id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 8036 select_related() yields unexpected results with certain combinations of *fields Tai Lee Malcolm Tredinnick "When passing certain combinations of fields (vs depth or no arguments) to `select_related()`, I get an unexpected model instance (should be `None`) for a `ForeignKey` field which has `null=True`. Given the following models: {{{ class Country(models.Model): created = turbia_models.DateTimeField(auto_now_add=True) modified = turbia_models.DateTimeField(auto_now=True) name = turbia_models.CharField(max_length=50, unique=True) abbreviation = turbia_models.CharField(max_length=10, unique=True) def __unicode__(self): return self.name class State(models.Model): created = turbia_models.DateTimeField(auto_now_add=True) modified = turbia_models.DateTimeField(auto_now=True) country = models.ForeignKey(Country) name = turbia_models.CharField(max_length=50) abbreviation = turbia_models.CharField(max_length=10) def __unicode__(self): return self.name class ClientStatus(models.Model): created = turbia_models.DateTimeField(auto_now_add=True) modified = turbia_models.DateTimeField(auto_now=True) name = turbia_models.CharField(max_length=50, unique=True) def __unicode__(self): return self.name class Client(models.Model): created = turbia_models.DateTimeField(auto_now_add=True) modified = turbia_models.DateTimeField(auto_now=True) code = turbia_models.CharField(max_length=5, unique=True) name = turbia_models.CharField(max_length=50, unique=True) street_address_1 = turbia_models.CharField(max_length=50, null=True) street_address_2 = turbia_models.CharField(max_length=50, blank=True, null=True) suburb = turbia_models.CharField(max_length=50, null=True, verbose_name='town / suburb') city = turbia_models.CharField(max_length=50, blank=True, null=True) state = models.ForeignKey(State, null=True) post_code = turbia_models.CharField(max_length=10, null=True) country = models.ForeignKey(Country, null=True) telephone = turbia_models.CharField(max_length=20, null=True) fax = turbia_models.CharField(max_length=20, blank=True, null=True) web_site = models.URLField(blank=True, null=True, verify_exists=False) status = models.ForeignKey(ClientStatus, null=True) def __unicode__(self): return self.name class JobStatus(models.Model): created = turbia_models.DateTimeField(auto_now_add=True) modified = turbia_models.DateTimeField(auto_now=True) name = turbia_models.CharField(max_length=50, unique=True) sequence = models.IntegerField(default=0) def __unicode__(self): return self.name class Job(models.Model): created = turbia_models.DateTimeField(auto_now_add=True) modified = turbia_models.DateTimeField(auto_now=True) client = models.ForeignKey(Client) status = models.ForeignKey(JobStatus, null=True) type = models.ForeignKey(JobType, null=True) name = turbia_models.CharField(max_length=50) description = turbia_models.TextField(blank=True, null=True) people = models.ManyToManyField(Person, blank=True) }}} The following results are correct when using `select_related()`: {{{ >>> j = Job.objects.filter(pk=1264).select_related()[0] >>> j.client >>> j.client.status >>> j.status >>> type(j.status) }}} But when using `select_related('client__state__country', 'client__status', 'status')` I get the following unexpected results: {{{ >>> j = Job.objects.filter(pk=1264).select_related('client__state__country', 'client__status', 'status')[0] >>> j.client >>> j.client.status >>> type(j.client.status) >>> j.status Traceback (most recent call last): File """", line 1, in ? File ""/Users/tailee/3030/thirty30/django/db/models/base.py"", line 243, in __repr__ return smart_str(u'<%s: %s>' % (self.__class__.__name__, unicode(self))) TypeError: coercing to Unicode: need string or buffer, datetime.datetime found >>> type(j.status) >>> j.status.pk >>> j.status.created 1 >>> j.status.modified datetime.datetime(2008, 7, 25, 16, 52, 5, 753919) >>> j.status.name datetime.datetime(2008, 7, 25, 16, 52, 5, 753919) >>> j.status.sequence u'active' }}} It looks like `j.status` has taken properties from `j.client.status`, and mixed them up (e.g. `j.status.sequence` is the same as `j.client.status.name` in the expected results, possibly as a result of incorrect SQL when passing fields that are more than one relation away and have `null=True` and/or multiple `ForeignKey` fields named `status` (in different models). If I don't pass `client__state__country` to `select_related`, it works. If I assign a state to the client in question, it works. I'm having trouble writing a test to reproduce this outside of the real-world models above. Here is the SQL for the non-functioning queryset: {{{ >>> str(Job.objects.filter(pk=1264).select_related('client__state__country', 'client__status', 'status').query) 'SELECT ""smooth_job"".""id"", ""smooth_job"".""created"", ""smooth_job"".""modified"", ""smooth_job"".""client_id"", ""smooth_job"".""status_id"", ""smooth_job"".""type_id"", ""smooth_job"".""name"", ""smooth_job"".""description"", ""smooth_client"".""id"", ""smooth_client"".""created"", ""smooth_client"".""modified"", ""smooth_client"".""code"", ""smooth_client"".""name"", ""smooth_client"".""street_address_1"", ""smooth_client"".""street_address_2"", ""smooth_client"".""suburb"", ""smooth_client"".""city"", ""smooth_client"".""state_id"", ""smooth_client"".""post_code"", ""smooth_client"".""country_id"", ""smooth_client"".""telephone"", ""smooth_client"".""fax"", ""smooth_client"".""web_site"", ""smooth_client"".""status_id"", ""smooth_state"".""id"", ""smooth_state"".""created"", ""smooth_state"".""modified"", ""smooth_state"".""country_id"", ""smooth_state"".""name"", ""smooth_state"".""abbreviation"", ""smooth_country"".""id"", ""smooth_country"".""created"", ""smooth_country"".""modified"", ""smooth_country"".""name"", ""smooth_country"".""abbreviation"", ""smooth_clientstatus"".""id"", ""smooth_clientstatus"".""created"", ""smooth_clientstatus"".""modified"", ""smooth_clientstatus"".""name"", ""smooth_jobstatus"".""id"", ""smooth_jobstatus"".""created"", ""smooth_jobstatus"".""modified"", ""smooth_jobstatus"".""name"", ""smooth_jobstatus"".""sequence"" FROM ""smooth_job"" INNER JOIN ""smooth_client"" ON (""smooth_job"".""client_id"" = ""smooth_client"".""id"") LEFT OUTER JOIN ""smooth_state"" ON (""smooth_client"".""state_id"" = ""smooth_state"".""id"") LEFT OUTER JOIN ""smooth_country"" ON (""smooth_state"".""country_id"" = ""smooth_country"".""id"") LEFT OUTER JOIN ""smooth_clientstatus"" ON (""smooth_client"".""status_id"" = ""smooth_clientstatus"".""id"") LEFT OUTER JOIN ""smooth_jobstatus"" ON (""smooth_job"".""status_id"" = ""smooth_jobstatus"".""id"") WHERE ""smooth_job"".""id"" = 1264 ORDER BY ""smooth_job"".""id"" DESC' }}} " closed Database layer (models, ORM) dev fixed select_related real.human@… Accepted 0 0 0 0 0 0