How to create multiple inner joins using Django ORM? - django

Question

I'm struggling to find documentation and examples to solve the following dilemma. I have two tables, Results (which contain results of a race) and Photos (where each photo contain runners in that race). Both tables contain entrant_numbers, i.e. the number of the runner in the race and the number of the runner in the photo. In SQL I joined them like so to get the total number of photo captures per runner.
SELECT * FROM Photo p
INNER JOIN Result r ON p.entrant_number=r.entrant_number AND p.race_year=r.race_year
WHERE r.user_id=123
My models are structured like so;
class Photo(models.Model):
photo_id = models.AutoField(primary_key=True)
race_id = models.ForeignKey('Race')
url_pre_string = models.CharField("URL pre-string", max_length=255)
filename = models.CharField("Filename", max_length=100)
extension = models.CharField("File extensions", max_length=4)
date_created = models.DateTimeField(auto_now_add=True)
date_updated = models.DateTimeField(auto_now=True)
class Race(models.Model):
race_id = models.AutoField(primary_key=True)
race_year = models.PositiveIntegerField("Race year", null=False, blank=False)
date_created = models.DateTimeField(auto_now_add=True)
date_updated = models.DateTimeField(auto_now=True)
class Result(models.Model):
result_id = models.AutoField(primary_key=True)
race_id = models.ForeignKey('Race')
position = models.PositiveIntegerField("Position", default=0)
entrant_number = models.PositiveIntegerField("Entrant number", default=0, null=True, blank=True)
user_id = models.ForeignKey(User, null=True)
date_created = models.DateTimeField(auto_now_add=True)
date_updated = models.DateTimeField(auto_now=True)
The most recent query I tried was;
photo_captures = Photo.objects.filter(result__user_id_id=current_user.id)
I was hoping this would traverse back through result and filter on the current user id.

Answer 1

You can join two tables by performing a raw SQL query.
You can check how to do this here
from django.db import connection
def my_custom_sql(self):
cursor = connection.cursor()
cursor.execute("select *
from myapp_photo p
inner join myapp_result r ON
p.entrant_number=r.entrant_number AND
p.race_year=r.race_year
WHERE r.user_id=123")
row = cursor.fetchone()
return row
Alternate way:
You can set foreign key in Photo model to Result model, following this you will have unique photos of the different results. Something like this :
class Result(models.Model):
results_id = models.AutoField(primary_key=True)
position = models.PositiveIntegerField("Position", default=0)
entrant_number = models.PositiveIntegerField("Entrant number", default=0, null=True, blank=True)
race_year = models.PositiveIntegerField("Race year", default=0)
user_id = models.ForeignKey(User, null=True)
date_created = models.DateTimeField(auto_now_add=True)
date_updated = models.DateTimeField(auto_now=True)
class Photo(models.Model):
result= models.ForeignKey(Result)
photo_id = models.AutoField(primary_key=True)
url_pre_string = models.CharField("URL pre-string", max_length=255)
filename = models.CharField("Filename", max_length=100)
extension = models.CharField("File extensions", max_length=4)
entrant_number = models.PositiveIntegerField("Entrant number", default=0, null=True, blank=True)
race_year = models.PositiveIntegerField("Race year", default=0)
date_created = models.DateTimeField(auto_now_add=True)
date_updated = models.DateTimeField(auto_now=True)
and then to fetch the photos for a particular result of year for a single user you can do
photos = Photo.objects.filter(entrant_number = result__entrant_number,
race_year = result__race_year,
result__user_id = 123)
ofcourse i haven't tested this but this should do the trick. let me know if this works or if you need any help.