Please I need help on how to create a custom method for a model with list_display

[Godson Rapture]

Please I am learning Django 2.0.4

Right now I am learning about Django Admin.

I got an error that the value of my list_display should not be a ManyToMany Field.

I referred back to Django official doc and I was asked to create a custom method for my model.

I tried looking for an example of how to do that, I could not see.

Here is my model.py program

 from django.db import models

class Publisher(models.Model):
    name = models.CharField(max_length=30)
    address = models.CharField(max_length=50,blank=True)
    city = models.CharField(max_length=60,blank=True)
    country = models.CharField(max_length=50,blank=True)
    website = models.URLField()
    def __str__(self):
        return self.name

class Author(models.Model):
    salution = models.CharField(max_length=10)
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=40)
    email = models.EmailField()
    headshot = models.ImageField(upload_to = "tmp")
    def __str__(self):
        return f"{self.first_name} {self.last_name}"

class Book(models.Model):
    title = models.CharField(max_length=100)
    authors = models.ManyToManyField(Author)
    publisher = models.ForeignKey(Publisher,on_delete=models.CASCADE,)
    publication_date = models.DateField()
    def __str__(self):
        return self.title

Here is my admin.py program

from django.contrib import admin
from polls.models import Book, Publisher, Author
# Register your models here.

class BookAdmin(admin.ModelAdmin):
    list_display = [
        "title",
        "authors", #a ManyToMany Field

    ]
     search_fields = [
        "Book"
    ]
    class Meta:
        model = Book

admin.site.register(Book, BookAdmin)

Can someone please help me.

Thanks.

[Daniel Germano Travieso]

Hello!

On your case, as stated on the official doc, you should just create a method on the model you want to display the ManyToMany field on the list_display that maybe returns the list of items from the ManyToMany field. Django avoids using this as it could be a potential overhead as you will run seperate queries on the database to fetch all the related many-to-many objects.

But if you are feeling adventurous, just create the method that performs that query.

i.e. On your Book model you create a method that returns the self.authors.all() set. Then you use that method's name on the list_display instead of authors.

Hope it helps.

[Godson Rapture]

Thanks very much. I have solved the problem. 

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