在Django 1.9中，使用JSONField（native postgres jsonb）的约定是什么？ [英] In Django 1.9, what's the convention for using JSONField (native postgres jsonb)?

问题描述

Django 高度建议 不使用 null = True for CharField和TextField基于字符串的字段，以便不具有no data的两个可能值（假设您允许空字符串为空白=真）。这对我来说非常有意义，我在所有的项目中都这样做。

Django highly suggests not to use null=True for CharField and TextField string-based fields in order not to have two possible values for "no data" (assuming you're allowing empty strings with blank=True). This makes total sense to me and I do this in all my projects.

Django 1.9引入了 JSONField ，它使用底层的Postgres jsonb 数据类型。上述建议是否应使用JSONField（即 blank = True 而不是 null = True ）？或者，应该使用 null = True ？或者，应该使用 default = dict ？要么， ..？为什么？

Django 1.9 introduces JSONField, which uses the underlying Postgres jsonb data type. Does the suggestion above carry over to JSONField (i.e. blank=True should be used instead of null=True)? Or, should null=True be used instead? Or, should default=dict be used instead? Or, ..? Why?

换句话说，当您只允许一个无数据值时，新的本机JSONField的约定是什么？请支持你的答案，因为我做了大量的研究，找不到任何官方的。感谢提前。

In other words, what is the convention for the new native JSONField, when you want to allow only one "no data" value? Please support your answer because I did a lot of research and couldn't find anything official. Thanks in advance.

推荐答案

Django代码暗示的约定似乎是将而不是一个空字符串（如 CharField 的惯例）。我这样说是因为以下原因：

The convention implied from the Django code seems to be to store null JSON values as NULL as opposed to as an empty string (as is the convention for the CharField). I say this because of the following:

empty_strings_allowed 继承自 Field CharField ，并设置为 True ：

The empty_strings_allowed is inherited from Field in CharField, and is set to True:

django / db /模型/字段/ __ init __。py＃L96

class Field(RegisterLookupMixin):
    """Base class for all field types"""

    # Designates whether empty strings fundamentally are allowed at the
    # database level.
    empty_strings_allowed = True
    ...

JSONField ，但是用 False 覆盖：

django / contrib / postgres / fields / jsonb.py＃L13

class JSONField(Field):
    empty_strings_allowed = False
    ...

这导致 CharField 的默认值为和 JSONField 到无当您实例化模型而不显式传递这些字段的值。

This causes CharField's to default to "" and JSONField's to None when you instantiate a model without explicitly passing the values for these fields.

django / db / models / fields / init .py＃L791

django/db/models/fields/init.py#L791

def get_default(self):
    """
    Returns the default value for this field.
    """
    if self.has_default():
        if callable(self.default):
            return self.default()
        return self.default
    if (not self.empty_strings_allowed or (self.null and
               not connection.features.interprets_empty_strings_as_nulls)):
        return None
    return ""

因此，如果要制作一个 JSONField 可选，则必须使用：

Therefore, if you want to make a JSONField optional, you have to use:

json_field = JSONField(blank=True, null=True)

如果您只使用 blank = True ，就像 CharField 一样，尝试运行 MyModel.objects.create（...）而不传递<$ c时，会得到一个 IntegrityError $ c> json_field 参数显式。

If you use only blank=True, as you would for CharField, you'll get an IntegrityError when trying to run MyModel.objects.create(...) without passing a json_field argument explicitly.

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