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

Thu 19 Nov 2015 Read More

Validation for full e-mails (e.g. "Joe Hacker <[email protected]>")

Out of the box, Django e-mail fields for both database models and forms only accept plain e-mail addresses. For example, `[email protected]` is accepted. On the other hand, full e-mail addresses which include a human-readable name, for example the following address fails validation in Django: Joe Hacker <[email protected]> This package adds support for validating full e-mail addresses. **Database model example** from django import models from full_email.models import FullEmailField class MyModel(models.Model): email = FullEmailField() **Forms example** from django import forms from full_email.formfields import FullEmailField class MyForm(forms.Form): email = FullEmailField(label='E-mail address') I maintain this code in a [GitHub gist](https://gist.github.com/1505228). It includes some unit tests as well.

• forms
• model
• email
• validation
• orm
• database

Wed 06 Feb 2013 Read More

Finding related objects for instances in a queryset

When deleting objects in Django's admin interface, it lists other objects which would be deleted and asks for confirmation. This snippet does the same programmatically. The snippet works in Django 1.3 (more specifically, revision 14507 or later). It uses Django internals which are not a part of the public API, so this might not work with future versions. Usage: `polls/models.py`: from django.db import models class Poll(models.Model): question = models.CharField(max_length=200) def __unicode__(self): return self.question class Choice(models.Model): poll = models.ForeignKey(Poll) choice = models.CharField(max_length=200) def __unicode__(self): return '%s %s' % (self.poll, self.choice) `$ ./manage.py shell` >>> from polls.models import Poll, Choice >>> from datetime import datetime >>> from pprint import pprint >>> poll1 = Poll.objects.create(question='Me?') >>> Choice.objects.create(poll=poll1, choice='Yes') >>> Choice.objects.create(poll=poll1, choice='No') >>> poll2 = Poll.objects.create(question='Really?') >>> Choice.objects.create(poll=poll2, choice='Yes') >>> Choice.objects.create(poll=poll2, choice='No') >>> pprint(get_related(Poll.objects.all())) {<class 'polls.models.Poll'>: [<Poll: Me?>, <Poll: Really?>], <class 'polls.models.Choice'>: [<Choice: Me? Yes>, <Choice: Me? No>, <Choice: Really? Yes>, <Choice: Really? No>]}

• db
• orm
• related

Thu 10 Mar 2011 Read More

StringField: CharField with no max_length for Postgres

Django's CharField requires a max_length, and TextField displays a multi- line widget, but in Postgres there's no reason to add an arbitrary max thanks to the `varlena` storage format. So this is a TextField that displays as a single line instead of a multiline TextArea.

• orm
• postgres
• charfield

Sun 05 May 2019 Read More

Remove a clause from a queryset

I want to create Mixins for QuerySet objects that will by default filter out certain records (e.g. filter out "deleted" records, or filter out "unapproved" records, etc). I'd like those to be separate independent mixins. So in each of those, I override all() to filter out deleted or unapproved, etc. But, I also want to offer a method in the queryset to remove those filters or remove some part of those filters. That's where this code comes in. After some examination of how QuerySets work, this seemed like the simplest method for "undoing" some filter in a queryset

• hack
• orm
• manager
• mixin
• queryset

Thu 16 Jul 2015 Read More

Enhance django postgresql orm for trigram search

This is a quite simple snippet to integrate postgresql trgm search in django 1.6.10 This snippet is easy to adapt to other special operators by changing the trgm_search function. This example uses the operator `%%` but you could use `ts_vector(fieldname) @@ to_tsquery(%s)`

• django
• orm
• postgresql
• trgm

Fri 03 Apr 2015 Read More

Circular reference with Django ORM and Postgres without breaking NOT NULL FK constraints

The recipe uses deferred constraint validation to create circular references across database tables. The example requires Postgres (MySQL doesn't support deferred constraints). To achieve this, the following is required: * Insertions must be performed in a transaction. Foreign key constraints will be validated at the end of the transactions, allowing for insertion of rows with FKs pointing to rows that don't exist yet. * Primary keys need to be generated before insertion. That's what `prefetch_id` does by pulling the next value from the `*_id_seq` sequence.

• django
• orm
• postgres

Thu 26 Mar 2015 Read More

MultiSelectField

This field provides a multi select choice field.

• fields
• orm

Sat 31 Mar 2012 Read More

make a combined set of db.Q objects out of a list of dicts and an operator

It's often useful to dynamically create filter criteria, and Q objects are useful for that, but sometimes you need to make a combined Q composed of various alternates. This bit of code eases the awkwardness of creating the first Q so that there's a combiner, plus the odd case of no criteria.

• orm
• filtering
• Q

Tue 24 Jan 2012 Read More

Django model objects and querysets dehydration/hydration

Dehydrates objects that can be dictionaries, lists or tuples containing django model objects or django querysets. For each of those, it creates a smaller/dehydrated version of it for saving in cache or pickling. The reverse operation is also provided so dehydrated objects can also be re-hydrated. *Example:* >>> import pickle >>> users = list(User.objects.all()[:20]) >>> print users [<User: Indiana Jones>, <User: Bilbo Baggins>, ...] >>> pickled_users = pickle.dumps(users) >>> print len(pickled_users) 17546 >>> dehydrated_users = dehydrate(users) >>> pickled_dehydrated_users = pickle.dumps(dehydrated_users) >>> rehydrated_users = hydrate(pickle.loads(pickled_dehydrated_users)) >>> print rehydrated_users [<User: Indiana Jones>, <User: Bilbo Baggins>, ...] >>> print len(pickled_dehydrated_users) 1471

• models
• orm
• queryset
• hydrate
• dehydrate

Thu 30 May 2013 Read More

See what depends on a given model

Riffing on http://djangosnippets.org/snippets/1024/ I didn't want a graph; I just wanted to see what depended on a specific model. This does that nicely.

• model
• orm
• dependency

Mon 14 Feb 2011 Read More

Improved Pickled Object Field (Fixed for Django 1.2)

Small changes to [Snippet 1694](http://djangosnippets.org/snippets/1694/) to that QueryAPI works for django 1.2 and higher. Changes: * Replaced `get_db_prep_value` with `get_prep_value`. * Replaced `get_db_prep_lookup` with modified `get_prep_lookup`.

• model
• db
• orm
• database
• pickle
• object
• field
• type
• pickled
• store

Wed 02 Feb 2011 Read More

orm_tools

This module contains classes that add new behavior to Django's ORM. Classes include: **Session** * Forces QuerySet objects to return identical instances when objects with the same primary key are queried. * Similar to [SQLAlchemy Session](http://www.sqlalchemy.org/docs/orm/session.html) **GraphSaver** * Save entire object graphs at once. * Automatically detects object dependencies and saves them in the correct order. **Collection** * Easier one-to-many relationships. Instructions and more information on [limscoder.com](http://www.limscoder.com/2011/01/django-orm-tools.html).

• session
• db
• orm

Sun 02 Jan 2011 Read More

Custom model field for mysql time type.

Django does not have a suitable model field can process time type in mysql, the DateTimeField built-in django can not process more than 24 hours. That's why the code born. **Simply usage** `from myapp.models import TimeAsTimeDeltaField, SECONDS_PER_MIN, SECONDS_PER_HOUR, SECONDS_PER_DAY class EstimatedTime: days = None hours = None minutes = None seconds = None class Case(models.Model): estimated_time = TimeAsTimeDeltaField(null=True, blank=True) def get_estimated_time(self): estimated_time = EstimatedTime() if self.estimated_time: total_seconds = self.estimated_time.seconds + (self.estimated_time.days * SECONDS_PER_DAY) days = total_seconds / SECONDS_PER_DAY hours = total_seconds / SECONDS_PER_HOUR - days * 24 minutes = total_seconds / SECONDS_PER_MIN - hours * 60 - days * 24 * 60 seconds = total_seconds % SECONDS_PER_MIN estimated_time.days = days estimated_time.hours = hours estimated_time.minutes = minutes estimated_time.seconds = seconds return estimated_time else: return estimated_time

• models
• orm
• database
• field
• timedelta

Sun 11 Jul 2010 Read More

UnicodeReprMixIn

Add's updated and created fields to a model if mixed in. Example that uses the name as the representation: class Company(models.Model, UnicodeReprMixIn): """ A representation of a comic book company. """ name = models.CharField(max_length=255) slug = models.SlugField() logo = models.ImageField(upload_to=os.path.join('upload', 'company_logos')) url = models.URLField(verify_exists=True) _unicode = "name"

• model
• unicode
• orm
• mixin
• __unicode__

Sun 11 Jul 2010 Read More