Django Interview Preparation

  Difference between select_related and prefetch_related Reducing SQL queries is one of the first steps when optimizing a Django project. There are two powerful methods included in the Django ORM to help us that can boost performance by creating a single more complex QuerySet rather than multiple, smaller queries. In this project we will understand about  select_related and prefetch_related.  Django use these two orm method to reduce sql queries in database based on different scenario.  select_related Lets assume  this two model we have.  class Author ( models . Model ): name = models . CharField ( max_length = 200 ) def __str__ ( self ): return self . name class Courses ( models . Model ): name = models . CharField ( max_length = 200 ) author = models . ForeignKey ( Author , on_delete = models . CASCADE , related_name = 'courses' ) def __str__ ( self ): return self . name Here we have two mode. ...

 Django Slugs and UUIDs Why We have to Use UUID or SlugFlied: The django default id or primary_key( pk ) is currently  auto-incrementing id. Among other concerns, it tells a potential hacker exactly how many records you have in your database; it tells them exactly what the id is which can be used in a potential attack; and there can be synchronization issues if you have multiple front-ends.  There are two alternative approaches. UUID and SlugFiled UUIDField: A field for storing universally unique identifiers. Uses Python’s UUID class. When used on PostgreSQL and MariaDB 10.7+, this stores in a uuid datatype, otherwise in a char(32). Example Code: class UserProfile ( models . Model ): id = models . UUIDField ( primary_key = True , default = uuid . uuid4 , editable = False ) name = models . CharField ( max_length = 500 ) email = models . EmailField () def __str__ ( self ): return self . name def get_absolute_url ( self ): ...

 Django pk VS id If you don’t specify primary_key=True for any fields in your model, Django will automatically add an IntegerField to hold the primary key, so you don’t need to set primary_key=True on any of your fields unless you want to override the default primary-key behavior. The primary key field is read-only. If you change the value of the primary key on an existing object and then save it, a new object will be created alongside the old one Example: class UserProfile ( models . Model ): name = models . CharField ( max_length = 500 ) email = models . EmailField ( primary_key = True ) def __str__ ( self ): return self . name suppose we have this model. In this model we have make email field as primary key. now django default primary key id field will be gone. It'll remove from database. we can not query as   UserProfile.objects.get(id=1) after make email as primary key this query will throw an error.  Now we have to use pk  Us...