Strange behaviour when deleting object with generic relation

Hi,
I get a SQL error when deleting an object with a somewhat
complex
generic relation (the relation is to a model with a foreign
key to the
model with the GenericForeignKey).
The simplified structure is:

class Tag(models.Model):
   ...

class TaggedObject(models.Model):
   content_type = ...
   object_id = models.PositiveIntegerField("Object
ID")
   tag = models.ForeignKey(Tag)

   content_object = models.GenericForeignKey()

class UserTaggedObject(models.Model):
   user = ...
   object_tag = models.ForeignKey(TaggedObject)

class ArticleAttachment(models.Model):
   ...
   tags = models.GenericRelation(TaggedObject)
   user_tags = models.GenericRelation(UserTaggedObject)

then, when I delete an ArticleAttachment with delete(), I
get an
OperationalError exception, with (1054, "Unknown column
'object_id' in
'where clause'"). Drilling down through the backtrace,
the offending
SQL code is in:

django_src/django/db/backends/util.py in execute

  12. return self.cursor.execute(sql, params) ...

Local vars
Variable 	Value

params  (5L,)
self        <django.db.backends.util.CursorDebugWrapper
object at 0xb6cdda0c>
sql         'DELETE FROM `tags_usertaggedobject` WHERE
`object_id` IN (%s)'

which seems wrong to me, because "object_id" is in
tags_taggedobject
and not tags_usertaggedobject:

mysql> describe tags_taggedobject;
+-----------------+------------------+------+-----+---------
+----------------+
| Field           | Type             | Null | Key | Default
| Extra          |
+-----------------+------------------+------+-----+---------
+----------------+
| id              | int(11)          |      | PRI | NULL   
| auto_increment |
| content_type_id | int(11)          |      | MUL | 0      
|                |
| object_id       | int(10) unsigned |      |     | 0      
|                |
| tag_id          | int(11)          |      | MUL | 0      
|                |
+-----------------+------------------+------+-----+---------
+----------------+

mysql> describe tags_usertaggedobject;
+---------------+---------+------+-----+---------+----------
------+
| Field         | Type    | Null | Key | Default | Extra    
     |
+---------------+---------+------+-----+---------+----------
------+
| id            | int(11) |      | PRI | NULL    |
auto_increment |
| user_id       | int(11) |      | MUL | 0       |          
     |
| object_tag_id | int(11) |      | MUL | 0       |          
     |
+---------------+---------+------+-----+---------+----------
------+

Is this an error on my part? What am I doing wrong?
Thank you in advance.

Ciao,
Marco

-- 
Marco Pantaleoni

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Hi,
doesn't someone have any idea about this?
I'd really appreciate any help or suggestion.

Thanks!
Cheers,
Marco

Marco Pantaleoni wrote:
> Hi,
> I get a SQL error when deleting an object with a
somewhat complex
> generic relation (the relation is to a model with a
foreign key to the
> model with the GenericForeignKey).
> The simplified structure is:
>
> class Tag(models.Model):
>    ...
>
> class TaggedObject(models.Model):
>    content_type = ...
>    object_id = models.PositiveIntegerField("Object
ID")
>    tag = models.ForeignKey(Tag)
>
>    content_object = models.GenericForeignKey()
>
> class UserTaggedObject(models.Model):
>    user = ...
>    object_tag = models.ForeignKey(TaggedObject)
>
> class ArticleAttachment(models.Model):
>    ...
>    tags = models.GenericRelation(TaggedObject)
>    user_tags = models.GenericRelation(UserTaggedObject)
>
> then, when I delete an ArticleAttachment with delete(),
I get an
> OperationalError exception, with (1054, "Unknown
column 'object_id' in
> 'where clause'"). Drilling down through the
backtrace, the offending
> SQL code is in:
>
> django_src/django/db/backends/util.py in execute
>
>   12. return self.cursor.execute(sql, params) ...
>
> Local vars
> Variable 	Value
>
> params  (5L,)
> self       
<django.db.backends.util.CursorDebugWrapper object at
0xb6cdda0c>
> sql         'DELETE FROM `tags_usertaggedobject` WHERE
`object_id` IN (%s)'
>
> which seems wrong to me, because "object_id"
is in tags_taggedobject
> and not tags_usertaggedobject:
>
> mysql> describe tags_taggedobject;
>
+-----------------+------------------+------+-----+---------
+----------------+
> | Field           | Type             | Null | Key |
Default | Extra          |
>
+-----------------+------------------+------+-----+---------
+----------------+
> | id              | int(11)          |      | PRI |
NULL    | auto_increment |
> | content_type_id | int(11)          |      | MUL | 0  
    |                |
> | object_id       | int(10) unsigned |      |     | 0  
    |                |
> | tag_id          | int(11)          |      | MUL | 0  
    |                |
>
+-----------------+------------------+------+-----+---------
+----------------+
>
> mysql> describe tags_usertaggedobject;
>
+---------------+---------+------+-----+---------+----------
------+
> | Field         | Type    | Null | Key | Default |
Extra          |
>
+---------------+---------+------+-----+---------+----------
------+
> | id            | int(11) |      | PRI | NULL    |
auto_increment |
> | user_id       | int(11) |      | MUL | 0       |     
          |
> | object_tag_id | int(11) |      | MUL | 0       |     
          |
>
+---------------+---------+------+-----+---------+----------
------+
>
> Is this an error on my part? What am I doing wrong?
> Thank you in advance.
> 
> Ciao,
> Marco
> 
> -- 
> Marco Pantaleoni


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Hi panta,

panta schrieb:
>> I get a SQL error when deleting an object with a
somewhat complex
>> generic relation (the relation is to a model with a
foreign key to the
>> model with the GenericForeignKey).
>> The simplified structure is:
>>
>> class Tag(models.Model):
>>    ...
>>
>> class TaggedObject(models.Model):
>>    content_type = ...
>>    object_id =
models.PositiveIntegerField("Object ID")
>>    tag = models.ForeignKey(Tag)
>>
>>    content_object = models.GenericForeignKey()
>>
>> class UserTaggedObject(models.Model):
>>    user = ...
>>    object_tag = models.ForeignKey(TaggedObject)
>>
>> class ArticleAttachment(models.Model):
>>    ...
>>    tags = models.GenericRelation(TaggedObject)
>>    user_tags =
models.GenericRelation(UserTaggedObject)

I assume that in ArticleAttachment, tags is somehow
different 
from the tags you get via user_tags. (If it is the same,
then 
it's probably better to remove tags and join via user_tags).

Yeah, Django's ORM does have some problems when the same
table 
(the one for TaggedObject) is joined multiple times, be it 
directly or indirectly. I don't have any experience with 
GenericRelations, but I guess it's a bug in Django. Would
you 
please file a ticket for this so that it doesn't get lost?
Sorry, 
but I have no idea for a good work-around.

Michael

-- 
noris network AG - Deutschherrnstraße 15-19 - D-90429
Nürnberg -
Tel +49-911-9352-0 - Fax +49-911-9352-100

http://www.noris.de - The
IT-Outsourcing Company

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Michael Radziej wrote:
> Hi panta,
>
> >>
> >> class ArticleAttachment(models.Model):
> >>    ...
> >>    tags = models.GenericRelation(TaggedObject)
> >>    user_tags =
models.GenericRelation(UserTaggedObject)
>
> I assume that in ArticleAttachment, tags is somehow
different
> from the tags you get via user_tags. (If it is the
same, then
> it's probably better to remove tags and join via
user_tags).

yes, user_tags are tags "owned" by specific users,
while tags are set
by the editors and have no "owner".

>
> Yeah, Django's ORM does have some problems when the
same table
> (the one for TaggedObject) is joined multiple times, be
it
> directly or indirectly. I don't have any experience
with
> GenericRelations, but I guess it's a bug in Django.
Would you
> please file a ticket for this so that it doesn't get
lost? Sorry,
> but I have no idea for a good work-around.
>
> Michael

Ok, understood. I'll try to work-around this by replicating
TaggedObject fields in UserTaggedObject,
thus avoiding the indirection to the same table. This should
eliminate
the multiple (indirect) join.
I'll also file a ticket, following your suggestion.

Thank you for your help.
Ciao,
Marco


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