MultipleObjectsReturned: get() returned more than one Embed

We are getting this quite a lot.

We have a Sentry report over here: https://beta.getsentry.com/share/group/34313638322e3833333433303131/

MultipleObjectsReturned: get() returned more than one Embed -- it returned 2!
  File "django/core/handlers/base.py", line 137, in get_response
    response = response.render()
  File "django/template/response.py", line 103, in render
    self.content = self.rendered_content
  File "django/template/response.py", line 80, in rendered_content
    content = template.render(context)
  File "django/template/base.py", line 148, in render
    return self._render(context)
  File "django/template/base.py", line 142, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 844, in render
    bit = self.render_node(node, context)
  File "django/template/base.py", line 858, in render_node
    return node.render(context)
  File "django/template/loader_tags.py", line 126, in render
    return compiled_parent._render(context)
  File "django/template/base.py", line 142, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 844, in render
    bit = self.render_node(node, context)
  File "django/template/base.py", line 858, in render_node
    return node.render(context)
  File "django/template/loader_tags.py", line 65, in render
    result = block.nodelist.render(context)
  File "django/template/base.py", line 844, in render
    bit = self.render_node(node, context)
  File "django/template/base.py", line 858, in render_node
    return node.render(context)
  File "django/template/base.py", line 904, in render
    return render_value_in_context(output, context)
  File "django/template/base.py", line 881, in render_value_in_context
    value = force_text(value)
  File "django/utils/encoding.py", line 83, in force_text
    s = six.text_type(s)
  File "wagtail/wagtailcore/blocks/stream_block.py", line 311, in __str__
    return self.stream_block.render(self)
  File "wagtail/wagtailcore/blocks/base.py", line 216, in render
    return self.render_basic(value)
  File "wagtail/wagtailcore/blocks/stream_block.py", line 201, in render_basic
    [(force_text(child), child.block_type) for child in value]
  File "wagtail/wagtailcore/blocks/stream_block.py", line 201, in <listcomp>
    [(force_text(child), child.block_type) for child in value]
  File "django/utils/encoding.py", line 83, in force_text
    s = six.text_type(s)
  File "wagtail/wagtailcore/blocks/stream_block.py", line 251, in __str__
    return self.block.render(self.value)
  File "wagtail/wagtailcore/blocks/base.py", line 216, in render
    return self.render_basic(value)
  File "wagtail/wagtailcore/blocks/base.py", line 223, in render_basic
    return force_text(value)
  File "django/utils/encoding.py", line 83, in force_text
    s = six.text_type(s)
  File "wagtail/wagtailembeds/blocks.py", line 21, in __str__
    return embed_to_frontend_html(self.url)
  File "wagtail/wagtailembeds/format.py", line 10, in embed_to_frontend_html
    embed = embeds.get_embed(url)
  File "wagtail/wagtailembeds/embeds.py", line 128, in get_embed
    return Embed.objects.get(url=url, max_width=max_width)
  File "django/db/models/manager.py", line 92, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "django/db/models/query.py", line 361, in get
    num if num <= MAX_GET_RESULTS else 'more than %s' % MAX_GET_RESULTS

[gasman]

I believe this is now fixed as of #6635 and #6815 - #6635 replaced the old unique_together constraint (with its unexpected treatment of null fields) with a unique constraint on the hash field (where that quirk doesn’t arise), and #6815 cleans up the duplicate records that were presumably created as a result of this bug.

[gasman]

@lee-kagiso Thanks!

@kaedroho Argh, yes, you’re right - have just confirmed that Postgres will let me insert multiple records for the same URL with a null max_width. As far as I’m aware, the race condition protection in get_or_create relies on the database enforcing this - very annoying. I guess the most sensible solution is to use something like -1 as a ‘magic number’ in place of null. (I suggest -1 rather than 0, as 0 might conceivably be a valid parameter - if you want an invisible audio embed, for example.)