Updated May 22, 2023
Introduction to Django exists
We know that Django provides many different types of features to the user, which is one of Django’s features. We must implement advanced methods to get specific results when working with data. Normally exists() is used to search the related object membership inside the query set, showing if any specified object exists in the query set. In other words, we can say that exists () is used for large query sets and is an efficient method to handle data in Django.
Overview of Django exists
Django’s QuerySet API gives an extensive cluster of strategies and capacities for working with information. This section will examine the normal QuerySet strategies, field queries, and total capabilities, and how to fabricate more mind-boggling questions with question articulations and Query set() objects. Returns True, assuming the QuerySet contains any outcomes.
While working with Django ORM, we frequently experience the issue regardless of whether the object exists. For instance, there is no API to check to assume that items exist in the object in a one-to-one relationship. Instead, exists is a Subquery subclass that utilizes a SQL EXISTS explanation. The reason it often performs better than a subquery is that the information base can stop assessing the subquery when it finds the first matching line.
Why does Django exist?
Now let’s see why we need to use exists as follows:
Usually, when we communicate with a QuerySet, you’ll utilize it by binding channels. To make this work, most QuerySet strategies return new querysets. We extensively cover these strategies later in this section.
The main reason behind this guidance is that queryset.count() performs a SQL operation that examines each row in the dataset table to calculate the total. Then again, queryset.exists() essentially peruses a solo record in the most upgraded manner.
- Elimination of ordering
- Elimination of gathering
Clear any dev-characterized select_related and particular from the queryset.
The QuerySet class has two public credits you can use for reflection: Ordered.
Valid assuming the QuerySet is requested — for example, it has an order_by() proviso or a default requesting on the model.
The inquiry boundary to QuerySet exists so that specific question subclasses can reproduce inside the question state. The worth of the boundary is a misty portrayal of that question state and isn’t important for a public API. If you want to check whether the consequence of the QuerySet exists, don’t involve QuerySet as a boolean worth or queryset.count() > 0. Use queryset.exists(), all things considered.
The strategy exists() returns True, assuming the QuerySet contains any outcomes, and False if not. It attempts to solve the question in the least complex and quickest way imaginable but executes almost a similar inquiry as a typical QuerySet question. Exists() helps connect with item participation in a QuerySet and any articles in a QuerySet, especially about a huge QuerySet.
Working of Django exists
Given below shows how we can work with what exists in Django as follows:
We are aware that it is used to return true if one or more objects are present inside the QuerySet, and it returns false if our QuerySet is empty.
Example:
Let’s see a different example for better understanding as follows:
On the command line, we need to execute the following statement.
Code:
student.objects.create(studname =name)But we can see here that first, we need to import models.
Code:
from student.models import StudentNow everything is ok; let’s see the result on the command line as below screenshot.
Output:
Suppose we need to find whose name is Sachin, then we need to use the following statement.
Code:
name = Student.objects.get(studname = 'Sachin')The result of the above statement can be seen in the screenshot below.
Output:
In the above example, we retrieve Sachin from the database; After that, we need to check if this is a single object by ensuring that he is one of the Sachin instances presented in the database, using the following statement.
Code:
from student.models import Student
user = Student.objects.filter(studname = 'Sachin')
user.filter(pk=name.pk).exists()Explanation:
In the above example, first, we need to import the model that we already created after trying to retrieve Sachin from the database by using the second statement. Then the third statement is then used for checking whether this is a single or multiple object. The above implementation’s result in the screenshot below is as follows.
Output:
Now let’s see for another case: if Johan is not present inside the database, we get what we get as follows.
Code:
from student.models import Student
user = Student.objects.filter(studname = 'Johan').exists()Explanation:
The above implementation’s result in the screenshot below is as follows.
Output:
How to Check if Django exists?
Now let’s see how we can check if it exists in Django.
It is a conditional statement used to handle the condition; in other words, we can say that if an object is present inside the object, then we print some message. If the object is not present inside the database, it prints the other part.
Example:
Now let’s see an example.
Code:
from student.models import Student
user = Student.objects.filter(studname = 'Johan').exists()
if queryset.contains(user)
print('This object present inside the query set')Explanation:
- In the above example, we try to implement the if exist () method; here, we import the model we already created. After that, we try to fetch the object from that database using the exits() method. In the end, we use the if statement to verify the result.
- That means if Johan is present inside the database, it shows a message. The above implementation’s end result in the screenshot below is as follows.
Output:
Conclusion
With the help of the above article, we saw Django. From this article, we saw basic things about Django exist, the features and examples of Django exist, and how we use it in Django.
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