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https://github.com/hakib/django-admin-lightweight-date-hierarchy

Django Admin date_hierarchy with zero queries
https://github.com/hakib/django-admin-lightweight-date-hierarchy

django django-admin performance python python-2 python-3

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Django Admin date_hierarchy with zero queries

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README 

        
=======================================

Django Admin lightweight date hierarchy

=======================================



.. image:: https://badge.fury.io/py/django-admin-lightweight-date-hierarchy.svg

    :target: https://badge.fury.io/py/django-admin-lightweight-date-hierarchy



.. image:: https://github.com/hakib/django-admin-lightweight-date-hierarchy/actions/workflows/main.yml/badge.svg?branch=master

    :target: https://github.com/hakib/django-admin-lightweight-date-hierarchy/actions/workflows/main.yml?query=branch%3Amaster



.. image:: https://codecov.io/gh/hakib/django-admin-lightweight-date-hierarchy/branch/master/graph/badge.svg

    :target: https://codecov.io/gh/hakib/django-admin-lightweight-date-hierarchy



Django Admin date_hierarchy with zero queries

---------------------------------------------



**NOTE**: Some of the functionality provided by this extension is `included as

part of Django `_ starting at

version 2.1.



The built-in `date_hierarchy`_ tag performs a query to find the dates for which there is data.

On large tables this query can be very expensive.



To prevent additional queries, set ``date_hierarchy_drilldown = False`` on the ``ModelAdmin``.

When drill-down is disabled the tag will generate a default range of dates based solely

on the selected hierarchy level - without performing a query.



Default options for hierarchy levels:



- None - +-3 years from current year.

- Year - all months of the selected year.

- Month - all days of the selected month.



When ``date_hierarchy_drilldown = True`` or when not set the default behaviour is preserved.



.. _`date_hierarchy`: https://docs.djangoproject.com/en/1.11/ref/contrib/admin/#django.contrib.admin.ModelAdmin.date_hierarchy



Support

-------



Python>=3.7



Django 3.2, 4.2, >=5



Quickstart

----------



Install django-admin-lightweight-date-hierarchy::



    pip install django-admin-lightweight-date-hierarchy



Add it to your ``INSTALLED_APPS``:



.. code-block:: python



    INSTALLED_APPS = (

        ...

        'django_admin_lightweight_date_hierarchy',

        ...

    )



Add the following to any ``ModelAdmin`` with ``date_hierarchy`` to prevent the default drill-down behaviour:



.. code-block:: python



    @admin.register(MyModel)

    class MyModelAdmin(admin.ModelAdmin):

        date_hierarchy = 'created'

        date_hierarchy_drilldown = False



To change the default dates generated by the template tag for any level in the hierarchy, implement a

function called ``get_date_hierarchy_drilldown(self, year_lookup=None, month_lookup=None)`` on the ``ModelAdmin``.

The function receives the date hierarchy filter and is expected to return a list of dates to offer for drill-down.



For example, a custom drill-down that offers only past dates:



.. code-block:: python



    import datetime

    import calendar



    from django.utils import timezone

    from django.contrib import admin



    @admin.register(MyModel)

    class MyModelAdmin(admin.ModelAdmin):

        date_hierarchy = 'created'

        date_hierarchy_drilldown = False



        def get_date_hierarchy_drilldown(self, year_lookup, month_lookup):

            """Drill-down only on past dates."""



            today = timezone.now().date()



            if year_lookup is None and month_lookup is None:

                # Past 3 years.

                return (

                    datetime.date(y, 1, 1)

                    for y in range(today.year - 2, today.year + 1)

                )



            elif year_lookup is not None and month_lookup is None:

                # Past months of selected year.

                this_month = today.replace(day=1)

                return (

                    month for month in (

                        datetime.date(int(year_lookup), month, 1)

                        for month in range(1, 13)

                    ) if month <= this_month

                )



            elif year_lookup is not None and month_lookup is not None:

                # Past days of selected month.

                days_in_month = calendar.monthrange(year_lookup, month_lookup)[1]

                return (

                    day for day in (

                        datetime.date(year_lookup, month_lookup, i + 1)

                        for i in range(days_in_month)

                    ) if day <= today

                )



Blog Post

---------



More about the process of developing date hierarchy drill-down in this blog post `scaling django admin date hierarchy`_.



.. _`scaling django admin date hierarchy`: https://hakibenita.com/scaling-django-admin-date-hierarchy



RangeBasedDateHierarchyListFilter

---------------------------------



Django filters the queryset for a given level in the date hierarchy using a database

function to extract the relevent date part. For example, when filtering a queryset on

a ``created`` date field for November 2017, Django will execute the following query:



.. code-block:: sql



    SELECT

        ...

    FROM

        app_model

    WHERE

        created BETWEEN '2017-01-01 00:00:00' AND '2017-12-31 23:59:59.999999'

        AND EXTRACT('month', created) = 11



A function is opaque to the database optimizer. If you have a range-based (btree) index

on the field, using EXTRACT does not limit the range at all, and so the index is not

utilized properly which might lead to a sub optimal execution plan.



There are several approaches to tackle this issue. For example, in databases that support

function based indexes the developer can add an index on the specific function to try and

improve the performace of the query. The downside to this approach is having to maintain

additional indexes for each level of the hierarchy. Additional indexes slow down insert

and update operations, and take up space.



Another approach is to simplify the condition used by Django to filter the queryset

for any given level in the hierarchy:



.. code-block:: sql



    SELECT

        ...

    FROM

        app_model

    WHERE

        created >= '2017-11-01 00:00:00'

        AND created < '2017-12-01 00:00:00'



This is what ``RangeBasedDateHierarchyListFilter`` does.



To achieve the above query, add the following to your ModelAdmin:



.. code-block:: python



    from django.contrib import admin

    from django_admin_lightweight_date_hierarchy.admin import RangeBasedDateHierarchyListFilter



    @admin.register(MyModel)

    class MyModelAdmin(admin.ModelAdmin):

        date_hierarchy = 'created'



        list_filter = (

            RangeBasedDateHierarchyListFilter,

        )



Blog Post

----------



More about the motivation and the performace of ``RangeBasedDateHierarchyListFilter`` in this blog post `Django Admin Range-Based Date Hierarchy`_.



.. _`Django Admin Range-Based Date Hierarchy`: https://codeburst.io/django-admin-range-based-date-hierarchy-37955b12ea4e



Running Tests

-------------



::



    source /bin/activate

    (venv) $ pip install tox

    (venv) $ tox