Articles in category: Django

Django application import and missed class_prepared signals.

11 August 2011 by Alexis Petrounias

Due to opaque application loading semantics within the Django i18n code, several model classes may be imported before a class_prepared signal listener connects, resulting in missing the signal entirely. Specifically, connecting to this signal from an application which appears first in INSTALLED_APPS, does not guarantee that it will execute when a class is first imported by any of the subsequent applications.

This problem is current as of Django 1.3 and has no generic solution as far as I know.
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Categories: Django

Propagating field changes in Django Model instance aliases

5 April 2010 by Alexis Petrounias

Django’s ORM creates multiple aliases for the same Model instance. In certain situations this may result in problematic behavior, as multiple operations on the same instance are interleaved, however, field access happens on different aliases of the instance, ultimately resulting in loss of updates. Read more »

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Categories: Django

Ordering on a field in the ‘through’ Model of a recursive ManyToMany relation in Django

6 February 2010 by Alexis Petrounias

It is not possible to order a Model on a field of the Model acting as the intermediate ‘through‘ of a ManyToMany relation in Django, because queries will not return items in the correct order, and in addition will include duplicate items, even when using .distinct().

This problem is current as of Django 1.3 and has no generic solution as far as I know.

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Duplicate items when ordering by Generic Relation in Django

27 January 2010 by Alexis Petrounias

When the optional ordering = … attribute of a model’s Meta class contains a GenericRelation from the Content Types framework in Django, there is no way to eliminate duplicate items being returned, even when using .distinct() (since .order_by(…) is applied by the ORM only after the SQL SELECT DISTINCT clause is built).

This problem is current as of Django 1.3 and has no generic solution as far as I know.

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Categories: Django