From cf78a0ccc39902f73a1e1540b59c3b6c89aa51f6 Mon Sep 17 00:00:00 2001 From: Markus Holtermann Date: Wed, 24 Sep 2014 19:07:56 +0200 Subject: [PATCH] [1.7.x] Fixed #23473 -- Documented that @deconstructible classes need __eq__. Backport of 066e672d79 from master --- docs/topics/migrations.txt | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/docs/topics/migrations.txt b/docs/topics/migrations.txt index 685c716f3c..3f00dec80a 100755 --- a/docs/topics/migrations.txt +++ b/docs/topics/migrations.txt @@ -594,9 +594,14 @@ of three things ``(path, args, kwargs)``: Django will write out the value as an instantiation of your class with the given arguments, similar to the way it writes out references to Django fields. +To prevent a new migration from being created each time +:djadmin:`makemigrations` is run, you should also add a ``__eq__()`` method to +the decorated class. This function will be called by Django's migration +framework to detect changes between states. + As long as all of the arguments to your class' constructor are themselves -serializable, you can just use the ``@deconstructible`` class decorator -from ``django.utils.deconstruct`` to add the method:: +serializable, you can use the ``@deconstructible`` class decorator from +``django.utils.deconstruct`` to add the ``deconstruct()`` method:: from django.utils.deconstruct import deconstructible @@ -604,8 +609,13 @@ from ``django.utils.deconstruct`` to add the method:: class MyCustomClass(object): def __init__(self, foo=1): + self.foo = foo ... + def __eq__(self, other): + return self.foo == other.foo + + The decorator adds logic to capture and preserve the arguments on their way into your constructor, and then returns those arguments exactly when deconstruct() is called.