= Backwards-incompatible changes =

As Django is still in pre-1.0 mode, we haven't yet committed to maintaining backwards compatibility in any APIs. Although we're keeping such changes to a minimum, Django developers should be acutely aware of these changes.

Of course, once we reach 1.0, we'll be strongly committed to backward compatibility.

This page lists all backwards-incompatible changes to Django since the 0.95 release. For changes prior to 0.95, see the OlderBackwardsIncompatibleChanges page.

== Table of Contents ==

Changes made after Django [source:/django/tags/releases/0.95 0.95]:
 * August 2, 2006: [http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#Databaseconstraintnameschanged Database constraint names changed]
 * August 11, 2006: [http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#Backslashescapingchanged Backslash escaping changed]
 * September 27, 2006: [http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#RemovedENABLE_PSYCOsetting Removed ENABLE_PSYCO setting]
 * March 14, 2007: [http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#EnforcingMySQLdbversion Enforcing MySQLdb version]

Changes made after Django [source:/django/tags/releases/0.96 0.96]:

 * March 31, 2007: [http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#Changedspacelesstemplatetagtoremoveallspaces Changed 'spaceless' template tag to remove all spaces]
 * April 8, 2007: [http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#Renamedlocalflavor.usatolocalflavor.us Renamed `localflavour.usa` to `localflavor.us`]
 * April 9, 2007: [http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#RemovedLazyDate Removed `LazyDate`]


== Database constraint names changed ==

As of [3512], the format of the constraint names Django generates for foreign key references changed slightly. These names are only used sometimes, when it is not possible to put the reference directly on the affected column, so this is not always visible.

The effect of this change is that {{{manage.py reset app_name}}} and similar commands may generate SQL with invalid constraint names and thus generate an error when run against the database (the database server will complain about the constraint not existing). To fix this, you will need to tweak the output of {{{manage.py sqlreset app_name}}} to match the correct constraint names and pass the results to the database server manually.

== Backslash escaping changed ==

As of [3552], the Django database API now escapes backslashes given as query parameters. If you have any database API code that match backslashes, and it was working before (despite the broken escaping), you'll have to change your code to "unescape" the slashes one level.

For example, this used to work:

{{{
#!python
# Code that matches a single backslash
MyModel.objects.filter(text__contains='\\\\')
}}}

But it should be rewritten as this:

{{{
#!python
# Code that matches a single backslash
MyModel.objects.filter(text__contains='\\')
}}}

== Removed ENABLE_PSYCO setting ==

As of [3877], the {{{ENABLE_PSYCO}}} setting no longer exists. If your settings file includes {{{ENABLE_PSYCO}}}, nothing will break per se, but it just won't do anything. If you want to use [http://psyco.sourceforge.net/ Psyco] with Django, write some custom middleware that activates Psyco.

== Enforcing MySQLdb version ==

As of [4724], Django raises an error if you try to use the MySQL backend with a {{{MySQLdb}}} (MySQL Python module) version earlier than 1.2.1p2. There were significant, production-related bugs in earlier versions, so we have upgraded the minimum requirement.

In [4767], we added a {{{mysql_old}}} backend, which is identical to the {{{mysql}}} backend prior to the change in [4724]. You can use this backend if upgrading the {{{MySQLdb}}} module is not immediately possible. However, the {{{mysql_old}}} backend is deprecated, and  we will not continue developing it.

== Changed 'spaceless' template tag to remove all spaces ==

As of [4885], the {{{spaceless}}} template tag removes *all* spaces between HTML tags instead of preserving a single space.

For example, for this template code:
{{{
{% spaceless %}
<p>
    <a href="foo/">Foo</a>
</p>
{% endspaceless %}
}}}

The old output was this:

{{{
<p> <a href="foo/">Foo</a> </p>
}}}

The new output is this:

{{{
<p><a href="foo/">Foo</a></p>
}}}

As always, {{{spaceless}}} only affects space *between* HTML tags, not space within HTML tags or space in plain text.

== Renamed `localflavor.usa` to `localflavor.us` ==

As of [4954], `localflavor.usa` has been renamed `localflavor.us`. This change was made to match the naming scheme of other local flavors. 

== Removed `LazyDate` ==

The `LazyDate` helper class was removed in [4985]. Default field values and query arguments can both be callable objects, so instances of `LazyDate` can be replaced with a reference to a callable that evaluates to the current date (i.e., `datetime.now`). For example, the following model using `LazyDate`:

{{{
class Article(models.Model):
    title = models.CharField(maxlength=100)
    published = models.DateField(default=LazyDate())
}}}

can be redefined as:

{{{
from datetime import datetime
class Article(models.Model):
    title = models.CharField(maxlength=100)
    published = models.DateField(default=datetime.now)
}}}

Note that the new model definition refers to the name of the `datetime.now()` function, but doesn't actually call the function. The call to `datetime.now()` is deferred until the value is actually required (i.e., when the model is saved).