mapping and nested mapping in solidity

Mapping.sol

pragma solidity >=0.7.0 <0.9.0;

contract Mapping {
    mapping(uint => Book) public books;
    
    //nested mapping
    mapping(address => mapping(uint8 => Book)) public myBooks; 


    struct Book {
        string author;
        string title;
    }

    function addBook(uint _id, string memory _author, string memory _title) public {
        books[_id] = Book(_author, _title);
    }

    function addMyBook(uint8 _id, string memory _author, string memory _title) public {
        myBooks[msg.sender][_id] = Book(_author, _title);
    }
}