Tags need to be stored in the database and associated with bookmarks. So the first step in introducing tags to our project is creating a data model for tags. A tag object will only hold one piece of data, a string that represents the tag. In addition, we need to maintain the list of tags associated with a particular bookmark. You may recall from chapter 3 that we used foreign keys to associate bookmarks with users, and we called this a one-to-many relationship. However, the relationship between tags and bookmarks is not one-to-many, because one tag can be associated with many bookmarks, and one bookmark can also have many tags associated with it. This is called a many-to-many relationship, and it is represented in Django models using models.ManyToManyField.

You should be well aware by now that data models go into bookmarks/models.py, so open the file and add the following Tag class to it:

class Tag(models.Model):
  name = models.CharField(maxlength=64, unique=True)
  bookmarks...