当已经有ID字段时，如何使UUID字段成为默认字段 [英] How to make UUID field default when there's already ID field

问题描述

我正在处理一个项目，问题是我已经用简单的ID列创建了模型，但是现在我的要求已更改，我想用UUID字段替换ID字段(模型)，我刚刚更新了模型:

I'm working on a project and problem is I've already created models with simple ID column but now my requirements are changed and I want to replace ID field (model) with UUID field I just updated my model:

uuid = models.UUIDField(primary_key=True, default=uuid.uuid4)

但是当我运行迁移时，我得到了一个错误

but when I run my migrations I got an error

django.db.utils.OperationalError :( 1829，无法删除列'id':外键约束中需要的

django.db.utils.OperationalError: (1829, "Cannot drop column 'id': needed in a foreign key constraint

请指导我如何执行此迁移?

Please guide me how can I perform this migration?

推荐答案

这是您需要执行的操作列表

here are the list of actions that you need to do

1-将新的 uuid 字段添加到模型中(我将此模型命名为 Base )，然后生成迁移文件

1 - add the new uuid field to model (I name this model Base) then generate migration files

uuid = models.UUIDField(默认= uuid4，空白=真，null =真)

uuid = models.UUIDField(default=uuid4, blank=True, null=True)

• 请注意，uuid还不是主键
• 请注意， blank = null = True

2-在此步骤中，应使用有效数据填充 uuid 字段.您应该为 Base 模型编写一个数据迁移文件.请查看文档以获取更多信息

2- in this step you should populate uuid field with valid data. you should write a data migration file for Base model. please check docs for more info

您的转发方法应如下所示:

your forwards method should be something like this:

for item in Base.objects.all():
    item.uuid = uuid4()
    item.save()

3-将此字段更改为uuid并生成迁移

3- change uuid field to this and generate migrations

uuid = models.UUIDField(默认= uuid4，唯一=真)

uuid = models.UUIDField(default=uuid4, unique=True)

• 请注意，uuid尚不是主键，但现在是唯一的

4-对于其他指向 Base 模型的模型，您应该添加一个指向uuid字段的新外键

4 - for other models which are pointing to Base model you should add a new foreignkey pointing to uuid field

假设您与基本模型的默认关系是这样的

assumig your default relation to Base model is something like this

base = models.ForeignKey(
    Base, on_delete=models.PROTECT, related_name='base'
)

您应该添加一个这样的临时字段

you should add a temprory field like this

base_uuid = models.ForeignKey(
    Base,
    on_delete=models.PROTECT,
    related_name='base_uuid',
    to_field='uuid',
    blank=True,
    null=True,
)

• 请注意，我已经明确定义了 to_field ，它告诉django这个外键没有指向默认的 pk 字段
• 您应该保留旧的外键字段
• 还设置 blank = null = True
• 对于所有指向 Base 的外键/manytomanyfield，您应添加此临时字段
• note that I have explicitly defined to_field which tell django this foreign key is not pointing to default pk field
• you should keep old foreign key field
• also set blank = null = True
• for all foreignkeys/manytomanyfield pointing to Base you should add this temp field

5-在此步骤中，您应该创建一个数据迁移文件，

5- in this step you should create a data migration file,

在此数据迁移文件中，您需要使用有效数据(基于旧的 base 字段)填充所有 base_uuid 字段，您的迁移代码可以是这样的

in this data migration file you need to fill all base_uuid fields with valid data (based on old base field) your migration code can be something like this

用于RelatedModel.objects.all()中的项目:item.base_uuid_id = item.base.uuid

• 此步骤之后，所有模型中的所有 base_uuid 字段均应包含有效数据
• after this step all base_uuid fields in all models should contain a valid data

6-在所有相关模型中删除相关字段(保留新的 base_uuid 字段，但丢弃旧的相关字段)并生成迁移文件

6- in all related models drop related field (keep the new base_uuid field but discard old related field) and generate a migration file

7-删除所有FK字段上的db_constraint-这是必需的，因为django将通过 base_uuid 的唯一约束进行连接，如果将 uuid 更改为PK.

7- delete the db_constraint on all FK fields - this is needed, because django will connect through the unique constraint from base_uuid which will be dropped if we change uuid to pk.

base_uuid = models.ForeignKey(
    Base,
    on_delete=models.PROTECT,
    related_name='base_uuid',
    to_field='uuid',
    blank=True,
    null=True,
    db_constraint=False
)

8-在 Base 模型中更改uuid字段并生成迁移文件

8- in Base model change uuid field and generate a migration file

uuid = models.UUIDField(默认= uuid4，primary_key = True)

uuid = models.UUIDField(default=uuid4, primary_key=True)

• uuid现在是主键！

9-在所有相关模型(已添加 base_uuid 字段的模型)中更新字段

9- in all related models (models which you have added base_uuid fields) update the field

• 重命名字段名称(从列名称中删除 _uuid )(将其设为单个迁移！)
• 更改 relate_name 字段名称(从相关名称中删除 _uuid )
• 如有必要，删除 blank = null = true
• 删除 to_field ='uuid'参数(不再需要此参数)
• rename field name (remove _uuid from column name) (make this a individual Migration!)
• change relate_name field name (remove _uuid from related name)
• remove blank = null = true if necessary
• remove to_field='uuid' argument (you don't need that any more)

非常重要的提示::在测试数据上运行这些代码并从数据库创建完整备份，然后再对实际数据运行此代码

Very Important Note: run these code with test data and create a full backup from your database before running this code on your actual data

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