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Tag "models"

93 snippets

Snippet List

Binding signals to abstract models

Intro ----- I found a question on SO for which Justin Lilly's answer was correct but not as thorough as I'd like, so I ended up working on a simple snippet that shows how to bind signals at runtime, which is nifty when you want to bind signals to an abstract class. Bonus: simple cache invalidation! Question -------- [How do I use Django signals with an abstract model?](http://stackoverflow.com/questions/2692551/how-do-i-use-django-signals-with-an-abstract-model) I have an abstract model that keeps an on-disk cache. When I delete the model, I need it to delete the cache. I want this to happen for every derived model as well. If I connect the signal specifying the abstract model, this does not propagate to the derived models: pre_delete.connect(clear_cache, sender=MyAbstractModel, weak=False) If I try to connect the signal in an init, where I can get the derived class name, it works, but I'm afraid it will attempt to clear the cache as many times as I've initialized a derived model, not just once. Where should I connect the signal? Answer ------ I've created a custom manager that binds a post_save signal to every child of a class, be it abstract or not. This is a one-off, poorly tested code, so beware! It works so far, though. In this example, we allow an abstract model to define CachedModelManager as a manager, which then extends basic caching functionality to the model and its children. It allows you to define a list of volatile keys that should be deleted upon every save (hence the post_save signal) and adds a couple of helper functions to generate cache keys, as well as retrieving, setting and deleting keys. This of course assumes you have a cache backend setup and working properly.

  • managers
  • models
  • cache
  • model
  • manager
  • signals
  • abstract
  • signal
  • contribute_to_class
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Per-Instance On-Model M2M Caching

If you are like me and you find yourself often using M2M fields for tons of other on-model methods, in templates, and views alike, try using this quick and dirty caching. I show the use of a "through" model for the m2m, but that is purely optional. For example, let's say we need to do several different things with our list of beads, the old way is... # views.py necklace = Necklace.objects.get(id=1) bead = Bead.objects.get(id=1) if bead in necklace.beads.all(): # this bead is here! # template necklace.html {% for bead in necklace.beads.all %} <li>{{ bead }}</li> {% endfor %} ...which would hit the database twice. Instead, we do this: # views.py necklace = Necklace.objects.get(id=1) bead = Bead.objects.get(id=1) if bead in necklace.get_beads(): # this bead is here! # template necklace.html {% for bead in necklace.get_beads %} <li>{{ bead }}</li> {% endfor %} Which only does one hit on the database. While we could have easily set the m2m query to a variable and passed it to the template to do the same thing, the great thing is how you can build extra methods on the model that use the m2m field but share the cache with anyone down the line using the same m2m field. I'm by no means an expert, so if there is something here I've done foolishly, let me know.

  • models
  • cache
  • m2m
  • caching
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Compare two instances of the same model

This compares two objects (of the same model) and returns a tuple containing dictionaries with the changed attributes. Note that ALL attributes are run through comparison, so if you are modifying non-field attributes at runtime, these will also be included. Excluded keys is a tuple containing the names if attributes you do not want to include in the comparison loop (i.e. attributes which changes are irrelevant).

  • models
  • comparison
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PositionField

**This is a model field for managing user-specified positions.** Usage ===== Add a `PositionField` to your model; that's just about it. If you want to work with all instances of the model as a single collection, there's nothing else required. In order to create collections based on another field in the model (a `ForeignKey`, for example), set `unique_for_field` to the name of the field. It's probably also a good idea to wrap the `save` method of your model in a transaction since it will trigger another query to reorder the other members of the collection. Here's a simple example: from django.db import models, transaction from positions.fields import PositionField class List(models.Model): name = models.CharField(max_length=50) class Item(models.Model): list = models.ForeignKey(List, db_index=True) name = models.CharField(max_length=50) position = PositionField(unique_for_field='list') # not required, but probably a good idea save = transaction.commit_on_success(models.Model.save) Indices ------- In general, the value assigned to a `PositionField` will be handled like a list index, to include negative values. Setting the position to `-2` will cause the item to be moved to the second position from the end of the collection -- unless, of course, the collection has fewer than two elements. Behavior varies from standard list indices when values greater than or less than the maximum or minimum positions are used. In those cases, the value is handled as being the same as the maximum or minimum position, respectively. `None` is also a special case that will cause an item to be moved to the last position in its collection. Limitations =========== * Unique constraints can't be applied to `PositionField` because they break the ability to update other items in a collection all at once. This one was a bit painful, because setting the constraint is probably the right thing to do from a database consistency perspective, but the overhead in additional queries was too much to bear. * After a position has been updated, other members of the collection are updated using a single SQL `UPDATE` statement, this means the `save` method of the other instances won't be called. More === More information, including an example app and tests, is available on [Google Code](http://code.google.com/p/django-positions/).

  • lists
  • models
  • fields
  • model
  • field
  • list
  • sorting
  • ordering
  • collection
  • collections
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Translated choices fields

- Choices are saved as the key integers. - Admin will show the correct translation in forms. - You can reuse the make_choices function for other choices fields. - Bad side: bin/make_messages.py won't get the choices values automatically, you have to add them in the .po's by hand.

  • models
  • choices
  • i18n
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Decouple 'help_text' attribute from field definition

I found model definitions with large number of fields with long help_text unreadable and feel that help_text doesn't really belong to field definition. With this snippet help_text attributes can live outside field definitions in inner HelpText class so field definitions become shorter and more readable. Usage: from django.db import models import readable_models class MyModel(models.Model): __metaclass__ = readable_models.ModelBase name = models.CharField('Name', max_length=30) address = models.CharField('Address', max_length=255) # ... long list of fields class HelpText: name = 'The name ...' address = 'Example: <very verbose example is here>'

  • models
  • help_text
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jQuery color picker model field

This uses the Really Simple Color Picker in jQuery: http://www.web2media.net/laktek/2008/10/27/really-simple-color-picker-in-jquery/ Get source from there or GitHub: http://github.com/laktek/really-simple-color-picker/tree/master

  • models
  • admin
  • jquery
  • widgets
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Custom color field with Javascript color picker

A custom model field 'ColorField' which stores a hex color value like '#FFFFFF' and shows a Javascript color picker in the admin rather than a raw text field. It is written to work with the current trunk (i.e. after newforms-admin merge). You'll need the ColorPicker2.js file found at [www.mattkruse.com](http://www.mattkruse.com/javascript/colorpicker/combined_compact_source.html) (his license prohibits including the file here). This should be placed in the 'js' folder of your admin media. The snippet includes a python source file which can be placed wherever you wish, and a template which by default should be placed in a folder 'widget' somewhere on your template path. You can put it elsewhere, just update the path ColorWidget.render The custom field at present does not validate that the text is a valid hex color value, that'd be a nice addition.

  • newforms
  • javascript
  • models
  • admin
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Another Multiform

MultiForm and MultiModelForm Based on a PrefixDict class I wrote and thus very lean. Lacks a little documentation, though class MyMultiForm(ModelMultiForm): class Meta: localized_fields = '__all__' form_classes = OrderedDict(( ('form1', Form1), ('form2', Form2), )) Subfields are named `form-name` `prefix_sep` `subfield-name`. `prefix_sep` defaults to `-`. For access in templates, use `form.varfields`, which uses `var_prefix_sep` (default: `_`), instead. multiform.varfields()['form1_field1']

  • models
  • forms
  • multiform
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Models for Postal Addresses

Here's some fairly normalized models for representing postal addresses. Making postal_code a separate model would probably be the only way to get it to a level that everyone would agree is 2NF, but we handle a lot of international addresses so that isn't really feasible. Country and StateProvince are intended to be populated with data from ISO 3166. I'd include the SQL I used with that data, but it's very long and there's no attach feature. Also, I'd probably be violating ISO's copyright.

  • models
  • countries
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Extended i18n base model

This snippet is an extension of [i18n base model for translatable content](http://djangosnippets.org/snippets/855/) so all the same usage applies. I have extended this module in several ways to make it more fully featured. * `I18NMixin` can be an additional (via multiple inheritance) or alternative superclass for your models juxtaposed with an `I18NModel`. * Adds a property `_` to access the appropriate I18NModel. `trans` aliases this (or rather vice versa) for template access. * In a call to `.filter` you can query on translated fields by wrapping those fields in a call to i18nQ. I like to import this as _ if I haven't already used that import. * A call to I18NFieldset will return an inline for use in the builtin admin app. I like to call this inline to the assignment to inlines. * If you need abstracted access to the I18N model from a model, I've added a property I18N referring to it. I've been using this with great convenience and stability.

  • models
  • i18n
  • metaclass
  • translated-content
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Get derived model instance

Get derived model without storing their names or content types in databases. You write only one line, it expands into only one SQL-query (with many LEFT OUTER JOIN's). Model definition example: class BaseModel(models.Model): foo = models.IntegerField(null=True) derived = DerivedManager() class FirstChild(BaseModel): bar = models.IntegerField(null=True) class SecondChild(BaseModel): baz = models.IntegerField(null=True) How to use: >>> f = FirstChild.objects.create() >>> s = SecondChild.objects.create() >>> print list(BaseModel.objects.all() [<BaseModel object 1>, <BaseModel object 2>] >>> print list(BaseModel.derived.all() [<FirstChild object 1>, <SecondChild object 2>] >>> print BaseModel.derived.get(pk=s.pk) <SecondChild object 2>

  • models
  • orm
  • inheritance
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Compare objects list and get a list of object to inserted or updated

**Problem** You have an input `json` with which you will create a list of objects, you have to validate that the object will be created if it not exists, if exists determine whether to upgrade or discard depending of they have not undergone any changes. Solution 1) With the input `json` will be created the list of objects of the class that we insert or updatee 2) Read all fields in the database, using one of the fields as key to creating a dictionary with the objects in the database 3) Compare the objects and determine if it will be updated, inserted or discarded Django problem: by default only compares the level objects using the primary key (id). Compare field by field is the solution to determine if the object has changed. hints: The _state field is present in every object, and it will produce a random memory location, You can find cache fields so you need to remove these begins with underscore `_`. The fields excluded can be fk, and these fields produce field_id, so you will needs to exclude it class Country(models.Model): # country code 'MX' -> Mexico code = models.CharField(max_length=2) name = models.CharField(max_length=15) class Client(models.Model): # id=1, name=pedro, country.code=MX, rfc=12345 name = models.CharField(max_length=100) country = models.ForeignKey(Country) rfc = models.CharField(max_length=13) Country.objects.create(**{'code': 'MX', 'name': 'Mexico'}) # creating the country Client(**{'id':1, 'name':'pedro', 'country': country, 'rfc':12345}) # creating the client obj_db = Client.objects.get(id=1) country = Country.objects.get(code='MX') obj_no_db = Client(**{'id':1, 'name':'pedro', 'country': country, 'rfc':12345}) obj_db == obj_no_db # True obj_no_db = Client(**{'id':1, 'name':'pedro', 'country': country, 'rfc':1}) obj_db == obj_no_db # True # but isn't True because the rfc has change, how can compare field by field obj_db.rfc == obj_no_db.rfc # False, I was expected this result when compare obj_db == obj_no_db because they are not equal **Solution to compare field by field** _obj_1 = [(k,v) for k,v in obj_db.__dict__.items() if k != '_state'] _obj_2 = [(k,v) for k,v in obj_no_db.__dict__.items() if k != '_state'] _obj_1 == _obj_2 # False This is only for one object, and you can include in `__eq__` method in your model, but what happen if you need compare a list of object to bulk for insert or update with `django-bulk-update`. Well my snipped pretends solve that. so **How can use it.** obj_list = [<Object Client>, <Object Client>, <Object Client>, <Object Client>] get_insert_update(Client, 'id', obj_list) exclude_fields = ['country'] get_insert_update(Client, 'id', obj_list, exclude_fields=exclude_fields)

  • models
  • bulk
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