Django model - how to define foreign key refer to another table? - django

Question

I'm working with a legay database so I have to set managed = False, which means I cannot update the database schema.
What I'm trying to do is select branches based on project id. Ideally in branches table it should have a project_id as foreign key but the previous system design is another table (branches_projects) stores this relationship.
I have been able to get around some problems using https://docs.djangoproject.com/en/1.11/topics/db/sql/#django.db.models.Manager.raw. raw() would return an RawQuerySet, which is not ideal.
I wonder if there's a way for me to define a foreign key in my branches table, which is the project_id, but refer/link that to the branches_projects table?
class Branches(models.Model):
name = models.CharField(max_length=128)
branchpoint_str = models.CharField(max_length=255)
dev_lead_id = models.IntegerField(blank=True, null=True)
source = models.CharField(max_length=255)
state = models.CharField(max_length=255)
kind = models.CharField(max_length=255)
desc = models.TextField(blank=True, null=True)
approved = models.IntegerField()
for_customer = models.IntegerField()
deactivated_at = models.DateTimeField(blank=True, null=True)
created_at = models.DateTimeField(blank=True, null=True)
updated_at = models.DateTimeField(blank=True, null=True)
codb_id = models.IntegerField(blank=True, null=True)
pm_lead_id = models.IntegerField(blank=True, null=True)
version = models.CharField(max_length=20, blank=True, null=True)
path_id = models.IntegerField(blank=True, null=True)
branchpoint_type = models.CharField(max_length=255, blank=True, null=True)
branchpoint_id = models.IntegerField(blank=True, null=True)
class Meta:
managed = False
db_table = 'branches'
verbose_name_plural = 'Branches'
class Projects(models.Model):
id = models.AutoField(primary_key=True)
name = models.CharField(max_length=40, primary_key=True)
status = models.CharField(max_length=255)
platform = models.CharField(max_length=255)
enabled = models.IntegerField()
path = models.CharField(max_length=128, blank=True, null=True)
tag_prefix = models.CharField(max_length=64, blank=True, null=True)
created_at = models.DateTimeField(blank=True, null=True)
updated_at = models.DateTimeField(blank=True, null=True)
codb_id = models.IntegerField(blank=True, null=True)
template = models.CharField(max_length=64, blank=True, null=True)
image_path = models.CharField(max_length=128, blank=True, null=True)
repository_id = models.IntegerField(blank=True, null=True)
number_scheme = models.CharField(max_length=32)
special_dir = models.CharField(max_length=32, blank=True, null=True)
project_family_id = models.IntegerField()
class Meta:
managed = False
db_table = 'projects'
verbose_name_plural = 'projects'
class BranchesProjects(models.Model):
# project_id = models.IntegerField()
# branch_id = models.IntegerField()
project = models.ForeignKey(Projects, on_delete=models.CASCADE)
branch = models.ForeignKey(Branches, on_delete=models.CASCADE)
class Meta:
managed = False
db_table = 'branches_projects'
My current raw query is like this
SELECT br.id, br.name, br.created_at, br.updated_at,
br.branchpoint_str, br.source
FROM branches as br
LEFT JOIN branches_projects as bp
ON br.id = bp.branch_id
WHERE bp.project_id = %s AND source != 'other'
ORDER BY updated_at DESC

Answer 1

I've finally got it working......
In the model, I use the manytomany as following:
class Branches(models.Model):
name = models.CharField(max_length=128)
project = models.ManyToManyField(Projects,
through='BranchesProjects',
related_name='project')
branchpoint_str = models.CharField(max_length=255)
Then to get the same result as my raw sql, i do the following:
def get_sb(project_id):
result = Branches.objects.filter(
project=Projects.objects.get(id=project_id).id,
).exclude(source='other').order_by('-updated_at')
print result.query
return result