更新Django模型 [英] Updating django models

问题描述

我在现有模型中添加了一个新字段.当我使用命令"manage.py makemigrations myapp"时，出现以下错误:

I added a new field to an existing model. When I use the command "manage.py makemigrations myapp" I get the following error:

You are trying to add a non-nullable field 'slug' to post without a default. we can not do that < the database needs something to populate existing rows>. 

新字段段塞的默认值应该是什么?这是我的模型:

What should be the default value for the new field slug? Here is my model:

class Post(models.Model):
    title = models.CharField(max_length = 100, null = False, blank = False)
    body = models.TextField()
    dateCreated = models.DateTimeField(default=datetime.now, blank=True)
    slug = models.SlugField(unique = True)

    def __str__(self):
        return self.title

推荐答案

如果没有默认值，则不能将非空字段添加到现有模型中.如果必须将其设置为非空，则应该:

You cannot add a not-null field to an existing model without a default value. If you must make it not-null, you should:

1. 使用 null = True
添加字段
2. 迁移数据库
3. 填充现有行
4. 删除 null = True
5. 再次迁移

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