Hey everyone. Is there a way to get the latest ManyToMany related
model? My models.py looks like this:
class Conference(models.Model):
name = models.CharField(max_length=30, unique=True)
class Team(models.Model):
name = models.CharField(max_length=30, unique=True)
conferences = models.ManyToManyField('Conference',
related_name='teams', through='ConferenceMembership')
def _get_current_conference(self):
return self.conferences.latest()
conference = property(_get_current_conference)
class Player(models.Model):
name = models.CharField(max_length=15, unique=True)
teams = models.ManyToManyField('Team', related_name='players',
through='TeamMembership')
def _get_current_team(self):
return self.teams.latest()
team = property(_get_current_team)
class ConferenceMembership(models.Model):
conference = models.ForeignKey('Conference')
team = models.ForeignKey('Team')
date_joined = models.DateField(auto_now_add=True)
class Meta:
get_latest_by = 'date_joined'
class TeamMembership(models.Model):
team = models.ForeignKey('Team')
player = models.ForeignKey('Player')
date_joined = models.DateField(auto_now_add=True)
class Meta:
get_latest_by = 'date_joined'
This is important because Teams can change Conferences, and Players
can change Teams, but their stats while on those Teams/Conferences
have to remain under those Teams/Conferences.
When I try and create a Team in the Admin section, the following happy
error comes up:
Exception Type: TemplateSyntaxError
Exception Value: Caught an exception while rendering: latest()
requires either a field_name parameter or 'get_latest_by' in the model
So I think, "Oh, I need to move those 'get_latest_by' declarations
into the top-level classes". So I change my models to look like this:
class Conference(models.Model):
name = models.CharField(max_length=30, unique=True)
class Meta:
get_latest_by = 'date_joined'
class Team(models.Model):
name = models.CharField(max_length=30, unique=True)
conferences = models.ManyToManyField('Conference',
related_name='teams', through='ConferenceMembership')
class Meta:
get_latest_by = 'date_joined'
def _get_current_conference(self):
return self.conferences.latest()
conference = property(_get_current_conference)
class Player(models.Model):
name = models.CharField(max_length=15, unique=True)
teams = models.ManyToManyField('Team', related_name='players',
through='TeamMembership')
class Meta:
get_latest_by = 'date_joined'
def _get_current_team(self):
return self.teams.latest()
team = property(_get_current_team)
class ConferenceMembership(models.Model):
conference = models.ForeignKey('Conference')
team = models.ForeignKey('Team')
date_joined = models.DateField(auto_now_add=True)
class TeamMembership(models.Model):
team = models.ForeignKey('Team')
player = models.ForeignKey('Player')
date_joined = models.DateField(auto_now_add=True)
But when trying to add another team, I get a different error:
Exception Type: TemplateSyntaxError
Exception Value: Cannot resolve keyword 'date_joined' into field.
Choices are: _order, conferencemembership, conferences, name, teams
So I then try to access class attributes:
class Conference(models.Model):
name = models.CharField(max_length=30, unique=True)
class Meta:
get_latest_by = 'date_joined'
class Team(models.Model):
name = models.CharField(max_length=30, unique=True)
conferences = models.ManyToManyField('Conference',
related_name='teams', through='ConferenceMembership')
class Meta:
get_latest_by = 'conferencemembership.date_joined'
def _get_current_conference(self):
return self.conferences.latest()
conference = property(_get_current_conference)
class Player(models.Model):
name = models.CharField(max_length=15, unique=True)
teams = models.ManyToManyField('Team', related_name='players',
through='TeamMembership')
def _get_current_team(self):
return self.teams.latest()
team = property(_get_current_team)
class ConferenceMembership(models.Model):
conference = models.ForeignKey('Conference')
team = models.ForeignKey('Team')
date_joined = models.DateField(auto_now_add=True)
class TeamMembership(models.Model):
team = models.ForeignKey('Team')
player = models.ForeignKey('Player')
date_joined = models.DateField(auto_now_add=True)
But I still get an error:
Exception Type: TemplateSyntaxError
Exception Value: Caught an exception while rendering: (1054, "Unknown
column 'conferencemembership.date_joined' in 'order clause'")
So my problem is that Conferences and Teams don't have dates to order
by, but their relationships do (when a Team joined a Conference and
when a Player joined a Team). I don't understand how to order those
relationships to get the latest one. Am I using ManyToMany wrong? I
don't see how else I would do it.
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