Django : Get specific columns from multiple tables

Question

I need to fetch columns from multiple tables, how do I achieve this?

UserLog


+------------+----------+------+-----+---------+----------------+
| Field      | Type     | Null | Key | Default | Extra          |
+------------+----------+------+-----+---------+----------------+
| log_id     | int(11)  | NO   | PRI | NULL    | auto_increment |
| time       | datetime | NO   |     | NULL    |                |
| ip_address | char(15) | YES  |     | NULL    |                |
| event_id   | int(11)  | NO   | MUL | NULL    |                |
| user_id    | int(11)  | NO   | MUL | NULL    |                |
+------------+----------+------+-----+---------+----------------+

Events


+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| event_id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| description | varchar(200) | NO   |     | NULL    |                |
+-------------+--------------+------+-----+---------+----------------+

This is my models.py

class Events(models.Model):
        event_id = models.AutoField(primary_key=True,verbose_name="Event id")
        description = models.CharField(max_length=200,verbose_name="Description")

        def __unicode__(self):
                return u"%d : %s" % (self.event_id, self.description)

class UserLog(models.Model):
        log_id = models.AutoField(primary_key = True)
        user = models.ForeignKey(User)
        event = models.ForeignKey(Events,verbose_name = "event")
        time = models.DateTimeField(default=datetime.now,blank=True)
        ip_address = models.IPAddressField(null=True)


        def __unicode__(self):
                return u"%s (%s): %s" % (self.log_id, self.user, self.event)

Spcifically I want to do SELECT log_id,time,user_id,event_id,description from UserLog,Events where UserLog.event_id = Events.event_id

I tried UserLog.objects.filter(event_id__event_id).values('log_id','time','user_id','event_id','description') . But it says no such fields.

Is there something I need to change in my models class?

Answer 1

Try this:

UserLog.objects.filter(event_id=1).values('log_id', 
                                          'time',
                                          'user_id',
                                          'event_id', 
                                          'event__description')

Alternately, you could use select_related:

UserLog.objects.filter(event__id=1).select_related('event')

then you'll get UserLog objects, with the event pre-fetched, so you can access the event without triggering another query.

(Also, standard naming convention would be to call the model Event, not Events)

Answer 2

use select_related() like this:

UserLog.objects.filter(event_id__event_id=1).select_related('event').values('log_id','time','user_id','event_id', 'event__description')