#booleanfield

[guangyaw]

Django3.0 正式 Release

Django 3.0 在 2019/12/02 正式釋出，

發布了許多新功能以外，

對於舊有的 Python 2 也不予支持，

當然第三方的支持還是能用的，

需要更詳細的 release note 可到官方網站觀看

此處僅列出幾個要點。

而官方網站也同時釋出了 Django 2.2.8 ，

此版本同時也是 Django 2.2 的最後錯誤修正版本

底下為官方釋出的更新時程表：

Django 3.0 的主要變更有：

對 ASGI 的支持讓 Djano 具有完整的異步功能

正式支援 MariaDB 10.1 及更新版本

輸出BooleanField的表達式，可以直接在QuerySet過濾器中使用

次要的變更：

django.contrib.admin：

在…

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[yummycoding]

Reminder: after Django 1.5, default value for BooleanField is None, not False!

It's mentioned explicitly in the Django 1.6 release docs but still caught me by surprise: the default value for django.db.models.BooleanField is now None not False. This means that if the corresponding field in your database is something like tinyint not null default 0 you will encounter an error on record creation like:

Cannot insert the value NULL into column 'some_truefalse_value', table 'db.dbo.Foo'; column does not allow nulls. INSERT fails.

That's because Django explicitly inserts values for all columns, even ones it does not have data for, and where before the value was False which rendered as 0 in the SQL query, it is now None which renders as NULL.

The Django developers explain the change thusly:

In previous version of Django, it was False, but that didn’t represent accurately the lack of a value.

I disagree with this decision on the part of the Django developers, because:

there is already a NullBooleanField field type which covers boolean values with an optional "No Value".

it is reasonable to consider that for a data type in which the only possible values are true and false that the absence of a value equates to false — particularly in the context of a language where None and blank are considered falsey.

it requires users to make changes everywhere in their code, and rely on the developers of the libraries they use to make similar changes

Personally, I think that when it comes to a determination whether a change should be made to a section of code, "will break existing behavior" should trump "is very slightly ideologically inconsistent".

Also, you want to talk about inconsistent?

The default/empty value for django.forms.fields.BooleanField is False! That's because, if it wasn't, when a checkbox was left unchecked the value in the corresponding field would be None. As far as I can tell, BooleanField is the only field for which the default value of the form Field is different than the default value for the model Field.

So I will now be wasting time going through all of my code and adding default=False to all BooleanFields in my code. And I will either be looking for updates of libraries I am using that make use of BooleanFields, or modifying my existing installs.

BTW, I upgraded from 1.5 to 1.7 (now that 1.5 is officially no longer supported) and this change was not listed on the "deprecation timeline" which states that it "outlines when various pieces of Django will be removed or altered in a backward incompatible way. Changing False to None is a backwards incompatible change. There were no warnings of this change in the 1.5 release. The only place that mentions the change is the release notes for 1.6. That means that developers like me, who wrote prior code based on established behavior, will not discover this change unless they make a practice of reading all past release notes when upgrading, or until it causes an error when the code is updated.

The ticket in question Apparently this has been in the works since Django 1.3!