亲爱的 StackOverflow 社区。 我的问题与将新记录插入到包含 many2many fields 字段的表有关。
我花了一整天的时间尝试自己解决这个问题，阅读 django 文档并在 stackoverflow 中冲浪。
我的模型.py:
from django.db import models
from django_extensions.db.models import TimeStampedModel
class clans(TimeStampedModel):
rfam_acc = models.CharField(max_length=7)
rfam_id = models.CharField(max_length=40)
description = models.CharField(max_length=100)
author = models.CharField(max_length=100)
comment = models.CharField(max_length=2000, null=True)
class Meta:
ordering = ('rfam_id',)
def __str__(self):
return self.rfam_id
class families(TimeStampedModel):
rfam_acc = models.CharField(max_length=7)
rfam_id = models.CharField(max_length=40)
description = models.CharField(max_length=75)
author = models.CharField(max_length=100)
clan = models.ManyToManyField(clans, null=True, blank=True)
comment = models.CharField(max_length=2000, null=True)
我的数据收集脚本(来自另一个数据库)和在我的数据库中的插入:(这是从 manage.py shell_plus 运行的)。
import mysql.connector
from browse.models import clans, families
def run():
#... Query from another DB
# Query for clans using cursor. assign results to list of lists row_clans
query_clans = ("SELECT c.clan_acc, c.id, c.description, c.author, c.comment FROM clan c")
cursor_clans.execute(query_clans)
row_clans = cursor_clans.fetchall()
# Creation of entry clans in the database.
for clan in row_clans:
clap = clans.objects.create(
rfam_acc=clan[0],
rfam_id=clan[1],
description=clan[2],
author=clan[3],
comment=clan[4],
)
# Query for families, that have clan = just created clan. Result in a list of lists row_family.
query_families = ("SELECT f.rfam_acc, f.rfam_id, f.description, f.author, f.comment, c.id FROM clan_membership cm, family f, clan c WHERE f.rfam_acc = cm.rfam_acc AND cm.clan_acc = c.clan_acc AND c.id =")
cursor_families.execute(query_families + "\"" + clan[1] + "\"")
row_family = cursor_families.fetchall()
# Creation of entryes families in the database.
for family in row_family:
families.objects.create(
rfam_acc=family[0],
rfam_id=family[1],
description=family[2],
author=family[3],
comment=family[4],
clan=clan[1]
)
print ("insert family ", family[1], " in ", clan[1])
# close the cursors and close the connection to the server
cursor_clans.close()
cursor_families.close()
cnx.close()
最后是 shell 中的错误:
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/Users/work/Desktop/StructuRNA/website/scripts/SQLfromRfamIntoClansFamily.py", line 42, in run
clan=clan[1]
File "/Users/work/Desktop/StructuRNA/.VirEnvStructuRna/lib/python3.6/site-packages/django/db/models/manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/Users/work/Desktop/StructuRNA/.VirEnvStructuRna/lib/python3.6/site-packages/django/db/models/query.py", line 397, in create
obj = self.model(**kwargs)
File "/Users/work/Desktop/StructuRNA/.VirEnvStructuRna/lib/python3.6/site-packages/django/db/models/base.py", line 550, in __init__
setattr(self, prop, kwargs[prop])
File "/Users/work/Desktop/StructuRNA/.VirEnvStructuRna/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 499, in __set__
manager = self.__get__(instance)
File "/Users/work/Desktop/StructuRNA/.VirEnvStructuRna/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 476, in __get__
return self.related_manager_cls(instance)
File "/Users/work/Desktop/StructuRNA/.VirEnvStructuRna/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 783, in __init__
(instance, self.source_field_name))
ValueError: "<families: families object>" needs to have a value for field "families" before this many-to-many relationship can be used.
有什么帮助吗？ 我不明白什么不起作用。
另一件有趣的事情是，在我的数据库中，我发现了第一个元素的插入(在我尝试运行脚本时重复了多次)。 该元素对于 m2m 字段也有其正确的值。
请您参考如下方法:
您需要先创建“家庭”对象的实例，然后才能向 ManyToManyField 添加条目
family = families.objects.create(
rfam_acc=family[0],
rfam_id=family[1],
description=family[2],
author=family[3],
comment=family[4]
)
family.clan.add(clan[1])
此外，您可能对 bulk_create 感兴趣:https://docs.djangoproject.com/en/1.10/ref/models/querysets/#bulk-create
