NewBookRepo creates a new BookRepo instance.

NewBookshelfRepo creates a new BookshelfRepo instance.

ErrBookAlreadyExists occurs when trying to create a book with an ID that already exists.

ErrBookNotFound occurs when a book is not found in the database.

ErrBookshelfAlreadyExists occurs when trying to create a bookshelf with an ID that already exists.

ErrBookshelfNotFound occurs when a bookshelf is not found in the database.

BookRepo implements the repository.BookRepo interface for MongoDB.

BookshelfRepo implements the repository.BookshelfRepo interface for MongoDB.