OnetoMany field in django models - django

Question

From my search it comes to my understanding there is no OnetoMany Field in django, can someone explain or simplify a solution if i wanted to have these three classes connected to each other.
a UserRank class which i can define as many as ranks i want,example (captain,2nd eng,chief mate...etc)
a User class which can have one of the above ranks,
a job class which can have 1 or many ranks from the UserRank class
models.py
class UserRank(models.Model):
rank = models.CharField(blank=True,null=True,max_length=150)
def __str__(self):
return self.rank
class User(AbstractBaseUser, PermissionsMixin):
email = models.EmailField(unique=True)
username = models.CharField(max_length=150,unique=True)
name = models.CharField(max_length=150,)
phone = models.CharField(max_length=50)
date_of_birth = models.DateField(blank=True, null=True)
picture = models.ImageField(blank=True, null=True, upload_to='users_imgs')
is_staff = models.BooleanField(default=False)
is_active = models.BooleanField(default=True)
date_joined = models.DateTimeField(default=timezone.now)
last_login = models.DateTimeField(null=True)
user_rank = models.ForeignKey(UserRank,related_name='userRank',null=True,on_delete=models.SET_NULL)
objects = UserManager()
USERNAME_FIELD = 'username'
REQUIRED_FIELDS = ['email','name']
def get_full_name(self):
return self.username
def get_short_name(self):
return self.username.split()[0]
class Job(models.Model):
job_type = (
('I', 'Interval'),
('O', 'One time'),
)
name = models.CharField(max_length=100)
description = models.CharField(max_length=100)
type = models.CharField(max_length=1, choices=job_type)
interval = models.IntegerField()
is_critical = models.BooleanField()
due_date = models.DateField()
user_rank = models.ManyToManyField(UserRank,related_name='ranks',blank=True)
component = models.ForeignKey(
Component, related_name='jobs', on_delete=models.CASCADE)
runninghours = models.ForeignKey(
RunningHours, related_name="RHjobs", on_delete=models.CASCADE)
def __str__(self):
return self.name

Answer 1

You are probably looking for the "reverse relation" of a ForeignKey relation. Look at the Django documentation: Following relationships backwards
(Summary: Entry has a foreign key to Blog, and by default Blog.entry_set is a manager for related Entry objects, f.ex. Blog.entry_set.all() or any more complex Queryset to filter them. THe name entry_set is a default, you can change it via related_name on the ForeignKey in Entry)

Answer 2

In a one-to-many relationship, the "child" instance contains the primary key of the parent instance as a foreign key.
This means that if you have a relationship between UserRank and Job, each Job instance will have an attribute of type ForeignKey containing the primary key of the parent Job instance.
# Setup
class UserRank(models.Model):
...attributes
class Job(models.Model):
user_rank = models.ForeignKey(UserRank, on_delete=models.CASCADE, related_name="jobs")
# Accessing jobs from UserRank
user_rank_1 = UserRank.objects.create(...)
# There is one UserRank instance with many child job instances, so we have to cycle through them
for job in user_rank_1.jobs.all():
print(job)
# Result
# >>> job1
# >>> job2
# >>> job3
# Accessing UserRank from a Job instance
job = Job.objects.get(id=1)
# Every job instance only has one parent UserRank, so it's sufficient to reference it directly with the dot notation
print(job.user_rank)
# Result
# >>> user_rank_1