Django每次执行makemigrations重复生成迁移文件的问题

问题背景 #

我的应用中有如下模型：

class PutAwayProductsPosition(models.Model):
    products = models.ForeignKey(Product, on_delete=models.CASCADE)
    put_position = models.CharField(max_length=50, default=0)
    is_put = models.BooleanField(default=False)


class PutAway(models.Model):
    warehouse = models.ForeignKey(Warehouse, on_delete=models.CASCADE)
    grn = models.ForeignKey("grn.GRN", on_delete=models.CASCADE)
    employee_assigned = models.ForeignKey(Employee, on_delete=models.CASCADE)
    putaway_id = models.IntegerField(default=0)
    products_position = models.ManyToManyField(PutAwayProductsPosition)
    completely_executed = models.BooleanField(default=False)
    partially_executed = models.BooleanField(default=False)
    created = models.DateTimeField(auto_now_add=True)
    scheduled_datetime = models.DateTimeField(auto_now_add=True)
    owner = models.ForeignKey(User, on_delete=models.CASCADE)

每次执行makemigrations时，都会自动生成如下迁移文件，即使模型没有任何修改：

class Migration(migrations.Migration):

    dependencies = [
        ('grn', '0068_auto_20230411_0703'),
        ('putpick', '0033_auto_20230410_0810'),
    ]

    operations = [
        migrations.AlterField(
            model_name='putaway',
            name='grn',
            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='grn.GRN'),
        ),
    ]

我尝试使用--fake迁移解决，但问题依旧，操作过程及输出如下：

(venv) rahulsharma@Rahuls-MacBook-Air Trakkia-Backend % python manage.py migrate --fake putpick 0034_auto_20230411_0703   
Operations to perform:
  Target specific migration: 0034_auto_20230411_0703, from putpick
Running migrations:
  No migrations to apply.
  Your models have changes that are not yet reflected in a migration, and so won't be applied.
  Run 'manage.py makemigrations' to make new migrations, and then re-run 'manage.py migrate' to apply them.
(venv) rahulsharma@Rahuls-MacBook-Air Trakkia-Backend % python manage.py makemigrations                                
Migrations for 'grn':
  grn/migrations/0069_auto_20230411_0828.py
    - Alter field grn on grntempscans
Migrations for 'putpick':
  putpick/migrations/0035_auto_20230411_0828.py
    - Alter field grn on putaway
(venv) rahulsharma@Rahuls-MacBook-Air Trakkia-Backend % python manage.py migrate                                       
Operations to perform:
  Apply all migrations: all apps name
Running migrations:
  Applying grn.0069_auto_20230411_0828... OK
  Applying putpick.0035_auto_20230411_0828... OK

现在再次运行makemigrations，仍会重复生成这两个迁移文件。

问题原因 #

这种重复生成迁移的核心原因是Django的迁移检测机制无法正确识别外键引用的一致性，常见触发场景包括：

1. 跨应用外键使用字符串引用（"grn.GRN"）时，Django解析字符串的逻辑与直接导入模型的检测逻辑存在隐性差异
2. 关联应用（grn）的迁移也在修改相关字段，导致迁移依赖关系出现循环检测
3. 迁移缓存或历史记录存在异常，导致Django误判模型与数据库 schema 不一致

解决方法 #

1. 统一外键引用方式（优先推荐） #

将模型中的字符串引用改为直接导入的方式，避免字符串解析带来的检测偏差：

# 先从grn应用导入GRN模型
from grn.models import GRN

class PutAway(models.Model):
    warehouse = models.ForeignKey(Warehouse, on_delete=models.CASCADE)
    # 替换字符串引用为直接引用模型类
    grn = models.ForeignKey(GRN, on_delete=models.CASCADE)
    employee_assigned = models.ForeignKey(Employee, on_delete=models.CASCADE)
    # 其余字段保持不变
    putaway_id = models.IntegerField(default=0)
    products_position = models.ManyToManyField(PutAwayProductsPosition)
    completely_executed = models.BooleanField(default=False)
    partially_executed = models.BooleanField(default=False)
    created = models.DateTimeField(auto_now_add=True)
    scheduled_datetime = models.DateTimeField(auto_now_add=True)
    owner = models.ForeignKey(User, on_delete=models.CASCADE)

2. 清理重复迁移并重新同步 #

• 删除putpick和grn应用下最近生成的重复迁移文件（比如0034_xxx、0035_xxx、0069_xxx这类重复的AlterField迁移）
• 运行命令清理迁移缓存并标记现有迁移已应用：

  python manage.py migrate --fake-initial
  

• 重新生成迁移并应用：

  python manage.py makemigrations
  python manage.py migrate
  

3. 检查关联应用的迁移稳定性 #

查看grn应用的0069_auto_20230411_0828.py迁移文件，确认它修改的grntempscans模型的grn字段是否会影响GRN模型的schema状态。如果grn应用存在未完成的模型变更，先完成并稳定grn的迁移，再处理putpick的问题。

4. 重置迁移（仅开发环境使用） #

如果以上方法都无效，且处于开发环境（生产环境绝对禁止），可以重置迁移历史：

• 删除putpick和grn应用的migrations目录中除__init__.py外的所有文件
• 标记迁移历史为初始状态：

  python manage.py migrate --fake putpick zero
  python manage.py migrate --fake grn zero
  

• 重新生成并应用迁移：

  python manage.py makemigrations grn putpick
  python manage.py migrate
  

内容的提问来源于stack exchange，提问作者Rahul Sharma