如何解决django唯一约束的奇怪异常答案

【问题标题】：How to solve the strange exception of django unique constraint如何解决django唯一约束的奇怪异常
【发布时间】：2015-03-26 12:39:01
【问题描述】：

这就是我的 models.py 的样子：

class Project(models.Model):
    name = models.CharField(max_length="40", unique=True)

class Entry(models.Model):
    project = models.ForeignKey(Project)
    name = models.CharField(max_length="40",unique=False)

当我想创建一个新条目时我会使用 ajax 将条目的名称发布到服务器

createEntry 负责处理 ajax 发布请求

def createEntry(request):     
    if request.method == 'POST':   
        response_data = {}    
        name = request.POST.get('name')
        projectId = request.session['projectId'] 
        try:
            project = Project.objects.get(pk=projectId)
            entry=Entry(name=name)         
            project.entry_set.add(entry)   
        except:
            print traceback.format_exc()   
            return HttpResponseBadRequest("Failed")
    response_data['result'] = 'Create post successful!'

    return JsonResponse(response_data)

一切都很顺利，只是当创建一个与现有条目同名的新条目时会发生异常

这是回溯信息

Traceback (most recent call last):
  File "/home/vagrant/src/src/views.py", line 70, in createEntry
    project.entry_set.add(entry)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/related.py", line 708, in add
    obj.save()
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 589, in save
    force_update=force_update, update_fields=update_fields)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 617, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 698, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 731, in _do_insert
    using=using, raw=raw)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line 92, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 921, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py", line 920, in execute_sql
    cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 81, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/sqlite3/base.py", line 485, in execute
    return Database.Cursor.execute(self, query, params)
IntegrityError: UNIQUE constraint failed: src_entry.name

这是我的问题：

既然我已经用unique=False显式定义了Entry的name字段，那么name字段不应该有唯一性约束，那么这个异常怎么会发生呢？

【问题讨论】：

原来是unique=True，然后改了吗？如果是这样，您需要创建并运行迁移。
以前是独一无二的吗？更改后是否迁移了数据库？
我在将 unique 更改为 False 后运行了迁移，但它显示No changes detected。

标签： python django database unique

【解决方案1】：

数据库正在强制执行此 UNIQUE 约束。您将需要运行迁移以移除约束。

【讨论】：

【解决方案2】：

检查数据库迁移是否有任何问题。如果您使用的是 django 数据库内置的数据库 postgresql 或 sqlite 之一，您可以执行以下操作。

1.sqlite:- 只需删除 django 框架中的 sqlite 数据库容器并执行以下操作

$python manage.py makemigrations
$python manage.py migrate
$python manage.py runserver

2.postgresql :- 您需要通过以下步骤删除数据库

$sudo -u postgres psql
postgresql#drop database YOUR_DATABASE_NAME
postgresql#create database NEW_DATABASE_NAME
postgresql#grant all privileges on database "NEW_DATABASE_NAME" to YOUR_USER_NAME

$python manage.py makemigrations
$python manage.py migrate
$python manage.py createsuperuser
$python manage.py runserver

【讨论】：