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Tag "model"

137 snippets

Snippet List

Custom Django manager that excludes subclasses

When you're using Django model inheritance, sometimes you want to be able to get objects of the base class that aren't instances of any of the subclasses. You might expect the obvious way of doing this, `SuperModel.objects.filter(submodel__isnull=True)`, to work, but unfortunately it doesn't. (Neither does `SuperModel.objects.filter(submodel__supermodel_ptr=None)`, or any other convoluted way I could think of doing it.) Here's a nicer approach for doing this. [The blog entry is here.](http://sciyoshi.com/blog/2008/aug/07/custom-django-manager-excludes-subclasses/)

  • managers
  • models
  • model
  • subclass
  • manager
  • inheritance
  • subclasses
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Using Python properties in models

After reading the comment to my [snippet #49](http://www.djangosnippets.org/snippets/49/) it occurs to me that Python properties may not be obvious to everyone, and may be underutilized in Django models. Here is a simple example demonstrating a property to format a Person's name.

  • property
  • model
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JsonObjectField

This fields.py file defines a new model field type, "JsonObjectField," which is designed to allow the storage of arbitrary Python objects in Django TextFields. It is intended primarily to allow the storage of Python dictionaries or list objects. As the name implies, it converts objects to JSON for storage; this conversion happens transparently, so from your model's perspective, the field stores and retrieves the actual objects.

  • model
  • json
  • database
  • object
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Model Hooks

Runs model methods on save, create, update, delete Similar to Rails hooks **Usage:** *in models.py* from myproject.hooks import connect_hooks class MyModel(models.Model): #... # only on first save of a newly created object def before_create(self): print self def after_create(self): print self # not on first save of a newly created object def before_update(self): print self def after_update(self): print self # any save, new object or update def before_save(self): print self def after_save(self): print self # delete, self is still available after delete def before_delete(self): print self def after_delete(self): print self **connect_hooks(MyModel)**

  • model
  • hooks
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another UserForeignKey

This is another foreign key to User model. User is automatically associated before save. Requires: [ThreadlocalsMiddleware](http://code.djangoproject.com/wiki/CookBookThreadlocalsAndUser) Inspired by: [snippet 509](http://www.djangosnippets.org/snippets/509/)

  • foreignkey
  • model
  • user
  • field
  • users
  • user-foreign-key
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Generic Permissions

A mixin to define permissions on models. This is more of an abstract model to subclass/customise than a plug-in solution. Explanations are [here](http://www.muhuk.com/2009/05/django-permission-system/).

  • models
  • model
  • permission
  • authorization
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ManyToManyField no syncdb

**Sumary** M2M relation without creating table. Normally you should specify m2m only in *one* model, thus widgets for many-to-many relations will be displayed inline on whichever model contains the actual reference to the ManyToManyField. But if you want to be able to have widgets displayed on both form you need some tricks, for example using intermediary-models can help, but you will not get multiselect widget (and in case of inlining extra = multi). Also you can write your own form which takes care about adding widget (just 1 line) and setting default values and saving it (more than few lines of code). If you try ManyToManyField with same db_table specified, the only problem will be in syncdb (it will try to create two identical tables) and the only thing our class does is preventing creation of table for M2M, so in one model you should use ManyToManyField and in another ManyToManyField_NoSyncdb with the same db_table argument. **Example** So to have M2M widgets in both forms you can write: class User(models.Model): #... groups = ManyToManyField('Group', related_name='groups', db_table=u'USERS_TO_GROUPS') class Group(models.Model): #... users = ManyToManyField_NoSyncdb(User, related_name='users', db_table=u'USERS_TO_GROUPS')

  • model
  • field
  • manytomany
  • manytomanyfield
  • syncdb
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Address model

This is standart address model. Must match US / GB / French address and other... Specifics locales fields are notice by comments.

  • model
  • address
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Copy a model instance

Create a copy of a model instance. Works in model inheritance case where ``instance.pk = None`` is not good enough, since the subclass instance refers to the parent_link's primary key during save. M2M relationships are currently not handled, i.e. they are not copied. See also Django #4027.

  • model
  • copy
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Class ModelInfo for show object info

This class works in compatibility with a ModelForm, but instead of show a form, it shows the field values. The Meta class attributes can be used to customize fields to show, to be excluded, to divide by sections, to urlize text fields, etc. **Example 1:** class InfoSingleCertificate(ModelInfo): class Meta: model = SingleCertificate sections = ( (None, ('vessel','description','document','comments','status',)), ('Issue', ('issue_date','issue_authority','issue_location',)), ) **Example 2:** class InfoSingleCertificate(ModelInfo): class Meta: model = SingleCertificate fields = ('vessel','description','document','comments','status', 'issue_date','issue_authority','issue_location',) **How to use:** Just save this snippet as a file in your project, import to your views.py module (or a new module named "info.py") and create classes following seemed sytax you use for ModelForms.

  • forms
  • model
  • display
  • modelforms
  • info
  • values
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Locking tables

Sometimes you need to prevent concurrent access to update/calculate some properties right. Here is (MySQL) specific example to lock one table with new object manager functions.

  • model
  • mysql
  • manager
  • table
  • lock
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Another means of updating a subset of a model's fields

Based on the UPDATE query section of `Model.save()`, this is another means of limiting the fields which are used in an UPDATE statement and bypassing the check for object existence which is made when you use `Model.save()`. Just make whatever changes you want to your model instance and call `update`, passing your instance and the names of any fields to be updated. Usage example: import datetime from forum.models import Topic from forum.utils.models import update topic = Topic.objects.get(pk=1) topic.post_count += 1 topic.last_post_at = datetime.datetime.now() update(topic, 'post_count', 'last_post_at') (Originally intended as a comment on [Snippet 479](/snippets/479/), but comments aren't working for me)

  • model
  • db
  • update
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shortcut for saving newforms to model

I come up with this short cut of saving data from newforms to a model, for newforms that contains attributes from several models or some attributes that doesn't found in a model attributes

  • newforms
  • model
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