在可以使用这种多对多关系之前，“<Post:>”字段需要有一个值 "id"

Question

当我尝试通过 django admin 添加 Post 时出现错误，我尝试添加的 Post 需要具有字段 ID 值。你知道为什么吗？

now = datetime.now()

class Category(models.Model):
    name = models.CharField(max_length=200)
    slug = models.SlugField(unique=True)

    class Meta:
        verbose_name_plural = "categories"

    def __str__(self):
        return self.name


class Post(models.Model):
    title = models.CharField(max_length=100)
    excerpt = models.CharField(max_length=200)
    main_image = models.ImageField()
    author = models.ForeignKey(users.models.CustomUser, on_delete=models.CASCADE, related_name='blog_posts', null=True)
    content = models.TextField(null=True)
    created_at = models.DateTimeField(editable=False)
    updated_at = models.DateTimeField(editable=False)
    category = models.ManyToManyField(Category, related_name='post_category')

    class Meta:
        ordering = ['-created_at']

    def save(self, *args, **kwargs):
        if not self.id:
            self.created_at = now
        self.updated_at = now

    def __str__(self):
        return self.title

Answer 1

您需要拨打 super().save(*args, **kwargs) 电话。此外，使用常量不会起作用：这将分配您启动服务器的时间，而不是当前时间，因此：

from django.utils.timezone import <b>now</b>

class Post(models.Model):
    # …

    def save(self, *args, **kwargs):
        if not self.id:
            self.created_at = <strong>now()</strong>
        self.updated_at = <strong>now()</strong>
        <strong>super().save(*args, **kwargs)</strong>

您还不需要指定更新 created_at 和 updated_at 字段的逻辑，您可以使用 auto_now_add=True [Django-doc] and auto_now=True [Django-doc]:

class Post(models.Model):
    # …
    created_at = models.DateTimeField(<strong>auto_now_add=True</strong>)
    updated_at = models.DateTimeField(<strong>auto_now=True</strong>)
    # …

    class Meta:
        ordering = ['-created_at']

    # no save override

    def __str__(self):
        return self.title

在可以使用这种多对多关系之前，“<Post:>”字段需要有一个值 "id"

"<Post:>" needs to have a value for field "id" before this many-to-many relationship can be used

django

django-models