create and run the migrations for our database:

 $ python manage.py makemigrations
 $ python manage.py migrate

run demo data the command below to import the data into the database:

  $ python manage.py loaddata data.json

The CreateBook class will be used to create and save new Book entries to the database. For every mutation class we must have an Arguments inner class and a mutate() class method.

We defined an instance of the BookInput class we created earlier as our arguments, and we made it mandatory with the required=True option. After that we defined the model we are working with by doing this book = graphene.Field(BookType).

In the mutate method we are saving a new book by calling the save() method on a new Book instance created from the book_data values passed as argument.

Below you can see the implementation of the UpdateBook mutation. Add this code at the bottom of api/schema.py:

class UpdateBook(graphene.Mutation): class Arguments: book_data = BookInput(required=True)

book = graphene.Field(BookType)

@staticmethod
def mutate(root, info, book_data=None):

    book_instance = Book.objects.get(pk=book_data.id)

    if book_instance:
        book_instance.title = book_data.title
        book_instance.author = book_data.author
        book_instance.year_published = book_data.year_published
        book_instance.review = book_data.review
        book_instance.save()

        return UpdateBook(book=book_instance)
    return UpdateBook(book=None)

Let’s start the Django server:

      $ python manage.py runserver

Now visit http://127.0.0.1:8000/api/graphql in your browser. You should see the GraphIQL interface for interactive testing of the GraphQL API.

Issuing a query

   query {
          allBooks {
            id
            title
            author
            yearPublished
            review
          }
        }

The GraphQL code below is requesting all the books from the database

For single query following the query, which requests a single book by its id:

      query {
        book(bookId: 2) {
               id
               title
               author
             }
           }

for create new Book. GraphQL snippet defines a mutation that adds a new book to the database:

      mutation createMutation {
        createBook(bookData: {title: "The Chronicles", author: "Jhon Deo", yearPublished: "1980", review: 42}) {
          book {
            title,
            author,
            yearPublished,
            review
          }
        }
      }

The next GraphQL mutation updates the book with id=5:

      mutation updateMutation {
        updateBook(bookData: {id: 5, title: "The Lord of the Rings", author: "J.J.R", yearPublished: "1948", review: 20}) {
          book {
            title,
            author,
            yearPublished,
            review
          }
        }
      }

The final mutation example deletes the book with id=4 from the database:

      mutation deleteMutation{
        deleteBook(id: 6) {
          book {
            id
          } 
        }
      }