Shulou(Shulou.com)06/02 Report--

I have learned how to add, delete and change a single table in Django. Let's learn how to create a foreign key constraint.

Example 1

Models.py

From django.db import modelsclass UserGroup (models.Model): uid = models.AutoField (primary_key=True) caption = models.CharField (max_length=32,unique=True) ctime = models.DateTimeField (auto_now_add=True, null=True) uptime = models.DateTimeField (auto_now=True, null=True) class UserInfo (models.Model): username = models.CharField (max_length=32,blank=True,verbose_name=' user name') password = models.CharField (max_length=60 Help_text='pwd') email = models.CharField (max_length=60) test = models.EmailField (max_length=19,null=True,error_messages= {'invalid':' Please enter password'}) # user_group_id numeric user_group = models.ForeignKey ("UserGroup", to_field='uid') # (uid,catption,ctime,uptimew) user_type_choices = ((1, 'superuser'), (2 'ordinary user'), (3, 'ordinary user'), user_type_id = models.IntegerField (choices=user_type_choices,default=1)

The key statement to create a foreign key constraint is a command.

User_group = models.ForeignKey ("UserGroup", to_field='uid') # (uid,catption,ctime,uptime)

Note a few points:

To_field points to the primary key of another class

By default, he creates a cascading delete constraint, that is, if I delete a row of data in user_group, the rows associated with this uid data in the userInfo table will be deleted automatically; we can disable deletion through on_delete=models.SET_NULL

In UserInfo's table, he automatically creates a new field, user_group_id, as a foreign key field, instead of the user_group defined in our class. But interestingly, we can refer to the user_group object directly in the userInfo object in the program.

For the tables created in the database, pay attention to the field names

Let's look at an example of a call

Example 2. You can see that I can get the information of the user group table directly through row.user_group.caption, which is equivalent to performing a query operation of left join.

Views.py

Def user_info (request): if request.method = = "GET": user_list = models.UserInfo.objects.all () group_list = models.UserGroup.objects.all () return render (request, 'user_info.html', {' user_list': user_list, "group_list": group_list})

User_info.html

Add user {% for item in group_list%} {{item.caption}} {% endfor%} user list {% for row in user_list%} {{row.username}} | {{row.user_group.caption}} delete | Edit {% endfor%}

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