django-generate-series

Use Postgres' generate_series to create sequences with Django's ORM

https://django-generate-series.readthedocs.io/

Goals

When using Postgres, the set-returning functions allow us to easily create sequences of numbers, dates, datetimes, etc. Unfortunately, this functionality is not currently available within the Django ORM.

This project makes it possible to create such sequences, which are returned as a Django QuerySet. For instance, assuming you have an Order model, you can create a set of sequential dates and then annotate each with the number of orders placed on that date. This will ensure you have no date gaps in the resulting QuerySet. To get the same effect without this package, additional post-processing of the QuerySet with Python would be required.

New in version 1.0.0: you can now generate cartesian products with a QuerySet or an iterable. For instance, you can create a sequence of dates that are repeated for each item in a QuerySet or iterable.

Terminology

Although this packages is named django-generate-series based on Postgres' generate_series set-returning function, mathematically we are creating a sequence rather than a series.

• sequence: Formally, "a list of objects (or events) which have been ordered in a sequential fashion; such that each member either comes before, or after, every other member."

  In django-generate-series, we can generate sequences of integers, decimals, dates, datetimes, as well as the equivalent ranges of each of these types.

• term: The nth item in the sequence, where 'nth' can be found using the id of the model instance.

  This is the name of the field in the model which contains the term value.

API

The package includes a generate_series function from which you can create your own series-generating QuerySets. The field type passed into the function as output_field determines the resulting type of series that can be created. (Thanks, @adamchainz for the format suggestion!)

generate_series keyword arguments

• start - The value at which the sequence should begin (required)
• stop - The value at which the sequence should end. For range types, this is the lower value of the final term (required)
• step - How many values to step from one term to the next. For range types, this is the step from the lower value of one term to the next. (required for non-integer types)
• span - When generating a sequence of ranges (except for date and datetime ranges), this specifies the difference between the lower value of each term and its upper value. Typically, this is the same as the step value. (optional, defaults to 1 if neeeded in the query)
• output_field - A django model field class, one of BigIntegerField, IntegerField, DecimalField, DateField, DateTimeField, BigIntegerRangeField, IntegerRangeField, DecimalRangeField, DateRangeField, or DateTimeRangeField. If not provided, the field will be determined from the type of the start input. (optional)
• include_id - If set to True, an auto-incrementing id field will be added to the QuerySet.
• max_digits - For decimal types, specifies the maximum digits.
• decimal_places - For decimal types, specifies the number of decimal places.
• default_bounds - In Django 4.1+, allows specifying bounds for list and tuple inputs. See Django docs
• queryset - If provided, each pk in the QuerySet will be combined with the generated series as the cartesian product. This is useful for creating a series that is repeated for each pk in the QuerySet. (optional, only one of queryset or iterable can be provided)
• iterable - If provided, the iterable will be combined with the generated series as the cartesian product. This is useful for creating a series that is repeated for each item in the iterable. (optional, only one of queryset or iterable can be provided)

generate_series return value

The function returns a QuerySet of the specified type. The QuerySet will have a term field that contains the sequence values. If include_id is set to True, the QuerySet will also have an id field that contains the sequence values. Finally, if queryset or iterable is provided, the QuerySet will have a value field that contains the primary key values from the provided QuerySet or the items in the provided iterable.

Basic Examples

Create a bunch of sequential integers

from django.db import models
from django_generate_series.models import generate_series

integer_sequence_queryset = generate_series(
    start=0, stop=1000, output_field=models.IntegerField,
)

for item in integer_sequence_queryset:
    print(item.term)

Result:

term
----
0
1
2
3
4
5
6
7
8
9
10
...
1000

generate_series returns a QuerySet!

Keep in mind that generate_series returns a QuerySet, so you can chain the result with other QuerySet methods, use it in subqueries, filter it, etc. For instance, continuing from the previous example:

for item in integer_sequence_queryset.filter(term__lt=5):
    print(item.term)

Result:

term
----
0
1
2
3
4

Create a sequence of dates from now until a year from now

from django.db import models
from django.utils import timezone
from django_generate_series.models import generate_series

now = timezone.now().date()
later = (now + timezone.timedelta(days=365))

date_sequence_queryset = generate_series(
    start=now, stop=later, step="1 days", output_field=models.DateField,
)

for item in date_sequence_queryset:
    print(item.term)

Result:

term
----
2022-04-27
2022-04-28
2022-04-29
2022-04-30
2022-05-01
2022-05-02
2022-05-03
...
2023-04-27

Note: See the usage examples in the docs and the example project in the tests directory for further examples of usage.

Usage with partial

If you often need sequences of a given field type or with certain args, you can use partial.

Example with default include_id and output_field values:

from functools import partial

int_and_id_series = partial(generate_series, include_id=True, output_field=BigIntegerField)

qs = int_and_id_series(1, 100)