Django不能添加或更新子行:外键约束失败

Question

好吧，之前问过的类似问题似乎对此没有一个有效的答案。我有一个Django应用程序，运行良好，但是现在在基于web的应用程序或命令行中使用这些模型，请告诉我上面的错误。我所有的表都是Innodb，我已经运行了syncdb。关闭完整性检查似乎有违直觉。如果我在这里或之前的答复中忽略了显而易见的内容，我很抱歉。任何帮助，谢天谢地。

来自models.py

class difficulty(models.Model):
    difficultyName = models.CharField(max_length=40)
    difficultyDescription = models.CharField(max_length=200)
    blank=False;
    def __unicode__(self):
        return self.difficultyName


class task(models.Model):
    question     = models.CharField(max_length=200)
    dateEntered  = models.DateTimeField('date entered') #, editable=False)
    difficulty   = models.ForeignKey(difficulty)
    taskClass    = models.ManyToManyField(taskClass,related_name ='taskClass')
    keyword      = models.ManyToManyField(keyword)
    service      = models.ManyToManyField(service)#, default = service.objects.get(serviceName='Medicine'))
    answer       = models.ManyToManyField(answer,  related_name = 'taskAnswer')
    def __unicode__(self):
        return "A task - {0}\n with difficulty {1}\n and date {2}\n".format(self.question, self.difficulty, self.dateEntered)

在views.py中，对象被实例化并保存如下

if form.is_valid():                         # All validation rules pass
    theNewTask = form.save(commit=False)
    theNewTask.dateEntered = timezone.now()
    theNewTask.save()      # the rest of the method deals with many-to-many relationships in the task class

它在通过基于模板的web表单处理时会产生以下错误：

异常值：(1452，“无法添加或更新子行:外键约束失败(djangoimp.twomt_task，constraint difficulty_id_refs_id_eca4bfb0 REFERENCES (difficulty_id) REFERENCES TwoMT_difficulty (id))”)

在python命令行中使用类：

>> import twomt.models as T
>> from django.utils import timezone
>> task = T.task(question="where is spain")
>> task.dateEntered = timezone.now()
>> task.difficulty = T.difficulty.objects.get(id=2)
>> task.save()

给出错误：

回溯(最近一次调用)：--狙击出跟踪-- IntegrityError：(1452，‘无法添加或更新子行:外键约束失败(djangoimp.twomt_task，constraint difficulty_id_refs_id_eca4bfb0 foreign key (difficulty_id) REFERENCES TwoMT_difficulty (id))“)

但是实例化的类很好：

>>> print task
A task - where is spain
 with difficulty Medium
 and date 2015-03-19 11:19:04.494322+00:00

>>> print  T.difficulty.objects.get(id=2)
Medium

显示来自TwoMT_task的列

Field           Type           Null   Key     Default   Extra
'question',     'varchar(200)','NO',  '' ,    NULL,     ''
'id',           'int(11)',     'NO',  'PRI',  NULL,     'auto_increment'
'difficulty_id','int(11)',     'NO',  'MUL',  NULL,      ''
'dateEntered',  'datetime',    'NO',  ' ',    NULL,      ''

显示来自twomt_difficulty的列

Field                  Type           Null   Key     Default   Extra
'id',                  'int(11)',     'NO',  'PRI',  NULL,     'auto_increment'
'difficultyName',      'varchar(40)', 'NO',   '',    NULL,     ''
'difficultyDescription','varchar(200)','NO',  '',    NULL,     ''

Answer 1

我也有同样的问题，用这个链接解决了：

https://logic.edchen.org/how-to-resolve-error-1452-23000-cannot-add-or-update-a-child-row-a-foreign-key-constraint-fails/

简历(从链接)：

生成错误1452 (23000)是因为引用表顺序的子列cid中的某些当前值不在被引用表客户的父列id中。在我们真正创建它之前，它已经违反了约束规则。因此，MySQL无法创建约束。

解决方案

所以现在，您必须识别违反约束的行并纠正它们。这工作辛苦吗？不怎么有意思。您可以使用以下语句标识行：

mysql> select * from orders where cid not in (select distinct id from customers);