Django Model Unique Together example

Unique_together

This metadata is a very important one. It is equivalent to a federated constraint on the database.

For example, suppose you have a user table that holds information about the user's name, date of birth, gender, place of origin, and so on. Requirements are all users only do not repeat, but now there are several called "Zhang Wei", how to distinguish them. (Don't talk to me about the primary key, this is not the problem)

We can set no two users in the same place at the same time born and are called "Zhang Wei", the use of this joint constraint to ensure that the database can be repeatedly added users (and do not talk to me about the small probability problem). In the Django model, how do you implement this constraint?

Use Unique_together, which is the union unique.

Like what:

Unique_together = (' name ', ' Birth_day ', ' address '),)

In this way, even if there are two born on the same day, Zhang Wei, but their origin is different, that is, two different users. Once all three are the same, they are rejected by Django. This metadata is often used in the admin background and is enforced at the database level.

Unique_together receives a two-dimensional tuple ((Xx,xx,xx,...), (), (), () ...), each element is a tuple, representing a set of joint unique constraints, which can be set simultaneously with multiple sets of constraints. For convenience, you can simply use one-dimensional elements for a single set of constraints, such as:

Unique_together = (' name ', ' Birth_day ', ' address ')

The Union is the only one that cannot be used for common many-to-many fields.