pk value. The problem with this is that if a reference to an instance has attributes that have been updated by middleware somewhere along the way and it hasn't been saved, and you're trying to it to another variable holding a reference to an instance of the same model, it will return False of course because they have different values for some of the attributes. Obviously I don't need something like a singleton , but I'm wondering if there some official Djangonic (ha, a new word) method for checking this, or if I should simply check that the .pk value is the same with: spam.pk == eggs.pk I'm sorry if this was a huge waste of time, but it just seems like there might be a method for doing this, and something I'm missing that I'll regret down the road if I don't find it.

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  • Django database caching

    - by hekevintran
    The object user has a foreign key relationship to address. Is there a difference between samples 1 and 2? Does sample 1 run the query multiple times? Or is the address object cached? # Sample 1 country = user.address.country city = user.address.city state = user.address.state # Sample 2 address = user.address country = address.country city = address.city state = address.state

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  • raw_id_fields for modelforms

    - by nbv4
    I have a modelform which has one field that is a ForeignKey value to a model which as 40,000 rows. The default modelform tries to create a select box with 40,000 options, which, to say the least is not ideal. Even more so when this modelform is used in a formset factory! In the admin, this is easiely avoidable by using "raw_id_fields", but there doesn't seem to be a modelform equivalent. How can I do this? Here is my modelform: class OpBaseForm(ModelForm): base = forms.CharField() class Meta: model = OpBase exclude = ['operation', 'routes'] extra = 0 raw_id_fields = ('base', ) #does nothing The first bolded line works by not creating the huge unwieldy selectbox, but when I try to save a fieldset of this form, I get the error: "OpBase.base" must be a "Base" instance. In order for the modelform to be saved, 'base' needs to be a Base instance. Apparently, a string representation of a Base primary key isn't enough (at least not automatically). I need some kind of mechanism to change the string that is given my the form, to a Base instance. And this mechanism has to work in a formset. Any ideas? If only raw_id_fields would work, this would be easy as cake. But as far as I can tell, it only is available in the admin.

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  • Django - Threading in views without hanging the server

    - by bobthabuilda
    One of my applications in my Django project require each request/visitor to that instance to have their own thread. This might sound confusing, so I'll describe what I'm looking to accomplish in a case based scenario, with steps: User visits application Thread starts Until the thread finishes, that user's server instance hangs Once the thread completes, a response is delivered to the user Other visitors to the site should not be affected by any other users using the application How can I accomplish something like this? If possible, I'd like to find a lightweight solution.

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  • Can I filter a django model with a python list?

    - by Rhubarb
    Say I have a model object 'Person' defined, which has a field called 'Name'. And I have a list of people: l = ['Bob','Dave','Jane'] I would like to return a list of all Person records where the first name is not in the list of names defined in l. What is the most pythonic way of doing this?

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  • Reinforcement learning And POMDP

    - by Betamoo
    I am trying to use Multi-Layer NN to implement probability function in Partially Observable Markov Process.. I thought inputs to the NN would be: current state, selected action, result state; The output is a probability in [0,1] (prob. that performing selected action on current state will lead to result state) In training, I fed the inputs stated before, into the NN, and I taught it the output=1.0 for each case that already occurred. The problem : For nearly all test case the output probability is near 0.95.. no output was under 0.9 ! Even for nearly impossible results, it gave that high prob. PS:I think this is because I taught it happened cases only, but not un-happened ones.. But I can not at each step in the episode teach it the output=0.0 for every un-happened action! Any suggestions how to over come this problem? Or may be another way to use NN or to implement prob function? Thanks

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  • Update Rule in Temporal difference

    - by Betamoo
    The update rule TD(0) Q-Learning: Q(t-1) = (1-alpha) * Q(t-1) + (alpha) * (Reward(t-1) + gamma* Max( Q(t) ) ) Then take either the current best action (to optimize) or a random action (to explorer) Where MaxNextQ is the maximum Q that can be got in the next state... But in TD(1) I think update rule will be: Q(t-2) = (1-alpha) * Q(t-2) + (alpha) * (Reward(t-2) + gamma * Reward(t-1) + gamma * gamma * Max( Q(t) ) ) My question: The term gamma * Reward(t-1) means that I will always take my best action at t-1 .. which I think will prevent exploring.. Can someone give me a hint? Thanks

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  • In Rails, how should I implement a Status field for a Tasks app - integer or enum?

    - by Doug
    For a Rails 3.0 Todo app, I have a Tasks model with a Status field. What's the best way to store the Status field data (field type) and still display a human-readable version in a view (HTML table)? Status can be: 0 = Normal 1 = Active 2 = Completed Right now I have this: Rails Schema Here: create_table "tasks", :force = true do |t| t.integer "status", :limit = 1, :default = 0, :null = false Rails Model Here: class Task < ActiveRecord::Base validates_inclusion_of :status, :in => 0..2, :message => "{{value}} must be 0, 1, or 2" Rails View Here: <h1>Listing tasks</h1> <table> <tr> <th>Status</th> <th>Name</th> <th></th> <th></th> <th></th> </tr> <% @tasks.each do |task| %> <tr> <td><%= task.status %></td> <td><%= task.name %></td> <td><%= link_to 'Show', task %></td> <td><%= link_to 'Edit', edit_task_path(task) %></td> <td><%= link_to 'Delete', task, :confirm => 'Are you sure?', :method => :delete %></td> </tr> <% end %> </table> Requirements Store a Task's status in the db such that the values are easily localizable, i.e. I'm not sure I want to store "normal", "active", "completed" as a string field. Solution must work with Rails 3.0. Questions: Should I store the field as an integer (see above)? If so, how do I display the correct human readable status in an HTML table in my Rails view, e.g. show "Active" instead of "1" in the HTML table. Should I use an enum? If so, is this easy to localize later? Should I use straight strings, e.g. "Normal", "Active", "Completed" Can you provide a quick code sample of the view helper, controller or view code to make this work?

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  • Correct way to model recursive relationship in Django

    - by Yuval A
    My application has two node types: a parent node which can hold recursive child nodes. Think of it like the post-comment system in SO, but comments can be recursive: parent_1 child_11 child_12 child_121 child_3 parent_2 child_21 child_211 child_2111 Important to note that the parent nodes have different attributes and behavior than the child nodes. What is the correct (and presumably most efficient) way of modeling this relationship in Django?

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  • IntegrityError: foreign key violation upon delete

    - by Lukasz Korzybski
    I have Order and Shipment model. Shipment has a foreign key to Order. class Order(...): ... class Shipment() order = m.ForeignKey('Order') ... Now in one of my views I want do delete order object along with all related objects. So I invoke order.delete(). I have Django 1.0.4, PostgreSQL 8.4 and I use transaction middleware, so whole request is enclosed in single transaction. The problem is that upon order.delete() I get: ... File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 28, in _commit return self.connection.commit() IntegrityError: update or delete on table "main_order" violates foreign key constraint "main_shipment_order_id_fkey" on table "main_shipment" DETAIL: Key (id)=(45) is still referenced from table "main_shipment". I checked in connection.queries that proper queries are executed in proper order. First shipment is deleted, after that django executes delete on order row: {'time': '0.000', 'sql': 'DELETE FROM "main_shipment" WHERE "id" IN (17)'}, {'time': '0.000', 'sql': 'DELETE FROM "main_order" WHERE "id" IN (45)'} Foreign key have ON DELETE NO ACTION (default) and is initially deferred. I don't know why I get foreign key constraint violation. I also tried to register pre_delete signal and manually delete shipment objects before delete on order is called, but it resulted in the same error. I can change ON DELETE behaviour for this key in Postgres but it would be just a hack, I wonder if anyone has a better idea what's going on here. There is also a small detail, my Order model inherits from Cart model, so it actually doesn't have id field but cart_ptr_id and after DELETE on order is executed there is also DELETE on cart, but it seems unrelated? to the shipment-order problem so I simplified it in the example.

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  • How to render a Partial from a Model in Rails 2.3.5

    - by empire29
    I have a Rails 2.3.5 application and Im trying to render several Partials from within a Model (i know, i know -- im not supposed to). The reason im doing this is im integrating a Comet server (APE) into my Rails app and need to push updates out based on the Model's events (ex. after_create). I have tried doing this: ActionView::Base.new(Rails::Configuration.new.view_path).render(:partial => "pages/show", :locals => {:page => self}) Which allows me to render simple partials that don't user helpers, however if I try to user a link_to in my partial, i receive an error stating: undefined method `url_for' for nil:NilClass I've made sure that the object being passed into the "project_path(project)" is not nil. I've also tried including: include ActionView::Helpers::UrlHelper include ActionController::UrlWriter in the Module that contains the method that makes the above "render" call. Does anyone know how to work around this? Thanks

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  • Django: many-to-one fields and data integrity

    - by John
    Let's say that I have a Person who runs an inventory system. Each Person has some Cars, and each Car has a very large number of Parts (thousands, let's say). A Person, Bob, uses a Django form to create a Car. Now, Bob goes to create some Parts. It is only at the form level that Django knows that the Parts belong to some specific Car, and that the Parts.ForeignKey(Car) field should only have a specific Car as a choice. When creating a Part, you have to mess with the form's constructor or similar in order to limit the choice of Cars to only the cars owned by Bob. It does not seem proper that to enforce this ownership at the form level. It seems that other users' Cars must be inaccessible to anyone but the owner of the Car. What do you all think about this, and is there any way to enforce this?

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  • Django - calling full_clean() inside of clean() equivalent?

    - by orokusaki
    For transaction purposes, I need all field validations to run before clean() is done. Is this possible? My thinking is this: @transaction.commit_on_success def clean(self): # Some fun stuff here. self.full_clean() # I know this isn't correct, but it illustrates my point. but obviously that's not correct, because it would be recursive. Is there a way to make sure that everything that full_clean() does is done inside clean()?

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  • Doubt about django model API

    - by Clash
    Hello guys! So, here is what I want to do. I have a model Staff, that has a foreign key to the User model. I also have a model Match that has a foreign key to the User model. I want to select how much Matches every Staff has. I don't know how to do that, so far I only got it working for the User model. From Staff, it will not allow to annonate Match. This is what is working right now User.objects.annotate(ammount=Count("match")).filter(Q(ammount__gt=0)).order_by("ammount") And this is what I wanted to do Staff.objects.annotate(ammount=Count("match")).filter(Q(ammount__gt=0)).order_by("ammount") And by the way, is there any way to filter the matches? I want to filter the matches by a certain column. Thanks a lot in advance!

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  • XML file as model for django project

    - by Ankur Chauhan
    Hi, I have a XML file that is managed by other programs, I am writing a web service such that users are able to query this file. In essence i am using a xml based database instead of using sql as the model database in Django. how do i do this? all the tutorials that i find use a sql database in the backend. is there a way to use the xml file as a database.

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  • user model password field default password field in django

    - by imran-glt
    Hi, I've created a custom user model in my application. This user model is working fine, but there are a couple of problems I have with it. 1) The change password link in the my register.html page doesn't work? 2) The default password box on the add/edit page for a user is a little unfriendly. Ideally, what I'd like is the two password fields from the change password form on the add/edit user form in the admin, which will automatically turn convert the entered password into a valid encrypted password in Django. This would make the admin system MUCH friendlier and much more suited to my needs, as a fair number of user accounts will be created and maintained manually in this app, and the person responsible for doing so will likely be scared off at the sight of that admin field, or just type a clear text password and wonder why it doesn't work. Is this possible / How do I do this?

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  • Multiprogramming in Django, writing to the Database

    - by Marcus Whybrow
    Introduction I have the following code which checks to see if a similar model exists in the database, and if it does not it creates the new model: class BookProfile(): # ... def save(self, *args, **kwargs): uniqueConstraint = {'book_instance': self.book_instance, 'collection': self.collection} # Test for other objects with identical values profiles = BookProfile.objects.filter(Q(**uniqueConstraint) & ~Q(pk=self.pk)) # If none are found create the object, else fail. if len(profiles) == 0: super(BookProfile, self).save(*args, **kwargs) else: raise ValidationError('A Book Profile for that book instance in that collection already exists') I first build my constraints, then search for a model with those values which I am enforcing must be unique Q(**uniqueConstraint). In addition I ensure that if the save method is updating and not inserting, that we do not find this object when looking for other similar objects ~Q(pk=self.pk). I should mention that I ham implementing soft delete (with a modified objects manager which only shows non-deleted objects) which is why I must check for myself rather then relying on unique_together errors. Problem Right thats the introduction out of the way. My problem is that when multiple identical objects are saved in quick (or as near as simultaneous) succession, sometimes both get added even though the first being added should prevent the second. I have tested the code in the shell and it succeeds every time I run it. Thus my assumption is if say we have two objects being added Object A and Object B. Object A runs its check upon save() being called. Then the process saving Object B gets some time on the processor. Object B runs that same test, but Object A has not yet been added so Object B is added to the database. Then Object A regains control of the processor, and has allready run its test, even though identical Object B is in the database, it adds it regardless. My Thoughts The reason I fear multiprogramming could be involved is that each Object A and Object is being added through an API save view, so a request to the view is made for each save, thus not a single request with multiple sequential saves on objects. It might be the case that Apache is creating a process for each request, and thus causing the problems I think I am seeing. As you would expect, the problem only occurs sometimes, which is characteristic of multiprogramming or multiprocessing errors. If this is the case, is there a way to make the test and set parts of the save() method a critical section, so that a process switch cannot happen between the test and the set?

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  • Using set with values from a table

    - by gozzilli
    I'm writing a database of all DVDs I have at home. One of the fields, actors, I would like it to be a set of values from an other table, which is storing actors. So for every film I want to store a list of actors, all of which selected from a list of actors, taken from a different table. Is it possible? How do I do this? It would be a set of foreign keys basically. I'm using a MySQL database for a Django application (python), so any hint in SQL or Python would be much appreciated. I hope the question is clear, many thanks.

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