Django QuerySet API 检查这个 id 是否唯一

Question

这是我的模型的样子：

class Catalog(models.Model):
    global_id = models.IntegerField(unique=True)
    name = models.CharField(max_length=30)
    short_name = models.CharField(max_length=10)
    description = models.CharField(max_length=200, blank=True)
    version = models.CharField(max_length=10)

    class Meta:
        constraints = [
            models.CheckConstraint(
                check=models.Q(
                //
                CHECK IF VERSION IS UNIQUE FOR THIS PARTICULAR GLOBAL_ID
                //
                ),
                name="%(app_label)s_%(class)s_unique_version",
            )
        ]

如您所见，我需要确保版本模型对于特定 global_id 是唯一的，我只是不知道该怎么做。帮助。

Answer 1

下面的代码允许您对这两个字段设置唯一约束。请注意，要使其起作用，请从 global_id 字段中删除唯一约束。

class Catalog(models.Model):
    global_id = models.IntegerField(max_length=10)
    version = models.CharField(max_length=10)

    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=['global_id', 'version'],
                name='unique_global_id_for_version'
            )
        ]

>>> Catalog.objects.create(global_id=80, version=80)
<Catalog: Catalog object (10)>
>>> Catalog.objects.create(global_id=90, version=80)
<Catalog: Catalog object (11)>
>>> Catalog.objects.create(global_id=80, version=80)
django.db.utils.IntegrityError: UNIQUE constraint failed: ...
>>> Catalog.objects.create(global_id=80, version=90)
<Catalog: Catalog object (12)>

上面，当尝试创建带有 global_id=80 的目录时失败了，因为它已经存在于 version=80，但后来可以为目录创建带有 global_id=80 的目录version=90.

The docs for this constraint

Answer 2

根据 the docs，您可以使用 django 3.1 的“唯一”选项：

If True, this field must be unique throughout the table.

This is enforced at the database level and by model validation. If you try to save a model with a duplicate value in a unique field, a django.db.IntegrityError will be raised by the model’s save() method.

这将使您的声明像这样：

version = models.CharField(max_length=10, unique=True)

Django QuerySet API 检查这个 id 是否唯一

Django QuerySet API check if is unique for this id

django

django-models

django-queryset