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• Django ForeignKey created empty?

  - by Scott Willman

  This seems very basic and I must be missing something, but here goes anyways... With two models like so: class School(models.Model): name = models.CharField("Official School Name", max_length=128) address = models.TextField("Address of the School", max_length=256) mascot = models.CharField("Name of the School Mascot", max_length=128) class StudentProfile(models.Model): name = models.CharField(max_length=128) school = models.ForeignKey(School) If the student gets created before the school, how do I give 'school' a default empty value? Is it blank or null or what? Thanks!

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• Django admin: how do I add an unrelated model field to a model change/add page?

  - by NP

  I have the following models: class Foo(models.Model): field1 = models.IntegerField() ... class Bar(models.Model): field1 = models.IntegerField() ... class Foo_bar(models.Model): foo = models.ForeignKey(Foo) bar = models.ForeignKey(Bar) ... In the admin, I want it so that in the Foo change/add page, you can specify a Bar object, and on save I want to create a Foo_bar object to represent the relationship. How can I do this through customizing the Admin site/ModelAdmins? Thanks.

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• How can I access the "through" object of a Django ManyToManyField?

  - by Macha

  I have the following models in my Django app. How can I from the Team model find all the User objects who have accepted as True in the Membership model? I know I need to use Team.objects.filter(), but I'm not sure how to check the value of the accepted field. from django.contrib.auth.models import User class Team(models.Model): members = models.ManyToManyField(User, through="Membership") class Membership(models.Model): user = models.ForeignKey(User) team = models.ForeignKey(Team) accepted = models.BooleanField(default=False)

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• What is Agile Modeling and why do I need it?

  What is Agile Modeling and why do I need it? Agile Modeling is an add-on to existing agile methodologies like Extreme programming (XP) and Rational Unified Process (RUP). Agile Modeling enables developers to develop a customized software development process that actually meets their current development needs and is flexible enough to adjust in the future. According to Scott Ambler, Agile Modeling consists of five core values that enable this methodology to be effective and light weight Agile Modeling Core Values: Communication Simplicity Feedback Courage Humility Communication is a key component to any successful project. Open communication between stakeholder and the development team is essential when developing new applications or maintaining legacy systems. Agile models promote communication amongst software development teams and stakeholders. Furthermore, Agile Models provide a common understanding of an application for members of a software development team allowing them to have a universal common point of reference. The use of simplicity in Agile Models enables the exploration of new ideas and concepts through the use of basic diagrams instead of investing the time in writing tens or hundreds of lines of code. Feedback in regards to application development is essential. Feedback allows a development team to confirm that the development path is on track. Agile Models allow for quick feedback from shareholders because minimal to no technical expertise is required to understand basic models. Courage is important because you need to make important decisions and be able to change direction by either discarding or refactoring your work when some of your decisions prove inadequate, according to Scott Ambler. As a member of a development team, we must admit that we do not know everything even though some of us think we do. This is where humility comes in to play. Everyone is a knowledge expert in their own specific domain. If you need help with your finances then you would consult an accountant. If you have a problem or are in need of help with a topic why would someone not consult with a subject expert? An effective approach is to assume that everyone involved with your project has equal value and therefore should be treated with respect. Agile Model Characteristics: Purposeful Understandable Sufficiently Accurate Sufficiently Consistent Sufficiently Detailed Provide Positive Value Simple as Possible Just Fulfill Basic Requirements According to Scott Ambler, Agile models are the most effective possible because the time that is invested in the model is just enough effort to complete the job. Furthermore, if a model isn’t good enough yet then additional effort can be invested to get more value out of the model. However if a model is good enough, for the current needs, or surpass the current needs, then any additional work done on the model would be a waste. It is important to remember that good enough is in the eye of the beholder, so this can be tough. In order for Agile Models to work effectively Active Stakeholder need to participation in the modeling process. Finally it is also very important to model with others, this allows for additionally input ensuring that all the shareholders needs are reflected in the models. How can Agile Models be incorporated in to our projects? Agile Models can be incorporated in to our project during the requirement gathering and design phases. As requirements are gathered the models should be updated to incorporate the new project details as they are defined and updated. Additionally, the Agile Models created during the requirement phase can be the bases for the models created during the design phase.  It is important to only add to the model when the changes fit within the agile model characteristics and they do not over complicate the design.

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• Thick models Vs. Business Logic, Where do you draw the distinction?

  - by TokenMacGuy

  Today I got into a heated debate with another developer at my organization about where and how to add methods to database mapped classes. We use sqlalchemy, and a major part of the existing code base in our database models is little more than a bag of mapped properties with a class name, a nearly mechanical translation from database tables to python objects. In the argument, my position was that that the primary value of using an ORM was that you can attach low level behaviors and algorithms to the mapped classes. Models are classes first, and secondarily persistent (they could be persistent using xml in a filesystem, you don't need to care). His view was that any behavior at all is "business logic", and necessarily belongs anywhere but in the persistent model, which are to be used for database persistence only. I certainly do think that there is a distinction between what is business logic, and should be separated, since it has some isolation from the lower level of how that gets implemented, and domain logic, which I believe is the abstraction provided by the model classes argued about in the previous paragraph, but I'm having a hard time putting my finger on what that is. I have a better sense of what might be the API (which, in our case, is HTTP "ReSTful"), in that users invoke the API with what they want to do, distinct from what they are allowed to do, and how it gets done. tl;dr: What kinds of things can or should go in a method in a mapped class when using an ORM, and what should be left out, to live in another layer of abstraction?

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• Models, collections...and then what? Processes?

  - by Dan

  I'm a LAMP-stack dev who's been more on the JavaScript side the last few years and really enjoying the Model + Collection approach to data entities that BackboneJS, etc. uses. It's helped me organize my code in such a way that it is extremely portable, keeping all my properties and methods in the scope (model, collection, etc.) in which they apply. One thing that keeps bugging me though is how to organize the next level up, the 'process layer' as you might call it, that can potentially operate on instances of either models or collections or whatever else. Where should methods like find() (which returns a collection) and create() (which returns a model) reside? I know some people would put a create() in the Collection prototype, but while a collection operates on models I don't think it's exactly right to create them. And while a find() would return a collection I don't think it correct to have that action within the collection prototype itself (it should be a layer up). Can anyone offer some examples of any patterns that employ some kind of OOP-friendly 'process' layer? I'm sorry if this is a fairly well-known discussion but I'm afraid I can't seem to find the terminology to search for.

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• Django m2m form appearing fields

  - by dana

  I have a classroom application,and a follow relation. Users can follow each other and can create classrooms.When a user creates a classroom, he can invite only the people that are following him. The Classroom model is a m2m to User table. i have in models. py: class Classroom(models.Model): creator = models.ForeignKey(User) classname = models.CharField(max_length=140, unique = True) date = models.DateTimeField(auto_now=True) open_class = models.BooleanField(default=True) members = models.ManyToManyField(User,related_name="list of invited members") and in models.py of the follow application: class Relations(models.Model): initiated_by = models.ForeignKey(User, editable=False) date_initiated = models.DateTimeField(auto_now=True, editable = False) follow = models.ForeignKey(User, editable = False, related_name = "follow") date_follow = models.DateTimeField(auto_now=True, editable = False) and in views.py of the classroom app: def save_classroom(request, username): if request.method == 'POST': u = User.objects.get(username=username) form = ClassroomForm(request.POST, request.FILES) if form.is_valid(): new_obj = form.save(commit=False) new_obj.creator = request.user r = Relations.objects.filter(initiated_by = request.user) # new_obj.members = new_obj.save() return HttpResponseRedirect('.') else: form = ClassroomForm() return render_to_response('classroom/classroom_form.html', { 'form': form, }, context_instance=RequestContext(request)) i'm using a ModelForm for the classroom form, and the default view, taking in consideration my many to many relation with User table, in the field Members, is a list of all Users in my database. But i only want in that list the users that are in a follow relationship with the logged in user - the one who creates the classroom. How can i do that? Thanks!

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• Django generic relation field reports that all() is getting unexpected keyword argument when no args

  - by Joshua

  I have a model which can be attached to to other models. class Attachable(models.Model): content_type = models.ForeignKey(ContentType) object_pk = models.TextField() content_object = generic.GenericForeignKey(ct_field="content_type", fk_field="object_pk") class Meta: abstract = True class Flag(Attachable): user = models.ForeignKey(User) flag = models.SlugField() timestamp = models.DateTimeField() I'm creating a generic relationship to this model in another model. flags = generic.GenericRelation(Flag) I try to get objects from this generic relation like so: self.flags.all() This results in the following exception: >>> obj.flags.all() Traceback (most recent call last): File "<console>", line 1, in <module> File "/usr/local/lib/python2.6/dist-packages/django/db/models/manager.py", line 105, in all return self.get_query_set() File "/usr/local/lib/python2.6/dist-packages/django/contrib/contenttypes/generic.py", line 252, in get_query_set return superclass.get_query_set(self).filter(**query) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 498, in filter return self._filter_or_exclude(False, *args, **kwargs) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 516, in _filter_or_exclude clone.query.add_q(Q(*args, **kwargs)) File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1675, in add_q can_reuse=used_aliases) File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1569, in add_filter negate=negate, process_extras=process_extras) File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1737, in setup_joins "Choices are: %s" % (name, ", ".join(names))) FieldError: Cannot resolve keyword 'object_id' into field. Choices are: content_type, flag, id, nestablecomment, object_pk, timestamp, user >>> obj.flags.all(object_pk=obj.pk) Traceback (most recent call last): File "<console>", line 1, in <module> TypeError: all() got an unexpected keyword argument 'object_pk' What have I done wrong?

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• Select those objects whose related objects IDs are *all* in given string

  - by Jannis

  Hi Django people, I want to build a frontend to a recipe database which enables the user to search for a list of recipes which are cookable with the ingredients the user supplies. I have the following models class Ingredient(models.Model): name = models.CharField(max_length=100, unique=True) slug = models.SlugField(max_length=100, unique=True) importancy = models.PositiveSmallIntegerField(default=4) […] class Amount(models.Model): recipe = models.ForeignKey('Recipe') ingredient = models.ForeignKey(Ingredient) […] class Rezept(models.Model): name = models.CharField(max_length=100) slug = models.SlugField() instructions = models.TextField() ingredients = models.ManyToManyField(Ingredient, through=Amount) […] and a rawquery which does exactly what I want: It gets all the recipes whose required ingredients are all contained in the list of strings that the user supplies. If he supplies more than necessary, it's fine too. query = "SELECT *, COUNT(amount.zutat_id) AS selected_count_ingredients, (SELECT COUNT(*) FROM amount WHERE amount.recipe_id = amount.id) AS count_ingredients FROM amount LEFT OUTER JOIN amount ON (recipe.id = recipe.recipe_id) WHERE amount.ingredient_id IN (%s) GROUP BY amount.id HAVING count_ingredient=selected_count_ingredient" % ",".join([str(ingredient.id) for ingredient in ingredients]) rezepte = Rezept.objects.raw(query) Now, what I'm looking for is a way that does not rely on .raw() as I would like to do it purely with Django's queryset methods. Additionally, it would be awesome if you guys knew a way of including the ingredient's importancy in the lookup so that a recipe is still shown as a result even though one of its ingredients (that has an importancy of 0) is not supplied by the user.

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• Global name not defined error in Django/Python trying to set foreignkey

  - by Mark

  Summary: I define a method createPage within a file called PageTree.py that takes a Source model object and a string. The method tries to generate a Page model object. It tries to set the Page model object's foreignkey to refer to the Source model object which was passed in. This throws a NameError exception! I'm trying to represent a website which is structured like a tree. I define the Django models Page and Source, Page representing a node on the tree and Source representing the contents of the page. (You can probably skip over these, this is a basic tree implementation using doubly linked nodes). class Page(models.Model): name = models.CharField(max_length=50) parent = models.ForeignKey("self", related_name="children", null=True); firstChild = models.ForeignKey("self", related_name="origin", null=True); nextSibling = models.ForeignKey("self", related_name="prevSibling", null=True); previousSibling = models.ForeignKey("self", related_name="nxtSibling", null=True); source = models.ForeignKey("Source"); class Source(models.Model): #A source that is non dynamic will be refered to as a static source #Dynamic sources contain locations that are names of functions #Static sources contain locations that are places on disk name = models.CharField(primary_key=True, max_length=50) isDynamic = models.BooleanField() location = models.CharField(max_length=100); I've coded a python program called PageTree.py which allows me to request nodes from the database and manipulate the structure of the tree. Here is the trouble making method: def createPage(pageSource, pageName): page = Page() page.source = pageSource page.name = pageName page.save() return page I'm running this program in a shell through manage.py in Windows 7 manage.py shell from mysite.PageManager.models import Page, Source from mysite.PageManager.PageTree import * ... create someSource = Source(), populate the fields, and save it ... createPage(someSource, "test") ... NameError: global name 'source' is not defined When I type in the function definition for createPage into the shell by hand, the call works without error. This is driving me bonkers and help is appreciated.

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• Implementing a popularity algorithm in Django

  - by TheLizardKing

  I am creating a site similar to reddit and hacker news that has a database of links and votes. I am implementing hacker news' popularity algorithm and things are going pretty swimmingly until it comes to actually gathering up these links and displaying them. The algorithm is simple: Y Combinator's Hacker News: Popularity = (p - 1) / (t + 2)^1.5` Votes divided by age factor. Where` p : votes (points) from users. t : time since submission in hours. p is subtracted by 1 to negate submitter's vote. Age factor is (time since submission in hours plus two) to the power of 1.5.factor is (time since submission in hours plus two) to the power of 1.5. I asked a very similar question over yonder http://stackoverflow.com/questions/1964395/complex-ordering-in-django but instead of contemplating my options I choose one and tried to make it work because that's how I did it with PHP/MySQL but I now know Django does things a lot differently. My models look something (exactly) like this class Link(models.Model): category = models.ForeignKey(Category) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add = True) modified = models.DateTimeField(auto_now = True) fame = models.PositiveIntegerField(default = 1) title = models.CharField(max_length = 256) url = models.URLField(max_length = 2048) def __unicode__(self): return self.title class Vote(models.Model): link = models.ForeignKey(Link) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add = True) modified = models.DateTimeField(auto_now = True) karma_delta = models.SmallIntegerField() def __unicode__(self): return str(self.karma_delta) and my view: def index(request): popular_links = Link.objects.select_related().annotate(karma_total = Sum('vote__karma_delta')) return render_to_response('links/index.html', {'links': popular_links}) Now from my previous question, I am trying to implement the algorithm using the sorting function. An answer from that question seems to think I should put the algorithm in the select and sort then. I am going to paginate these results so I don't think I can do the sorting in python without grabbing everything. Any suggestions on how I could efficiently do this? EDIT This isn't working yet but I think it's a step in the right direction: from django.shortcuts import render_to_response from linkett.apps.links.models import * def index(request): popular_links = Link.objects.select_related() popular_links = popular_links.extra( select = { 'karma_total': 'SUM(vote.karma_delta)', 'popularity': '(karma_total - 1) / POW(2, 1.5)', }, order_by = ['-popularity'] ) return render_to_response('links/index.html', {'links': popular_links}) This errors out into: Caught an exception while rendering: column "karma_total" does not exist LINE 1: SELECT ((karma_total - 1) / POW(2, 1.5)) AS "popularity", (S... EDIT 2 Better error? TemplateSyntaxError: Caught an exception while rendering: missing FROM-clause entry for table "vote" LINE 1: SELECT ((vote.karma_total - 1) / POW(2, 1.5)) AS "popularity... My index.html is simply: {% block content %} {% for link in links %} karma-up {{ link.karma_total }} karma-down {{ link.title }} Posted by {{ link.user }} to {{ link.category }} at {{ link.created }} {% empty %} No Links {% endfor %} {% endblock content %} EDIT 3 So very close! Again, all these answers are great but I am concentrating on a particular one because I feel it works best for my situation. from django.db.models import Sum from django.shortcuts import render_to_response from linkett.apps.links.models import * def index(request): popular_links = Link.objects.select_related().extra( select = { 'popularity': '(SUM(links_vote.karma_delta) - 1) / POW(2, 1.5)', }, tables = ['links_link', 'links_vote'], order_by = ['-popularity'], ) return render_to_response('links/test.html', {'links': popular_links}) Running this I am presented with an error hating on my lack of group by values. Specifically: TemplateSyntaxError at / Caught an exception while rendering: column "links_link.id" must appear in the GROUP BY clause or be used in an aggregate function LINE 1: ...karma_delta) - 1) / POW(2, 1.5)) AS "popularity", "links_lin... Not sure why my links_link.id wouldn't be in my group by but I am not sure how to alter my group by, django usually does that.

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• Should database-models (conceptual or physical) be reviewed by DBAs?

  - by user61852

  Where I work, new applications that are being developed that will use their own relational database, must have their database-models (conceptual, then physical ) reviewed and aproved by DBAs. Things looked after are normalization, antipatterns, table and column naming standards, etc. Is this really a DBA's responsability to do this ? or should it be, in a greater extend, the responsability of app designers and architects ?

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• What good books are out there on program execution models? [on hold]

  - by murungu

  Can anyone out there name a few books that address the topic of program execution models?? I want a book that can answer questions such as... What is the difference between interpreted and compiled languages and what are the performance consequences at runtime?? What is the difference between lazy evaluation, eager evaluation and short circuit evaluation?? Why would one choose to use one evaluation strategy over another?? How do you simulate lazy evaluation in a language that favours eager evaluation??

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• Django: What's an awesome plugin to maintain images in the admin?

  - by meder

  I have an articles entry model and I have an excerpt and description field. If a user wants to post an image then I have a separate ImageField which has the default standard file browser. I've tried using django-filebrowser but I don't like the fact that it requires django-grappelli nor do I necessarily want a flash upload utility - can anyone recommend a tool where I can manage image uploads, and basically replace the file browse provided by django with an imagepicking browser? In the future I'd probably want it to handle image resizing and specify default image sizes for certain article types. Edit: I'm trying out adminfiles now but I'm having issues installing it. I grabbed it and added it to my python path, added it to INSTALLED_APPS, created the databases for it, uploaded an image. I followed the instructions to modify my Model to specify adminfiles_fields and registered but it's not applying in my admin, here's my admin.py for articles: from django.contrib import admin from django import forms from articles.models import Category, Entry from tinymce.widgets import TinyMCE from adminfiles.admin import FilePickerAdmin class EntryForm( forms.ModelForm ): class Media: js = ['/media/tinymce/tiny_mce.js', '/media/tinymce/load.js']#, '/media/admin/filebrowser/js/TinyMCEAdmin.js'] class Meta: model = Entry class CategoryAdmin(admin.ModelAdmin): prepopulated_fields = { 'slug': ['title'] } class EntryAdmin( FilePickerAdmin ): adminfiles_fields = ('excerpt',) prepopulated_fields = { 'slug': ['title'] } form = EntryForm admin.site.register( Category, CategoryAdmin ) admin.site.register( Entry, EntryAdmin ) Here's my Entry model: class Entry( models.Model ): LIVE_STATUS = 1 DRAFT_STATUS = 2 HIDDEN_STATUS = 3 STATUS_CHOICES = ( ( LIVE_STATUS, 'Live' ), ( DRAFT_STATUS, 'Draft' ), ( HIDDEN_STATUS, 'Hidden' ), ) status = models.IntegerField( choices=STATUS_CHOICES, default=LIVE_STATUS ) tags = TagField() categories = models.ManyToManyField( Category ) title = models.CharField( max_length=250 ) excerpt = models.TextField( blank=True ) excerpt_html = models.TextField(editable=False, blank=True) body_html = models.TextField( editable=False, blank=True ) article_image = models.ImageField(blank=True, upload_to='upload') body = models.TextField() enable_comments = models.BooleanField(default=True) pub_date = models.DateTimeField(default=datetime.datetime.now) slug = models.SlugField(unique_for_date='pub_date') author = models.ForeignKey(User) featured = models.BooleanField(default=False) def save( self, force_insert=False, force_update= False): self.body_html = markdown(self.body) if self.excerpt: self.excerpt_html = markdown( self.excerpt ) super( Entry, self ).save( force_insert, force_update ) class Meta: ordering = ['-pub_date'] verbose_name_plural = "Entries" def __unicode__(self): return self.title Edit #2: To clarify I did move the media files to my media path and they are indeed rendering the image area, I can upload fine, the <<<image>>> tag is inserted into my editable MarkItUp w/ Markdown area but it isn't rendering in the MarkItUp preview - perhaps I just need to apply the |upload_tags into that preview. I'll try adding it to my template which posts the article as well.

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• Django Forms, Foreign Key and Initial retuen all associated values

  - by gramware

  I a working with Django forms. The issue I have is that Foreign Key fields and those using initial take all associated entries (all records associated with that record other then the one entry i wanted e.g instead of getting a primary key, i get the primary key, post subject, post body and all other values attributed with that record). The form and the other associated queries still work well, but this behaviour is clogging my database. How do i get the specific field i want instead of all records. An example of my models is here: A form field for childParentId returns postID, postSubject and postBody instead of postID alone. Also form = ForumCommentForm(initial = {'postSubject':forum.objects.get(postID = postID), }) returns all records related to postID. class forum(models.Model): postID = models.AutoField(primary_key=True) postSubject = models.CharField(max_length=25) postBody = models.TextField() postPoster = models.ForeignKey(UserProfile) postDate = models.DateTimeField(auto_now_add=True) child = models.BooleanField() childParentId = models.ForeignKey('self',blank=True, null=True) deleted = models.BooleanField() def __unicode__(self): return u'%s %s %s %s %s' % (self.postSubject, self.postBody, self.postPoster, self.postDate, self.postID

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• Filter Queryset in Django inlineformset_factory

  - by Dave

  I am trying to use inlineformset_factory to generate a formset. My models are defined as: class Measurement(models.Model): subject = models.ForeignKey(Animal) experiment = models.ForeignKey(Experiment) assay = models.ForeignKey(Assay) values = models.CommaSeparatedIntegerField(blank=True, null=True) class Experiment(models.Model): date = models.DateField() notes = models.TextField(max_length = 500, blank=True) subjects= models.ManyToManyField(Subject) in my view i have: def add_measurement(request, experiment_id): experiment = get_object_or_404(Experiment, pk=experiment_id) MeasurementFormSet = inlineformset_factory(Experiment, Measurement, extra=10, exclude=('experiment')) if request.method == 'POST': formset = MeasurementFormSet(request.POST,instance=experiment) if formset.is_valid(): formset.save() return HttpResponseRedirect( experiment.get_absolute_url() ) else: formset = MeasurementFormSet(instance=experiment) return render_to_response("data_entry_form.html", {"formset": formset, "experiment": experiment }, context_instance=RequestContext(request)) but i want to restrict the Measurement.subject field to only subjects defined in the Experiment.subjects queryset. I have tried a couple of different ways of doing this but I am a little unsure what the best way to accomplish this is. I tried to over-ride the BaseInlineFormset class with a new queryset, but couldnt figure out how to correctly pass the experiment parameter.

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• Django Forms, Foreign Key and Initial return all associated values

  - by gramware

  I a working with Django forms. The issue I have is that Foreign Key fields and those using initial take all associated entries (all records associated with that record other then the one entry i wanted e.g instead of getting a primary key, i get the primary key, post subject, post body and all other values attributed with that record). The form and the other associated queries still work well, but this behaviour is clogging my database. How do i get the specific field i want instead of all records. An example of my models is here: A form field for childParentId returns postID, postSubject and postBody instead of postID alone. Also form = ForumCommentForm(initial = {'postSubject':forum.objects.get(postID = postID), }) returns all records related to postID. class forum(models.Model): postID = models.AutoField(primary_key=True) postSubject = models.CharField(max_length=25) postBody = models.TextField() postPoster = models.ForeignKey(UserProfile) postDate = models.DateTimeField(auto_now_add=True) child = models.BooleanField() childParentId = models.ForeignKey('self',blank=True, null=True) deleted = models.BooleanField() def __unicode__(self): return u'%s %s %s %s %s' % (self.postSubject, self.postBody, self.postPoster, self.postDate, self.postID

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• django ManyToMany through help

  - by dotty

  Hay I've got a question about relationships. I want to Users to have Friendships. So a User can be a friend with another User. I'm assuming i'll need to use the ManyToManyField, through a Friendship table. But i cannot get it to work. Any ideas? Here are my models. class User(models.Model): username = models.CharField(max_length=999) password = models.CharField(max_length=999) created_on = models.DateField(auto_now = False, auto_now_add = True) updated_on = models.DateField(auto_now = True, auto_now_add = False) friends = models.ManyToManyField('User', through='Friendship') class Friendship(models.Model): user = models.ForeignKey('User') friend = models.ForeignKey('User') Thanks

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• ValueError with multi-table inheritance in Django Admin

  - by jorde

  I created two new classes which inherit model Entry: class Entry(models.Model): LANGUAGE_CHOICES = settings.LANGUAGES language = models.CharField(max_length=2, verbose_name=_('Comment language'), choices=LANGUAGE_CHOICES) user = models.ForeignKey(User) country = models.ForeignKey(Country, null=True, blank=True) created = models.DateTimeField(auto_now=True) class Comment(Entry): comment = models.CharField(max_length=2000, blank=True, verbose_name=_('Comment in English')) class Discount(Entry): discount = models.CharField(max_length=2000, blank=True, verbose_name=_('Comment in English')) coupon = models.CharField(max_length=2000, blank=True, verbose_name=_('Coupon code if needed')) After adding these new models to admin via admin.site.register I'm getting ValueError when trying to create a comment or a discount via admin. Adding entries works fine. Error msg: ValueError at /admin/reviews/discount/add/ Cannot assign "''": "Discount.discount" must be a "Discount" instance. Request Method: GET Request URL: http://127.0.0.1:8000/admin/reviews/discount/add/ Exception Type: ValueError Exception Value: Cannot assign "''": "Discount.discount" must be a "Discount" instance. Exception Location: /Library/Python/2.6/site-packages/django/db/models/fields/related.py in set, line 211 Python Executable: /usr/bin/python Python Version: 2.6.1

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• How to limit choice field options based on another choice field in django admin

  - by umnik700

  I have the following models: class Category(models.Model): name = models.CharField(max_length=40) class Item(models.Model): name = models.CharField(max_length=40) category = models.ForeignKey(Category) class Demo(models.Model): name = models.CharField(max_length=40) category = models.ForeignKey(Category) item = models.ForeignKey(Item) In the admin interface when creating a new Demo, after user picks category from the dropdown, I would like to limit the number of choices in the "items" drop-down. If user selects another category then the item choices should update accordingly. I would like to limit item choices right on the client, before it even hits the form validation on the server. This is for usability, because the list of items could be 1000+ being able to narrow it down by category would help to make it more manageable. Is there a "django-way" of doing it or is custom JavaScript the only option here?

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• django left join with null

  - by SledgehammerPL

  The model: class Product(models.Model): name = models.CharField(max_length = 128) def __unicode__(self): return self.name class Receipt(models.Model): name = models.CharField(max_length=128) components = models.ManyToManyField(Product, through='ReceiptComponent') class Admin: pass def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive The idea: there are a components on stock. I'd like to find out which recipes I can made with components which I have. It's not easy - but possible - I made a SQL view, which gets the solution. But I'm learning python and Django so I'd like to make it Django-style ;D The concept of solution: get the set of recipes which has at last one component: list_of_available_components = ReceiptComponent.objects.filter(product__in=list_of_available_products).distinct() list_of_related_receipts = Receipt.objects.filter(receiptcomponent__in = list_of_available_components).distinct() get recipes (from list_of_related_receipts) which has not at last one component list_of_incomplete_recipes = (SELECT * FROM drinkbook_receiptcomponent LEFT JOIN drinkstore_stock_products USING(product_id) WHERE drinkstore_stock_products.stock_id IS NULL AND receipt_id IN (SELECT receipt_id FROM drinkbook_receiptcomponent JOIN drinkstore_stock_products USING(product_id))) get recipes (from list_of_related_receipts) which are not in "list_of_incomplete_recipes"

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• No drop packets using the error models for wirelesss scenario ?

  I am trying to use the error model in ns2 with wireless links, I am using ns2.33. I tried the uniform error model and the markov chain model. No errors from ns but when I am trying to find the dropped packets due to corruption I can not find any of them using either the uniform or markov models. So please help me if I made any error in using the error model. to search for dropped packets I am using eid@eid-laptop:~/code/ns2/noisy$ cat mixed.tr | grep d My code is available here : http://pastebin.com/f68749435

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• Easiest way to rename a model using Django/South?

  - by vaughnkoch

  Hi everyone, I've been hunting for an answer to this on South's site, google, and SO, but couldn't find a simple way to do this. I want to rename a Django model using South. Say you have the following: class Foo(models.Model): name = models.CharField() class FooTwo(models.Model): name = models.CharField() foo = models.ForeignKey(Foo) and you want to convert Foo to Bar, namely class Bar(models.Model): name = models.CharField() class FooTwo(models.Model): name = models.CharField() foo = models.ForeignKey(Bar) To keep it simple, I'm just trying to change the name from Foo to Bar, but ignore the 'foo' member in FooTwo for now. What's the easiest way to do this using South? a) I could probably do a data migration, but that seems pretty involved. b) Write a custom migration, e.g. db.rename_table('city_citystate', 'geo_citystate'), but I'm not sure how to fix the foreign key in this case. c) An easier way that you know? Thanks!

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• django access to parent

  - by SledgehammerPL

  model: class Product(models.Model): name = models.CharField(max_length = 128) (...) def __unicode__(self): return self.name class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Product, through='ReceiptComponent') def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive And now I'd like to get list of the most often useable products: ReceiptComponent.objects.values('product').annotate(Count('product')).order_by('-product__count' the example result: [{'product': 3, 'product__count': 5}, {'product': 6, 'product__count': 4}, {'product': 5, 'product__count': 3}, {'product': 7, 'product__count': 2}, {'product': 1, 'product__count': 2}, {'product': 11, 'product__count': 1}, {'product': 8, 'product__count': 1}, {'product': 4, 'product__count': 1}, {'product': 9, 'product__count': 1}] It's almost what I need. But I'd prefer having Product object not product value, because I'd like to use this in views.py for generating list.

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• Django populate select field based on model query

  - by Mike

  I have the following model class DNS(models.Model): domain = models.ForeignKey(Domain) host_start = models.CharField(max_length=150, blank=True, null=True) type = models.SmallIntegerField(max_length=1, default=0, choices=DNS_CHOICE) value = models.SmallIntegerField(max_length=3, default=0, blank=True, null=True) ip = models.IPAddressField(blank=True, null=True) host_end = models.ForeignKey("DNS", blank=True, null=True) other_end = HostnameField(max_length=150, blank=True, null=True) created = models.DateTimeField(auto_now_add=True) sticky = models.BooleanField(default=0) other = models.BooleanField(default=0) When I try to init a form with just foreignkeys on host_end.. it always shows all entries in the DNS table domain = Domain.objects.get(id=request.GET['domain'], user=request.user, active=1) form = DNSFormCNAME(initial={'ip': settings.MAIN_IP, 'type': request.GET['type'], 'host_end': DNS.objects.filter(domain=domain)}) I just want the zones that match that domain.. not all domains.

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