模型实例参考

验证对象

There are four steps involved in validating a model:

1. 验证模型字段—— Model.clean_fields()
2. 验证整个模型—— Model.clean()
3. 验证字段的唯一性—— Model.validate_unique()
4. Validate the constraints - Model.validate_constraints()

All four steps are performed when you call a model's full_clean() method.

当你使用一个 ModelForm 时，调用 is_valid() 将对表单中包含的所有字段执行这些验证步骤。更多信息请参见 模型表单文档。只有当你打算自己处理验证错误，或者你从 ModelForm 中排除了需要验证的字段时，才需要调用模型的 full_clean() 方法。

Model.full_clean(exclude=None, validate_unique=True, validate_constraints=True)

This method calls Model.clean_fields(), Model.clean(), Model.validate_unique() (if validate_unique is True), and Model.validate_constraints() (if validate_constraints is True) in that order and raises a ValidationError that has a message_dict attribute containing errors from all four stages.

The optional exclude argument can be used to provide a set of field names that can be excluded from validation and cleaning. ModelForm uses this argument to exclude fields that aren't present on your form from being validated since any errors raised could not be corrected by the user.

请注意，当您调用模型的 save() 方法时，full_clean() 不会 自动调用。当你想为自己手动创建的模型运行一步模型验证时，你需要手动调用它。例如：

from django.core.exceptions import ValidationError
try:
    article.full_clean()
except ValidationError as e:
    # Do something based on the errors contained in e.message_dict.
    # Display them to a user, or handle them programmatically.
    pass

full_clean() 执行的第一步是清理每个单独的字段。

Model.clean_fields(exclude=None)

This method will validate all fields on your model. The optional exclude argument lets you provide a set of field names to exclude from validation. It will raise a ValidationError if any fields fail validation.

full_clean() 执行的第二步是调用 Model.clean()。这个方法应该被重写，以便对你的模型进行自定义验证。

Model.clean()

这个方法应该用来提供自定义模型验证，如果需要的话，还可以修改模型上的属性。例如，你可以使用它来自动为一个字段提供一个值，或进行需要访问多个字段的验证：

import datetime
from django.core.exceptions import ValidationError
from django.db import models
from django.utils.translation import gettext_lazy as _

class Article(models.Model):
    ...
    def clean(self):
        # Don't allow draft entries to have a pub_date.
        if self.status == 'draft' and self.pub_date is not None:
            raise ValidationError(_('Draft entries may not have a publication date.'))
        # Set the pub_date for published items if it hasn't been set already.
        if self.status == 'published' and self.pub_date is None:
            self.pub_date = datetime.date.today()

但请注意，像 Model.full_clean() 一样，当你调用你的模型的 save() 方法时，模型的 clean() 方法不会被调用。

在上面的例子中，由 Model.clean() 引发的 ValidationError 异常是用字符串实例化的，所以它将被存储在一个特殊的错误字典键中， NON_FIELD_ERRORS。这个键用于与整个模型相关的错误，而不是与某个特定字段相关的错误：

from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
try:
    article.full_clean()
except ValidationError as e:
    non_field_errors = e.message_dict[NON_FIELD_ERRORS]

要将异常分配给一个特定的字段，用一个字典实例化 ValidationError，其中键是字段名。我们可以更新前面的例子，将错误分配给 pub_date 字段：

class Article(models.Model):
    ...
    def clean(self):
        # Don't allow draft entries to have a pub_date.
        if self.status == 'draft' and self.pub_date is not None:
            raise ValidationError({'pub_date': _('Draft entries may not have a publication date.')})
        ...

如果你在 Model.clean() 期间检测到多个字段的错误，你也可以传递一个字段名与错误映射的字典：

raise ValidationError({
    'title': ValidationError(_('Missing title.'), code='required'),
    'pub_date': ValidationError(_('Invalid date.'), code='invalid'),
})

Then, full_clean() will check unique constraints on your model.

class Article(models.Model):
    ...
    def clean_fields(self, exclude=None):
        super().clean_fields(exclude=exclude)
        if self.status == 'draft' and self.pub_date is not None:
            if exclude and 'status' in exclude:
                raise ValidationError(
                    _('Draft entries may not have a publication date.')
                )
            else:
                raise ValidationError({
                    'status': _(
                        'Set status to draft if there is not a '
                        'publication date.'
                     ),
                })

Model.validate_unique(exclude=None)

This method is similar to clean_fields(), but validates uniqueness constraints defined via Field.unique, Field.unique_for_date, Field.unique_for_month, Field.unique_for_year, or Meta.unique_together on your model instead of individual field values. The optional exclude argument allows you to provide a set of field names to exclude from validation. It will raise a ValidationError if any fields fail validation.

UniqueConstraints defined in the Meta.constraints are validated by Model.validate_constraints().

请注意，如果你为 validate_unique() 提供了一个 exclude 参数，任何涉及你提供的一个字段的 unique_together 约束将不会被检查。

Finally, full_clean() will check any other constraints on your model.

Model.validate_constraints(exclude=None)

This method validates all constraints defined in Meta.constraints. The optional exclude argument allows you to provide a set of field names to exclude from validation. It will raise a ValidationError if any constraints fail validation.

其他模型实例方法

有几个对象方法有特殊用途。

from django.db import models

class Person(models.Model):
    first_name = models.CharField(max_length=50)
    last_name = models.CharField(max_length=50)

    def __str__(self):
        return '%s %s' % (self.first_name, self.last_name)

from django.db import models

class MyModel(models.Model):
    id = models.AutoField(primary_key=True)

class MyProxyModel(MyModel):
    class Meta:
        proxy = True

class MultitableInherited(MyModel):
    pass

# Primary keys compared
MyModel(id=1) == MyModel(id=1)
MyModel(id=1) != MyModel(id=2)
# Primary keys are None
MyModel(id=None) != MyModel(id=None)
# Same instance
instance = MyModel(id=None)
instance == instance
# Proxy model
MyModel(id=1) == MyProxyModel(id=1)
# Multi-table inheritance
MyModel(id=1) != MultitableInherited(id=1)

def get_absolute_url(self):
    return "/people/%i/" % self.id

def get_absolute_url(self):
    from django.urls import reverse
    return reverse('people-detail', kwargs={'pk' : self.pk})

def get_absolute_url(self):
    return '/%s/' % self.name

<!-- BAD template code. Avoid! -->
<a href="/people/{{ object.id }}/">{{ object.name }}</a>

<a href="{{ object.get_absolute_url }}">{{ object.name }}</a>