新的迁移添加了一个简单的表，在迁移过程中出现错误“Cannot add foreign key constraint”（无法添加外键约束）。
下面是一个名为EventLog的现有模型：

class EventLog(models.Model):
    """
    The event log.
    """
    user = models.ForeignKey(User, blank=True, null=True)
    timestamp = models.DateTimeField(auto_now=True)
    text = models.TextField(blank=True, null=True)
    ip = models.CharField(max_length=15)
    metadata = JSONField(default={},blank=True)
    product = models.TextField(default=None,blank=True, null=True)
    type = models.ForeignKey(EventType)

    def __unicode__(self):
        return "[%-15s]-[%s] %s (%s)" % (self.type, self.timestamp, self.text, self.user)

    def highlite(self):
        if self.type.highlite:
            return self.type.highlitecss
        return False

下面是我尝试创建的新模型：

class EventLogDetail(models.Model):
    # NOTE: I've already tried switching 'EventLog' out for just EventLog.
    eventlog = models.ForeignKey('EventLog', related_name='details')
    order = models.IntegerField(default=0)
    line = models.CharField(max_length=500)

    class Meta:
        ordering = ['eventlog', 'order']

看起来很简单，对吧？所以我进行了迁移：
./manage.py makemigrations：

Migrations for 'accounts':
  accounts/migrations/0016_eventlogdetail.py
    - Create model EventLogDetail

到目前为止，一切顺利。然后，我迁移，像这样：
./manage.py migrate：

Operations to perform:
  Apply all migrations: accounts, admin, attention, auth, contenttypes, freedns, hosting, info, mail, sessions, sites, taggit, vserver
Running migrations:
  Applying accounts.0016_eventlogdetail...Traceback (most recent call last):
  File "./manage.py", line 10, in 
    execute_from_command_line(sys.argv)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 363, in execute_from_command_line
    utility.execute()
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 355, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 204, in handle
    fake_initial=fake_initial,
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 93, in __exit__
    self.execute(sql)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 120, in execute
    cursor.execute(sql, params)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 101, in execute
    return self.cursor.execute(query, args)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/MySQLdb/cursors.py", line 205, in execute
    self.errorhandler(self, exc, value)
  File "/home/the_user/code/the_project/local/lib/python2.7/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
django.db.utils.IntegrityError: (1215, 'Cannot add foreign key constraint')

这就是迁徙本身，这一切都是Python的荣耀：

# -*- coding: utf-8 -*-
# Generated by Django 1.11.4 on 2017-08-30 12:51
from __future__ import unicode_literals

from django.db import migrations, models
import django.db.models.deletion

class Migration(migrations.Migration):

    dependencies = [
        ('accounts', '0015_product_public'),
    ]

    operations = [
        migrations.CreateModel(
            name='EventLogDetail',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('order', models.IntegerField(default=0)),
                ('line', models.CharField(max_length=500)),
                ('eventlog', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='details', to='accounts.EventLog')),
            ],
            options={
                'ordering': ['eventlog', 'order'],
            },
        ),
    ]

我尝试过重命名新模型和其中的所有内容（事件related_name属性），以防我使用的变量名已经被一些机器所使用，但结果相同。
在网上搜索，我只找到了Django这个问题的一个例子（Django MySQL error when creating tables），但这没有帮助。没有迁移到auth，我也不明白为什么会有，因为我们最近既没有弄乱这部分，也没有升级任何包。
任何帮助深表感谢。