如何防止 Django 保存操作以避免对现有数据重复调用数据库

Question

我当前用于保存文章的代码保存新文章并打印 'The Post Already Exists!' 如果发现重复，但它仍在进行数据库调用，所以现在我的文章中有 ID 空白 table 因为重复文章未保存造成的误存。如果发现重复项以保持文章 ID 的一致性，我如何改进我的代码以防止保存操作？

if not Posts.objects.filter(title=post_title, slug=post_slug).exists():
   post = Posts(
        title = post_title,
        link = post_link,
        summary = post_summary,
        image_url = image_link,
        slug = post_slug,
        pub_date = date_published,
        guid = item.guid,
        feed_title = channel_feed_title,
        feed_link = channel_feed_link,
        feed_description = channel_feed_desc,
        source_id = selected_source_id,
        category_id = selected_category_id
       )
   post.save()

   for i in range(len(article_list)):
       post_tags = post.tags.add(article_list[i])

else:
   print("The Post Already Exists! Skipping...")

我一直收到这样的错误：

django.db.utils.IntegrityError: duplicate key value violates unique constraint "Posts_posts_slug_key" DETAIL:  Key (slug)=() already exists.

我的模型

class Categories(models.Model):
    category_name = models.CharField(max_length=500, verbose_name='Categories')
    date_created = models.DateField(auto_now_add=True, verbose_name='Date Created')
    last_modified = models.DateField(auto_now=True, verbose_name='Last Modified')

    def __str__(self):
        return f"{self.category_name}" 

    class Meta:
        verbose_name_plural = 'Categories'

class Source(models.Model):
    name = models.CharField(max_length=500, verbose_name='Website Name')
    feed_url = models.URLField(max_length=500, verbose_name='RSS Feed Link')
    date_created = models.DateField(auto_now_add=True, verbose_name='Date Created')
    last_modified = models.DateField(auto_now=True, verbose_name='Last Modified')

    def __str__(self):
        return f"{self.name}" 

    class Meta:
        verbose_name_plural = 'Feed Sources'

class Posts(models.Model):
    title = models.CharField(max_length=500, verbose_name='Post Title')
    link = models.URLField(max_length=500, verbose_name='Post Link')
    summary = models.TextField(verbose_name='Post Summary')
    image_url = models.URLField(max_length=500, null=True, verbose_name='Post Image URL')
    slug = models.SlugField(unique=True, max_length=500)
    tags = TaggableManager()
    pub_date = models.DateTimeField(verbose_name='Date Published')
    guid = models.CharField(max_length=500, verbose_name='Guid Code', null=True)
    feed_title = models.CharField(max_length=500, verbose_name='Feed Channel Title')
    feed_link = models.URLField(max_length=500, verbose_name='Feed Channel Link')
    feed_description = models.TextField(verbose_name='Feed Channel Description')
    date_created = models.DateField(auto_now_add=True, verbose_name='Date Created')
    last_modified = models.DateField(auto_now=True, verbose_name='Last Modified')
    source = models.ForeignKey(Source, on_delete=models.CASCADE, verbose_name='Source')
    category = models.ForeignKey(Categories, on_delete=models.CASCADE, verbose_name='Category')

    def __str__(self):
        return f"{self.title} - {self.feed_title}" 

    class Meta:
        verbose_name_plural = 'Posts'

Answer 1

由于您只有 slug 作为唯一字段，因此您必须检查是否已经存在具有相同 slug 的 post。如果没有，请创建它。您现在遇到的问题是您还检查了标题（作为 AND 运算符）。这可能会让您认为 post 不存在，但您仍然无法将其添加到数据库中，因为 slug 已经存在。但不是标题不同的鼻涕虫。这意味着您只需删除查询中的标题：

Posts.objects.filter(slug=post_slug).exists()

根据我之前的回答(https://docs.djangoproject.com/en/4.0/ref/models/querysets/#get-or-create)，这里还有一些解决问题的方法：

try:
    post = Posts.objects.get(slug=post_slug)
except Posts.DoesNotExist:
    post = Posts(title=post_title, link=...)
    post.save()

此处，对于并发请求，可能会多次尝试使用相同参数保存 Post。为了避免这种竞争条件，可以使用 get_or_create() 重写上面的示例，如下所示：

obj, created = Posts.objects.get_or_create(
    slug=post_slug,
    defaults={'title':post_title, 'link': ...},
)

如何防止 Django 保存操作以避免对现有数据重复调用数据库

How to prevent Django save action to avoid repetitive DB calls on already existing data

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duplicates