Question

How to write joins in django,i have gone through below django documentation ,but joins are not working for my model

http://docs.djangoproject.com/en/1.2/topics/db/queries/#lookups-that-span-relationships

and models/many_to_many/

and some blogs

My Model :

class Profile(models.Model):
     name = models.CharField(max_length=50, primary_key=True)
     assign = models.CharField(max_length=50)
     doj = models.DateField()
     dob = models.DateField()

     class Meta:
        db_table = u'profile'

     def __str__(self):
         return  '%s %s %s %s' % ( self.name,self.assign,self.doj,self.dob)

     def __unicode__(self):
         return  u'%s %s %s %s' % ( self.name,self.assign,self.doj,self.dob)


     enter code here

class working(models.Model):
   w_name =models.ForeignKey(Profile, db_column='w_name')
   monday =  models.IntegerField(null=True, db_column='monday', blank=True)
   tuesday =  models.IntegerField(null=True, db_column='tuesday', blank=True)
   wednesday =  models.IntegerField(null=True, db_column='wednesday', blank=True)

   class Meta:
        db_table = u'working'

   def __str__(self):
         return  '%s %s %s %s' % ( self.w_name,self.monday,self.tuesday,self.wednesday)

   def __unicode__(self):
         return  u'%s %s %s %s' % ( self.w_name,self.monday,self.tuesday,self.wednesday)

I am trying to do join between two tables profile and workingday

like m=working.objects.filter(name='sushanth').select_related()

if i run above query i’ll get

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/lib/pymodules/python2.6/django/db/models/manager.py", line 129, in filter
    return self.get_query_set().filter(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/django/db/models/query.py", line 498, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/django/db/models/query.py", line 516, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/usr/lib/pymodules/python2.6/django/db/models/sql/query.py", line 1675, in add_q
    can_reuse=used_aliases)
  File "/usr/lib/pymodules/python2.6/django/db/models/sql/query.py", line 1569, in add_filter
    negate=negate, process_extras=process_extras)
  File "/usr/lib/pymodules/python2.6/django/db/models/sql/query.py", line 1737, in setup_joins
    "Choices are: %s" % (name, ", ".join(names)))
FieldError: Cannot resolve keyword 'name' into field. Choices are:  monday,  tuesday, wednesday,  w_name

I need to query where i can join working and profile.

support

select working.*,profile.assign,profile.doj from working join profile where name=w_name ;

I know django won’t support joins,inner join is also okay for me.

Can any one help on this…………………….?

Answer 1

Please format your question so that the code is readable (the {} icon) otherwise it is very hard to read.

working.objects.filter(name= will fail because your working model doesn’t have a name field.

From the docs you linked to:

Django offers a powerful and intuitive
way to “follow” relationships in
lookups, taking care of the SQL JOINs
for you automatically, behind the
scenes. To span a relationship, just
use the field name of related fields
across models, separated by double
underscores, until you get to the
field you want.

That translates to:

m = working.objects.filter(w_name__name='sushanth').select_related()