Django 模型在保存循环中生成数百个文件

Question

我在 Ubuntu 18.04 上使用 Django 3.8.2，我在保存 Django 模型时生成了一个 PDF 文件，但是文件是无限循环生成的。

我有这个 django 模型：

class Fattura(models.Model):
   ordine = models.ForeignKey(Ordine, on_delete=models.CASCADE, related_name="fatture", null=False)
   pdf = models.FileField(upload_to='archivio/fatture/%Y/%m')

pdf 字段是在保存实例时根据相关“ordine”字段中包含的信息生成的，该字段是另一个模型的外键：

class Ordine(models.Model):

   utente = models.ForeignKey(User, on_delete=models.CASCADE, related_name="ordini", null=False)
   data = models.DateField(auto_now_add=True)
   abbonamento = models.ForeignKey(Abbonamento, on_delete=models.PROTECT, null=False)
   importo = models.DecimalField(max_digits = 5, decimal_places = 2, null=False)

我在 Fattura 模型的 save() 方法中声明了生成 PDF 的所有指令。我正在使用 Django 文档推荐的库：reportlab。这是自定义保存方法：

    def save(self, *args, **kwargs):

       self.count_save += 1 # I defined this attribute which I increment to understand what is actually looping
       print("COUNT SAVE: " + str(self.count_save)) # it always grows, that's the save method being re-called

       if self.pdf._file == None:

          try:
             buffer = io.BytesIO()

             p = canvas.Canvas(buffer)

             p.drawString(100,100, str(self.ordine))
             p.showPage()
             p.save()

             buffer.seek(0)

             utente = self.ordine.utente

             num_questa_fattura = utente.ordini.count()

             nome_file = "{}_{}-{}.pdf".format(
                self.ordine.utente.first_name.lower(),
                self.ordine.utente.last_name.lower(),
                num_questa_fattura)
            
             percorso = '{}/upload/archivio/fatture/{}/{}/{}'.format(
                BASE_DIR, # from settings.py
                self.ordine.data.year,
                self.ordine.data.month,
                nome_file)

             file_temporaneo = NamedTemporaryFile(delete=True)


             file_temporaneo.write(buffer.getbuffer())

             file_temporaneo.flush()

             temp_file = File(file_temporaneo, name = nome_file)

             print(nome_file)
             print(file_temporaneo)
             print("--------------------- SAVE")

             self.pdf.save(nome_file, file_temporaneo, save=True) # saving the field (EDIT: this was the problem, setting save to True resaves the whole model object, and it was creating an infinite loop)
             file_temporaneo.close()


           except:

             raise ValidationError("Invoice could not be saved")

       super().save(*args, **kwargs) # saving the object to the database

当我使用 Django 管理面板保存 Fattura 对象时，在我声明的文件夹内循环生成数百个 PDF 文件，但没有真正完成数据库保存。之后没有可用的 Django 模型对象，因此最终没有任何内容保存到数据库中，每次生成恰好 499 个文件。

我不确定是什么导致了这个循环，也许是 try 语句中的 pdf 字段保存方法？还是最后的super().save(*args, **kwargs)？不过我无法删除它，否则如果 PDF 文件实际上与一个实例关联并且我正在更新另一个字段，则不会保存任何内容 ordine

这是我的日志的摘录

[Tue Nov 02 15:25:06.974768 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] COUNT SAVE: 262
[Tue Nov 02 15:25:07.010584 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] maria_rosselli-1.pdf
[Tue Nov 02 15:25:07.015778 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] <tempfile._TemporaryFileWrapper object at 0x7f7b07ac0390>
[Tue Nov 02 15:25:07.020944 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] --------------------- SAVE
[Tue Nov 02 15:25:07.124451 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] COUNT SAVE: 263
[Tue Nov 02 15:25:07.164934 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] maria_rosselli-1.pdf
[Tue Nov 02 15:25:07.170144 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] <tempfile._TemporaryFileWrapper object at 0x7f7b07ac0e48>
[Tue Nov 02 15:25:07.175250 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] --------------------- SAVE
[Tue Nov 02 15:25:07.253426 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] COUNT SAVE: 264
[Tue Nov 02 15:25:07.286589 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] maria_rosselli-1.pdf
[Tue Nov 02 15:25:07.291734 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] <tempfile._TemporaryFileWrapper object at 0x7f7b07ac0e10>
[Tue Nov 02 15:25:07.296894 2021] [wsgi:error] [pid 10050] [remote 95.x.x.x:36048] --------------------- SAVE

Answer 1

保存pdf时需要设置save为False才能再次调用模型实例save方法：

self.pdf.save(nome_file, file_temporaneo, save=False)

Django 模型在保存循环中生成数百个文件

Django model generates hundreds of files in a saving loop

python-3.x

django

django-models

reportlab

temporary-files