title: Restoring Django Model Field after accidental deletion
body: <p>I have an existing events model in my django app that lists events. The events has a poster field that was using the models.ImageField for storing the related poster. The uploading of events was controlled from the admin only so no public uploading. The database had about 50 entries of events and things were working fine.
  Since the images was getting heavier, I tried adding the sorl.thumnail to django. In my models.py file, I imported the ImageField from sorl.thumbnails and added it to the poster field. </p>
  
  <p>When I ran makemigrations, it reported 'alter field poster' Then I ran migrate and on reloading, I do not see the Poster field in the admin. 
  Even the existing events have lost the poster field and the images cannot be shown in the templates too. </p>
  
  <p>I have reverted the changes and run migrations again, but the poster field is still not visible. Is there any way to restore the model, and reconnect it with existing poster images?
  I am using python 3.5 and django 1.11 Everything else works fine, this seems like a stupid mistake for the sake of getting a little more speed. </p>
  
  <p>Will be grateful for any suggestions. </p>
  
  <p>Here is what my Events model looks like<code>class Events(models.Model):
      title = models.CharField(max_length=200)
      note = RichTextUploadingField()
      category = models.CharField(max_length=1, choices=EVENT_TYPES, verbose_name=_('Event Category'))
      date_from = models.DateTimeField(auto_now=False, blank=False)
      date_to = models.DateTimeField(auto_now=False, blank=False)
      poster = models.ImageField(upload_to='Programs/', blank=True, max_length=100, width_field=None, height_field=None)
      video = models.URLField(max_length=500, blank=True)
      capacity = models.SmallIntegerField(blank=True)
      venue = GeopositionField(blank=True)
  </code></p>
  
  <p>Admin.py is simply a register function</p>
  
  <pre><code>class EventAdmin(admin.ModelAdmin):
  list_display = ('title', 'date', 'venue', 'category')
  </code></pre>
  
  <p>admin.site.register(Event, EventAdmin)</p>