Django 模型中的 OnetoMany 字段

Question

根据我的搜索，我了解到 django 中没有 OnetoMany 字段，如果我想让这三个类相互连接，有人可以解释或简化解决方案吗？

a UserRank class 我可以定义任意多的等级，例如（船长、二等工程师、大副等） a User class 可以具有上述等级之一，一个 job class 可以从 UserRank class

中有 1 个或多个等级

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

您可能正在寻找外键关系的“反向关系”。查看 Django 文档：Following relationships backwards

（总结：Entry 有一个指向 Blog 的外键，默认情况下 Blog.entry_set 是相关 Entry 对象的管理器，f.ex。 Blog.entry_set.all() 或任何更复杂的查询集来过滤它们。名称 entry_set 是默认名称，您可以通过 Entry 中 ForeignKey 上的 related_name 更改它）

Answer 2

在 one-to-many 关系中，“子”实例包含父实例的主键作为外键。

这意味着如果您在 UserRank 和 Job 之间建立关系，则每个 Job instance 将具有一个类型为 ForeignKey 的属性，其中包含父项的主键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

Django 模型中的 OnetoMany 字段

OnetoMany field in django models

django

django-models