{"id":6275,"date":"2022-12-27T07:57:40","date_gmt":"2022-12-27T07:57:40","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=6275"},"modified":"2023-01-19T02:05:30","modified_gmt":"2023-01-19T02:05:30","slug":"django-manytomanyfield-through","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/django-tutorial\/django-manytomanyfield-through\/","title":{"rendered":"Django ManyToManyField Through"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to add extra fields to the ManyToManyField<\/code> using the through argument.<\/p>\n\n\n\n

In a many-to-many relationship<\/a>, multiple rows in a table are associated with multiple rows in another table. To establish a many-to-many relationship, relational databases use a third table called the join table and create two one-to-many relationships<\/a> from the source tables.<\/p>\n\n\n\n

Typically, the join table contains the id values of the source tables so that rows in one table can relate to the rows in the other table.<\/p>\n\n\n\n

Sometimes, you may want to add extra fields to the join table. For example, each employee may have multiple jobs during his\/her career. <\/p>\n\n\n\n

To track when an employee takes a job, you can add the begin_date<\/code> and end_date<\/code> fields to the join table.<\/p>\n\n\n\n

To do that in Django, you use the ManyToManyField<\/code> with the through<\/code> argument. <\/p>\n\n\n\n

For example, the following shows how to associate an employee with multiple jobs through the assignments:<\/p>\n\n\n

class<\/span> Employee<\/span>(models.Model)<\/span>:<\/span>\n   # ...<\/span>\n\nclass<\/span> Job<\/span>(models.Model)<\/span>:<\/span>\n    title = models.CharField(max_length=255<\/span>)\n    employees = models.ManyToManyField(Employee, through='Assignment'<\/span>)\n\n    def<\/span> __str__<\/span>(self)<\/span>:<\/span>\n        return<\/span> self.title\n\n\nclass<\/span> Assignment<\/span>(models.Model)<\/span>:<\/span>\n    employee = models.ForeignKey(Employee, on_delete=models.CASCADE)\n    position = models.ForeignKey(Job, on_delete=models.CASCADE)\n    begin_date = models.DateField()\n    end_date = models.DateField(default=date(9999<\/span>, 12<\/span>, 31<\/span>))<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
How it works.<\/p>\n\n\n\n