Django模型：使用多个值作为键？

Posted 2023-02-24

【中文标题】Django模型：使用多个值作为键？

【英文标题】：Django models: Use multiple values as a key?

【发布时间】：2011-02-15 02:44:33

【问题描述】：

这是一个简单的模型：

class TakingCourse(models.Model):
    course = models.ForeignKey(Course)
    term = models.ForeignKey(Term)

我不想使用 Django 创建默认主键，而是使用 course 和 term 作为主键 - 合在一起，它们唯一地标识一个元组。这是 Django 允许的吗？

在相关说明中：我试图代表用户以某些术语参加课程。有没有更好的方法来做到这一点？

class Course(models.Model):
    name = models.CharField(max_length=200)
    requiredFor = models.ManyToManyField(RequirementSubSet, blank=True)
    offeringSchool = models.ForeignKey(School)

    def __unicode__(self):
        return "%s at %s" % (self.name, self.offeringSchool)

class MyUser(models.Model):
    user = models.ForeignKey(User, unique=True)
    takingReqSets = models.ManyToManyField(RequirementSet, blank=True)
    takingTerms = models.ManyToManyField(Term, blank=True)
    takingCourses = models.ManyToManyField(TakingCourse, blank=True)
    school = models.ForeignKey(School)

class TakingCourse(models.Model):
    course = models.ForeignKey(Course)
    term = models.ForeignKey(Term)

class Term(models.Model):
    school = models.ForeignKey(School)
    isPrimaryTerm = models.BooleanField()

【参考方案1】：

您可以使用unique_together 选项。

class TakingCourse(models.Model):
    course = models.ForeignKey(Course)
    term = models.ForeignKey(Term)

    class Meta:
        unique_together = ('course', 'term')

不过，如果你这样做会更好：

class MyUser(models.Model):
    user = models.OneToOneField(User)
    takingReqSets = models.ManyToManyField(RequirementSet, blank=True)
    takingCourses = models.ManyToManyField(Course, through='TakingCourse', blank=True, null=True)
    school = models.ForeignKey(School)

class TakingCourse(models.Model):
    my_user = models.ForeignKey(MyUser)
    course = models.ForeignKey(Course)
    term = models.ForeignKey(Term)

    class Meta:
         unique_together = ('my_user', 'course')

了解one to one relationships 和extra fields on many to many relationships。