What is Query?

What is Query Set?

Actually when one record about an entity is stored in the table, is called an object. When multiple objects are stored in the table they are a set of objects, to retrieve that set of objects, we called query a query set. Query set returned the set of objects the result of a query set may be zero if there is no record in a database, one or many filters.

When we use a query set to get a set of objects it may be filtering to get the specific record, for example, you want to get all the students with the name of ‘Faisal’, so it will return a set of objects because it will contain multiple records which contain ‘Faisal’ name.

Or slicing can be used in the query set to get a required record for example if you want to get last or first records or between records etc.

Or we can also use ordering techniques, in which we can order the records as Ascending or descending or in order to down to up alphabetical or down to up number etc.

What is Django Query Set API?

It is the query that is used to communicate with a database to perform different operations on the data stored in the tables.

WORKING with Django Query Set API

As we have discussed we can perform different operations on that database table data to get the required record about an entity.

So, in the following part, we will create a reocrd using Djagno Query set API.

1. Create an object

This query will create an object with the following information as we have assigned.

from app_name.models import Person

person_Info = Person(name=’Lala’, email=’lala@gamil.com’)

person_Info .save() # it will save all the information

2. Retrieve an object

If you want to get all the objects stored in the specific table, you can use the following query, where Person is the table name in this case.
Person.objects.all()

3. Update object

In this example, you will be cleared how you can update a record in the database table using query set API

Person.objects.filter(pk=mention_id).update(column_name=’new_value’)

It will udpat the record for a specefic id with new value in specefic column you mention.

OR

You can use anpother method also, if you want to update anything else in the table.

return_obj = Person.objects.get(pk=mention_id)
return_obj .name = “new_value”
return_obj .save()

So, it will also update the record. It is the same logic but we have broken the line in 4.

4. Delete an object

As we have mentioned we can perform all the crud operations with Django Query Set API. So the record or set of records you can delete using query set API.

The following query will delete the obejcts in the Person table.

Person.objects.all().delete()

Or to delete a specific record in the person table, you can filter at first then delete the specific record.

Person.objects.filter(pk=mention_Id()).delete()

5. Filter object

With the default manager class, it is the same as:

It is very important, when we want to update or delete, we have to find or filter specific records which we want to update or delete, then we use filter query.

If we run the following query, all the records will be retrieved with the city name ‘DIKHAN’

Person.objects.all().filter(city=’DIKHAN’)

7. Order by object

We can retrieve the object in a different order, ascending or descending. For example, you want to get all the student’s names in alphabetical order, then will use the order by the query.

This command will return all the person belong from city Paharpurin descending order

Person.objects.filter(city=’Paharpur).order_by(‘-id’)