How to check if data already exists in the table using django

Question

I am new with django framework struggling to compare value from the database. this are my tables in models.py :

class Post(models.Model):
   user = models.ForeignKey(User, on_delete=models.CASCADE,)
   title = models.CharField(max_length=200)
   content = models.TextField()
   creationDate = models.DateTimeField(auto_now_add=True)
   lastEditDate = models.DateTimeField(auto_now=True)

   def __str__(self):
       return self.title

class Votes(models.Model):
   user = models.ForeignKey(User, on_delete=models.CASCADE,)
   post_id = models.ForeignKey(Post, on_delete=models.CASCADE,)
   up_vote = models.PositiveIntegerField(default=0, validators=[MinValueValidator(0), MaxValueValidator(1)])
   down_vote = models.PositiveIntegerField(default=0, validators=[MinValueValidator(0), MaxValueValidator(1)])

   class Meta:
       unique_together = (("user","post_id"),)

I have data in the vote tabe like this:

Now what I want is to check in the above table if 'user_id' and 'post_id' already exists in the Votes tabel's rows if the exist throw a message if not add value on upvote or downvote, i gues everyone understand what i want if not please let me know.

something which i tried was this code:

def chk_table():
    user_id = request.user
    post_id = id
    votes_table = Votes.objects.filter(user_id=user_id, post_id= post_id).exists()
    return votes_table

but this function is checking in hole table not just in just in one row...

Your function chk_table is doing exactly what you have described. Not sure what the issue is — Iain Shelvington, Jun 27 '19 at 01:24
As a side note, you shouldn’t shorten your function names. check_table is far more readable — Iain Shelvington, Jun 27 '19 at 01:26
You can also use Django's get_or_create method from this [answer](https://stackoverflow.com/a/1941246/4786985). — Harish Ranganathan, May 09 '20 at 16:18

Mahmood Al Rayhan · Accepted Answer · 2019-06-27T04:10:49.390

6

Assuming that, in your urls.py

from django.urls import path
from .views import add_vote

urlpatterns = [
    path('post/<int:post_id>/vote/add/', add_vote, name='add-vote'),
]

In your views.py

from django.shortcuts import redirect, render

def add_vote(request, post_id):
    if request.method == 'POST':
        # receive your POST data here
        user_id = request.user.id
        post_id = post_id
        if not Votes.objects.filter(user_id=user_id, post_id=post_id).exists():
            Votes.objects.create(**your_data)
        redirect('your-desired-url')
    else:
        # your logic here

edited Jun 27 '19 at 04:10

answered Jun 27 '19 at 02:48

Mahmood Al Rayhan

642
5
14

thanks you really appriciate that i used this method and its worked. – Umer Jun 27 '19 at 20:52

score 2 · Answer 2 · edited Oct 21 '20 at 10:52

2

I see you already defined unique_together in Meta so you can use try except

from django.db import IntegrityError

try:
    # your model create or update code here
except IntegrityError as e: 
    if 'unique constraint' in e.message:
        # duplicate detected

edited Oct 21 '20 at 10:52

Mehedi Hasan Shifat

698
9
21

answered Jun 27 '19 at 02:43

chamoda

581
5
15

thank you for answering i used other method i am not using this because i modified the other errors. – Umer Jun 27 '19 at 20:53

How to check if data already exists in the table using django

2 Answers2