Django model filter with validate_unique()

在 Django 中使用 validate_unique() 方法时，遇到 “invalid syntax” 的错误。

代码如下：

class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    is_joined = models.BooleanField(default=False)  # if True, joined, else wish_member
    is_master = models.BooleanField(default=False)

    def __str__(self):
        if (self.is_joined):
            return self.person.name + " is a member in Group " + self.group.name
        return self.person.name + " wishes to join in Group " + self.group.name

    def validate_unique(self, *args, **kwargs):
        # super(Person, self.person).validate_unique(*args, **kwargs)
        # tests if there is already the same person in the same group.
        if (self.__class__.objects.filter(person_id=self.person.id, group_id=self.group.id,).exists()):
            raise ValidationError(
                {
                    NON_FIELD_ERRORS:
                        ('The person already exists.',)
                }
            )
        elif (self.__class__objects.filter(is_master=True, group_id=self.group.id,).exists()):
            raise ValidationError(
                {
                    NON_FIELD_ERRORS:
                        ('The master already exists.')
                })

# Edits: noticed the dot missing.leaving it there for the credit who found it.
# Error occurs in:
# elif(self.__class__.objects.filter(is_master = True, group_id = self.group.id,).exists()):

2. 解决方案：

1. 语法错误

在 validate_unique() 方法中，elif (self.__class__objects.filter(is_master=True, group_id=self.group.id,).exists()): 这行代码中，__class__objects 写成了 __class__.objects。

正确的代码如下：

class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    is_joined = models.BooleanField(default=False)  # if True, joined, else wish_member
    is_master = models.BooleanField(default=False)

    def __str__(self):
        if (self.is_joined):
            return self.person.name + " is a member in Group " + self.group.name
        return self.person.name + " wishes to join in Group " + self.group.name

    def validate_unique(self, *args, **kwargs):
        # super(Person, self.person).validate_unique(*args, **kwargs)
        # tests if there is already the same person in the same group.
        if (self.__class__.objects.filter(person_id=self.person.id, group_id=self.group.id,).exists()):
            raise ValidationError(
                {
                    NON_FIELD_ERRORS:
                        ('The person already exists.',)
                }
            )
        elif (self.__class__.objects.filter(is_master=True, group_id=self.group.id,).exists()):
            raise ValidationError(
                {
                    NON_FIELD_ERRORS:
                        ('The master already exists.')
                })

2. 使用 unique_together

也可以使用 unique_together 选项来实现类似的功能。

在 Membership 模型中添加如下代码：

class Meta:
    unique_together = (
        ("person", "group"),
        ("is_master", "group"),
    )

这样，person 和 group 的组合以及 is_master 和 group 的组合都将是唯一的。

3. 自定义 validate_unique() 方法

还可以自定义 validate_unique() 方法来实现类似的功能。

class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    is_joined = models.BooleanField(default=False)  # if True, joined, else wish_member
    is_master = models.BooleanField(default=False)

    def __str__(self):
        if (self.is_joined):
            return self.person.name + " is a member in Group " + self.group.name
        return self.person.name + " wishes to join in Group " + self.group.name

    def validate_unique(self, *args, **kwargs):
        # Check if the person is already a member of the group
        if self.__class__.objects.filter(person=self.person, group=self.group).exists():
            raise ValidationError(
                {
                    NON_FIELD_ERRORS:
                        ('The person is already a member of the group.')
                }
            )

        # Check if there is already a master for the group
        if self.__class__.objects.filter(is_master=True, group=self.group).exists():
            raise ValidationError(
                {
                    NON_FIELD_ERRORS:
                        ('There is already a master for the group.')
                }
            )

这样，也可以实现 person 和 group 的组合以及 is_master 和 group 的组合都是唯一的。

根据你的具体需求，可以选择其中一种方法来实现。