Check if user exists using mapping in solidity

Question

I use solidity to store users information so before that i want to check if the user id already exist or no, Can any one help me with this code ?

i see some solution using array or require all parameters of structure and i don't prefer that, can i do this without these choices?

this function to store user information, if any one have a better code for that, i will appreciate it.

contract Contract {

    struct User{
    string fname;
    string Email;
    uint256 age;
    }


    mapping(uint => User)public users; 


 function addDoctor(uint _id, string memory fname, string memory Email,
    uint256 age) public {


         users[_id] = User(fname,email,age);

     }
 }

thanks in advanced.

Answer 1

You probably want to add bool valid or something similar in struct User, otherwise you'll need to use an implicit assumption in order to check whether or not a use exists (for example, age > 0).

UPDATE

Just to be clear, if you want to avoid handling an already-existing user, then you'll need to add:

require(!users[_id].valid);
users[_id].valid = true;

At the beginning of the function.