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

Question

我正在尝试为我的数据库记录某机构中基于网络的课程规划应用程序。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 处的值错误

精确查找的 QuerySet 值必须使用切片限制为一个结果。

请求方法：POST 请求网址：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 值必须使用切片限制为一个结果。

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 

models.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)

views.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')

Answer 1

这行不通。

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)

在直通模型中创建一个AvoirCursus 实例。

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

我对其进行了测试，它至少在我的控制台中有效。

# 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)

这是我做的检查：

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)

这非常有效。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，则可以重建您的数据库。

Answer 2

我已经成功解决了我的问题。视图中使用的表单是 models.py 中的通用表单。当我打印（cursus）时，结果是一个包含所选项目的查询集。为了在中间数据库中写入，我制作了“cursus”的过程来拥有不同的对象。

views.py 是：

if f.is_valid():
            dept = f.save(commit=False)
            code_departement = f.cleaned_data['code_departement']
            dept.code_departement = code_departement
            print(code_departement)
            cursus = f.cleaned_data['cursus']
            dept.save()
            for i in cursus:
                AvoirCursus.objects.create(departement=dept, cursus=i)