Question

我试图了解如何正确设置我的模型以建立多对多关系，我注意到创建模型时有一个ManyToManyField选项，但我似乎无法理解它的逻辑以及如何使其正常工作。我想分享我的代码并进行解释。

from django.db import models

class Major(models.Model):
    name = models.CharField(max_length=30, db_index=True)

class School(models.Model):
    name = models.Charfield(max_length=50, db_index=True)
    majors = models.ManyToManyField(Major)

class Professor(models.Model):
    ProfessorIDS = models.IntegerField()
    ProfessorName = models.CharField(max_length=100)
    ProfessorRating = models.DecimalField(decimal_places=2,max_digits=4)
    NumberOfRatings = models.CharField(max_length=50)
    school = models.ForeignKey(School , on_delete=models.CASCADE)
    major = models.ForeignKey(Major , on_delete=models.CASCADE)

请注意，学校表（班级）具有多对多的专业，这实际上是我想要的，其目标是建立一个数据库，以允许在单个学校下存储多个专业。

经过研究，我得出结论认为这没有道理，创建一个Bridge Table会更好，所以我决定像这样创建我的模型...

from django.db import models

class Major(models.Model):
    name = models.CharField(max_length=30, db_index=True)

class School(models.Model):
    name = models.Charfield(max_length=50, db_index=True)


class School_Majors(models.Model):
    school = models.ForeignKey(School, on_delete=models.CASCADE)
    major = models.ForeignKey(Major, on_delete=models.CASCADE)

class Professor(models.Model):
    ProfessorIDS = models.IntegerField()
    ProfessorName = models.CharField(max_length=100)
    ProfessorRating = models.DecimalField(decimal_places=2,max_digits=4)
    NumberOfRatings = models.CharField(max_length=50)
    school = models.ForeignKey(School , on_delete=models.CASCADE)
    major = models.ForeignKey(Major , on_delete=models.CASCADE)

这不是设置数据库以从学校添加和删除多个专业的更合适的方法吗？

Answer 1

最好创建一个桥接表

ManyToManyField就是这样做的。您的两个摘要在功能上是相同的。

如果您可能希望在穿透表上有一些额外的数据（在Django世界中被称为），例如第一次提供专业时的现场记录，则可以使用through参数ManyToManyField，如下：

from django.db import models

class Major(models.Model):
    name = models.CharField(max_length=30, db_index=True)


class School(models.Model):
    name = models.CharField(max_length=30, db_index=True)
    majors = models.ManyToManyField(Major, through='SchoolMajor')


class SchoolMajor(models.Model):
    major = models.ForeignKey(Major, on_delete=models.CASCADE)
    school = models.ForeignKey(School, on_delete=models.CASCADE)
    first_offered = models.DateField()

改编自here。

Django的型号多到许多与桥表

1 个答案: