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.

1 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).


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

users[_id].valid = true;

At the beginning of the function.

  • thanks a lot, Can i do that if i want to make a function return bool value ? because i want to use it outside the remix.
    – norah
    May 14, 2020 at 15:33
  • @norah: Since variable users is declared public, you have at your disposal (implicitly generated by the compiler) function users(uint key) returns (yourStructFields). So if you add a bool field to your structure, then you'll be able to get it from Remix by calling that function. May 14, 2020 at 16:07
  • I use these two functions and it work perfect: 'function isExist(uint _id) public view returns(bool){ return users[_id].valid;} function addUser(uint _id, string memory _fname, string memory _email, uint256 _age) public returns(bool) { bool q=isExist(_id); if(q==false){ users[_id] = user(_fname,email,_age,true);}}' thanks a lot.
    – norah
    May 18, 2020 at 5:38

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