What is doing __str__ function in Django?

Question

I'm reading and trying to understand django documentation so I have a logical question.

There is my models.py file

from django.db import models  # Create your models here.   class Blog(models.Model):     name = models.CharField(max_length=255)     tagline = models.TextField()      def __str__(self):         return self.name    class Author(models.Model):     name = models.CharField(max_length=255)     email = models.EmailField()      def __str__(self):         return self.name    class Post(models.Model):     blog = models.ForeignKey(Blog)     headline = models.CharField(max_length=255)     body_text = models.TextField()     pub_date = models.DateField()     mod_date = models.DateField()     authors = models.ManyToManyField(Author)     n_comments = models.IntegerField()     n_pingbacks = models.IntegerField()     rating = models.IntegerField()      def __str__(self):         return self.headline 

What is doing here each __str__ function in each class? What is the reason I need those functions in it?

Answer 1

You created a Blog model. Once you migrate this, Django will create a table with "name" and "tagline" columns in your database.

If you want to interact with the database with the model, for example create an instance of the model and save it or retrieve the model from db,

def __str__(self):     return self.name  

will come handy. Open the python interactive shell in your project's root folder via:

python manage.py shell 

Then

from projectName.models import Blog  Blog.objects.all() # will get you all the objects in "Blog" table 

Also, when you look at the models in your admin panel, you will see your objects listed, with the name property.

The problem is, the return will look like this if you did not add that function:

<QuerySet [<Blog:>,<Blog:>,<Blog:>....] 

So you will not know what those objects are. A better way to recognize those objects is retrieving them by one of its properties which you set it as name. This way you will get the result as follow:

 <QuerySet [<Blog:itsName>,<Blog:itsName>,<Blog:itsName>....] 

If you want to test this out, run python manage.py shell and run:

from projectName.models import Blog  # The below will create and save an instance. # It is a single step. Copy-paste multiple times. Blog.objects.create(name="first",tagline="anything") Blog.objects.all() # check out the result 

Answer 2

The __str__ method just tells Django what to print when it needs to print out an instance of the any model. It is also what lets your admin panel, go from this

Note: how objects are just plainly numbered

to this

.

Note: proper object names here

You could choose what to show in the admin panel, as per your choice. Be it a field value or a default value or something else.