python - Django 从字符字段迁移到整数字段？

Question

我在models.py 中更改了我的CharField 之一:

models.CharField(max_length=128, blank=True)

进入 IntegerField -->

models.IntegerField(default=0)

我有该字段的数据，主要是空字符串( "" )或整数作为字符串(例如: "10" )。

所以我想在迁移时将这些字符串转换为整数。例如::
如果空白字符串( "" ) 转换为 0 , 否则转换为整数。

我怎样才能做到这一点，而我这样做 ./manage.py migrate命令？

这是使用 ./manage.py makemigrations 创建的迁移文件::

# Generated by Django 2.1.2 on 2018-10-25 04:57

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('dashboard', '0002_auto_20181024_1544'),
    ]

    operations = [
        migrations.AlterField(
            model_name='aclpermissions',
            name='ordering',
            field=models.IntegerField(default=0),
        ),
        migrations.AlterField(
            model_name='submenus',
            name='ordering',
            field=models.IntegerField(default=0),
        ),
        migrations.AlterField(
            model_name='subsubmenus',
            name='ordering',
            field=models.IntegerField(default=0),
        ),
    ]

当我运行时 ./manage.py migrate我有错误::

psycopg2.DataError: invalid input syntax for integer: ""

因为有空字符串的字段 "" .

所以我想将空字符串( "" )转换为 0 .

Answer 1

对于遇到此问题的其他人，您可以添加一个在其他迁移操作之前运行的函数:

class Migration(migrations.Migration):

    def blank_to_zero(apps, schema_editor):
        AclPermissions = apps.get_model('dashboard', 'AclPermissions')
        SubMenus = apps.get_model('dashboard', 'SubMenus')
        SubSubMenus = apps.get_model('dashboard', 'SubSubMenus')

        for obj in AclPermissions.objects.filter(ordering=''):
            obj.ordering = 0
            obj.save()

        for obj in SubMenus.objects.filter(ordering=''):
            obj.ordering = 0
            obj.save()

        for obj in SubSubMenus.objects.filter(ordering=''):
            obj.ordering = 0
            obj.save()

    dependencies = [
        ('dashboard', '0002_auto_20181024_1544'),
    ]

    operations = [
        migrations.RunPython(blank_to_zero),

        migrations.AlterField(... 
        # the rest of your operations
    ]

见 https://docs.djangoproject.com/en/dev/topics/migrations/#data-migrations有关编辑数据迁移的信息。