django-annotatable-properties 0.1.4

A Django app that allows annotating properties on querysets.

Annotatable Properties

Annotatable properties is a django library that allows you to annotate any model property or calculated value using property name, lambdas or any other callable.

It is approximately 15x slower than regular Django ORM, but it is still fast enough for most use cases.

Quick start

1. Install using pip

   pip install django-annotatable-properties
   

2. Set the desired model's manager to AnnotatableQuerySet.as_manager() or AnnotatableManager():

   from annotatable_properties import AnnotatableManager
   
   
   class SomeModel(models.Model):
       ...
       @property
       def some_field_plus_one(self):
           return self.some_field + 1
       ...
       objects = AnnotatableManager(),
   

3. Now you can annotate any model property or calculated value using property name, lambdas or any other callable:

   from some_app.models import SomeModel
   SomeModel.objects.annotate_property('some_field_plus_one').filter(some_field_plus_one_property__gt=10)
   

   is roughly equivalent to:

   from some_app.models import SomeModel
   from django.db.models import F
   SomeModel.objects.annotate(some_field_plus_one_property=F('some_field') + 1).filter(some_field_plus_one_property__gt=10)
   

How It Works

Annotatable properties make annotating anything possible and much easier compared to the standard Django ORM. It basically converts the QuerySet annotated into a Python sequence, calculates the values to be annotated and annotates using raw SQL, then converts the result back to a QuerySet, keeping the order of the original QuerySet.

Some More Usage Examples

Sort method

1. Assume we have a model, Book, that has a title field, which is a CharField and all titles end with a number (from 0-9 to keep the example simple). We are required to order the Book QuerySet that we have by the number at the end of the title. If the Book is using the AnnotatableManager as the manager or the AnnotatableQuerySet as the QuerySet, we can do the following:

   from book_app.models import Book
       
   Book.objects.sort(key=lambda book: book.title[-1])
   

2. Assume we have another model, Author, that has a name field, which is a CharField We want to sort all the authors by the length of their name and then by their name. If the Author is using the AnnotatableManager as the manager or the AnnotatableQuerySet as the QuerySet, we can do the following:

   from author_app.models import Author
       
   Author.objects.sort(key=lambda author: (len(author.name), author.name))
   

3. Assume we have the same Author model from example 2. But this time, the model has a property called name_length, which is the length of the name field. Something like:

   from django.db import models
       
   class Author(models.Model):
       name = models.CharField(max_length=100)
       ...
       @property
       def name_length(self):
           return len(self.name)
   

   We want to sort all the authors by the length of their name. This can be done by:

   from author_app.models import Author
       
   Author.objects.sort(key='name_length')
   

   or if we want to sort by name_length and then name, we can use:

   from author_app.models import Author
       
   Author.objects.sort(key=('name_length', 'name'))
   

annotate_property method

1. Assume we have a model, Book, that has a title field, which is a CharField and all titles end with a number (from 0-9 to keep the example simple). We are required to annotate the Book QuerySet that we have with the number at the end of the title. If the Book is using the AnnotatableManager as the manager or the AnnotatableQuerySet as the QuerySet, we can do the following:

   from book_app.models import Book
       
   books = Book.objects.annotate_property(lambda x: x.title[-1], property_name='title_number')
   

   Then if we wanted to exclude all the books that have a title number of 0, we can do:

   books.exclude(title_number=0)
   

2. Assume we have an Author model. The model has a property called name_length, which is the length of the name field. Something like:

   from django.db import models
       
   class Author(models.Model):
       name = models.CharField(max_length=100)
       ...
       @property
       def name_length(self):
           return len(self.name)
   

   To annotate this, we can simply do:

   from author_app.models import Author
       
   authors = Author.objects.annotate_property('name_length')
   

   Then if we wanted to exclude all the authors that have a name shorter than 5 characters, we can do:

   authors.exclude(name_length_property__lt=5)
   

   • Note that when the property name parameter is omitted, the property name is automatically appended with _property to avoid conflicts with the actual property.
   • Property annotations can be chained, just like ORM queries.