How can I return multiple value?

Question

How can I return multiple value. If I get string ,it return the last value. How to get string ,its return multiple value?

pragma solidity ^0.8.0 ;

contract Simple {
    mapping(string => uint)  serialID;
    
    function set(string memory _id ,uint value_a ,uint value_b ,uint value_c ,uint value_d) public {
        serialID[_id] = value_a;
        serialID[_id] = value_b;
        serialID[_id] = value_c;
        serialID[_id] = value_d;
    }

    function get(string memory _id) public view returns(uint) {
        return serialID[_id];
    } 
}

Answer 1

In your set function you are updating the value of the same key : so it will only store the last value (you are replacing value_a with value_b, value_b with value_c and so on), because mapping will assing one key to one value . the function bellow do the same thing:

function set(string memory _id , uint value_d) public {

    serialID[_id] = value_d;

}

if you want to assing one key to mutiple value you should use a struct:

 struct Test{
       uint a;
       uint b;
       uint c;
       uint d;
   }
   mapping(string => Test) public serialID;
   function set(string memory _id){
      Test storage test = Test(1, 2, 3, 4);
      serialID[_id] = test;
   }
   
   function get(string memory _id) public view returns(uint, uint, uint, uint){

    return serialID[_id];
} 

i hope that helps, good luck !

Answer 2

Another solution for solve your issue is using uint[] array into mapping and change set function signature adding a unique uint array parameter.

In conclusion, your smart contract should be similar to this:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0 ;

contract Simple {
    mapping(string => uint[]) serialID;
    
    function set(string memory _id, uint[] memory _values) public {
        serialID[_id] = _values;
    }

    function get(string memory _id) public view returns(uint[] memory) {
        return serialID[_id];
    } 
}