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django - Django 错误：必须使用切片将精确查找的 QuerySet 值限制为一个结果

问题描述

我正在尝试为我的机构中基于 Web 的课程规划应用程序的数据库记录。我担心的是由于views.py中的关系M2M而无法在中间表中进行记录，但它可以在shell中工作

/config/departement 处的 ValueError

精确查找的 QuerySet 值必须限制为使用切片的一个结果。

请求方法：POST 请求 URL： http: //127.0.0.1 :8000/config/departement Django 版本：2.1.7 异常类型：ValueError 异常值：

精确查找的 QuerySet 值必须限制为使用切片的一个结果。

异常位置：C:\Program Files\Python37\lib\site-packages\django\db\models\lookups.py 在 process_rhs，第 257 行 Python 可执行文件：C:\Program Files\Python37\python.exe Python 版本：3.7。 0 Python 路径：

Traceback 切换到复制和粘贴视图

C:\Program Files\Python37\lib\site-packages\django\core\handlers\exception.py in inner

                response = get_response(request)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\core\handlers\base.py in _get_response

                    response = self.process_exception_by_middleware(e, request)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\core\handlers\base.py in _get_response

                    response = wrapped_callback(request, *callback_args, **callback_kwargs)

     ...
▶ Local vars
E:\PLACORESA\configuration\views.py in departemnent

                cursus = get_object_or_404(Cursus, libelle_cursus=cursus )

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\shortcuts.py in get_object_or_404

            return queryset.get(*args, **kwargs)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\query.py in get

            num = len(clone)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\query.py in __len__

            self._fetch_all()

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\query.py in _fetch_all

                self._result_cache = list(self._iterable_class(self))

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\query.py in __iter__

            results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\sql\compiler.py in execute_sql

                sql, params = self.as_sql()

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\sql\compiler.py in as_sql

                    where, w_params = self.compile(self.where) if self.where is not None else ("", [])

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\sql\compiler.py in compile

                sql, params = node.as_sql(self, self.connection)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\sql\where.py in as_sql

                    sql, params = compiler.compile(child)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\sql\compiler.py in compile

                sql, params = node.as_sql(self, self.connection)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\lookups.py in as_sql

            rhs_sql, rhs_params = self.process_rhs(compiler, connection)

     ...
▶ Local vars
C:\Program Files\Python37\lib\site-packages\django\db\models\lookups.py in process_rhs

                        'The QuerySet value for an exact lookup must be limited to '

     ...
▶ Local vars

模型.py

class Departement(models.Model):
    code_departement=models.CharField("code du département", max_length=100, unique=True)
    libelle_departement=models.CharField("Libellé du département", max_length=100)
    faculte=models.ForeignKey("Faculte", on_delete=models.CASCADE)
    cursus=models.ManyToManyField("Cursus", through="AvoirCursus")   



class Cursus(models.Model):
    code_cursus=models.CharField("Code du cursus", max_length=10, unique=True)
    libelle_cursus=models.CharField("Libellé du cursus", max_length=100) 

class AvoirCursus(models.Model):
    cursus=models.ForeignKey("Cursus", on_delete=models.CASCADE)
    departement=models.ForeignKey("Departement", on_delete=models.CASCADE)

视图.py

if request.method == 'POST':
        f = forms.Departement_Form(request.POST)
        if f.is_valid():
            dept = f.save(commit=False)
            code_departement = f.cleaned_data['code_departement'].upper()
            dept.code_departement = code_departement
            cursus = f.cleaned_data['cursus']
            dept.save()
            cursus = get_object_or_404(Cursus, libelle_cursus=cursus )
            print(cursus)
            AvoirCursus.objects.create(departement=dept, cursus=cursus)

            return redirect('configuration:lister_departement')

标签： django

解决方案

这是行不通的。

if request.method == 'POST':
            (...)
            dept=models.Departement.objects.get(code_departement=code_departement)
            cursus=models.Cursus.objects.get(code_cursus=cursus)
            avoircursus=models.AvoirCursus.objects.create(cursus=cursus, departemnent=dept)

我删除了models

if request.method == 'POST':
     (...)
     dept = Departement.objects.get(code_departement=code_departement)
     cursus = Cursus.objects.get(code_cursus=cursus)

创建一个AvoirCursus贯穿模型的实例。

AvoirCursus.objects.create((cursus=cursus, departemnent=dept)

我对其进行了测试，并且至少在我的控制台中可以正常工作。

# your models
class Faculte(models.Model):
    name = models.CharField("Libellé du département", max_length=100

class Departement(models.Model):
    code_departement = models.CharField("code du département", max_length=100, unique=True)
    libelle_departement = models.CharField("Libellé du département", max_length=100)
    faculte = models.ForeignKey("Faculte", on_delete=models.CASCADE)
    cursus = models.ManyToManyField("Cursus", through="AvoirCursus")

class Cursus(models.Model):
    code_cursus = models.CharField("Code du cursus", max_length=10, unique=True)
    libelle_cursus = models.CharField("Libellé du cursus", max_length=100)

class AvoirCursus(models.Model):
    cursus = models.ForeignKey("Cursus", on_delete=models.CASCADE)
    departement = models.ForeignKey("Departement", on_delete=models.CASCADE)

这是我为检查它所做的：

f = Faculte.objects.create(name='Sorbonne')
c = Cursus.objects.create(code_cursus='404')
d = Departement.objects.create(code_departement='code', libelle_departement='libelle', faculte=f)
ac = AvoirCursus.objects.create(cursus=c, departement=d)

这完美地工作。所以你的观点一定有问题。或者，如果您进行了未反映的更改，则可能重建您的数据库。

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