title: How to send signals in django after import data into model
body: <p>I am going to send signal to delete all cached after model is updated.</p>
  <p>My code work good if I add case by case. It doesnt work when I import file</p>
  <p>my model:</p>
  <pre><code>class testimport(models.Model):
      id=models.AutoField(primary_key=True)
      so_hd=models.CharField( max_length=50, unique=True)
      ten_kh=models.CharField( max_length=500)
      created_at=models.DateTimeField(auto_now_add=True)
      
  # pre_save method
  def pre_save_signal_import_redis(sender, instance, created,*args,  **kwargs):
      print(instance.so_hd)
      print(&quot;pre_save_signal_import&quot;)
      cache.delete(&quot;*&quot;)
  
  pre_save.connect(pre_save_signal_import_redis,sender=testimport)       
  </code></pre>
  <p>There is no error, It just doesnt print anything even data is updated
  If I add case by case, pre_save_signal_import_redis work good and print all
  my view to import code</p>
  <pre><code>if request.method == 'POST':
          myfile = request.FILES['myfile']             
          empexceldata = pd.read_excel(myfile, engine='openpyxl')
                          
          dbframe = empexceldata
          df_records = dbframe.to_dict('records')
          batch_size = 1000
          batch = []
          for record in df_records:
              model_instances = testimport(
              so_hd=record['SỐ HD'],
              ten_kh=record[&quot;TÊN KH&quot;],
  
          )
          batch.append(model_instances)
          testimport.objects.bulk_create(batch,batch_size)
  </code></pre>
  <p>Thanks for reading</p>