条件:Django==1.8.7 和 django-mptt==0.8.0。
有一个模型:
class Tree(mptt_models.MPTTModel):
name = models.CharField(max_length=120, unique=True)
slug = models.SlugField(max_length=256, unique=True)
parent = mptt_models.TreeForeignKey('self', null=True, blank=True,
related_name='children', db_index=True)
class MPTTMeta:
order_insertion_by = ['name']
我可以用管理界面填充它并显示在网站页面上。
我可以用 django shell 填充它:
Python 2.7.3 (default, Jun 22 2015, 19:43:34)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from src.catalog.models import Tree
>>> Tree.objects.create(name='1', slug='2')
<Tree: 1>
>>> Tree.objects.all()
[<Tree: 1>]
我编写了一个使用遗留模型中的信息填充树模型的迁移:
def propagate_tree(app_registry, schema_editor):
Category = app_registry.get_model('catalog', 'Category')
Tree = app_registry.get_model('catalog', 'Tree')
for category in Category.objects.all():
parent = Tree.objects.create(name=category.title, slug=category.slug)
for group in category.group_set.all():
Tree.objects.create(parent=parent, name=group.title, slug=group.slug)
我收到以下错误:
django.db.utils.IntegrityError: null value in column "lft" violates not-null constraint
执行该行时:
parent = Tree.objects.create(name=category.title, slug=category.slug)
仍然无法理解这个错误的原因:(