Do not allow to register twice

Question

Let's suppose I have this struct:

struct Agent {
    uint idAgent;
    address direction;
    uint[] preferences;
}
Agent[] agents;

And there's a function:

/// @notice Registra a un nuevo agente a la subasta
/// @param _idAgent identificador del agente dentro de la subasta
/// @param _preferences preferencias del agente
function regAgent(uint[] _preferences) public{
    Agent memory newAgent = Agent(numAgents, msg.sender, _preferences);
    agents.push(newAgent);
    numAgents++;
}

When an agent tries to register twice, how can I check it? I want to check that the agent is already registered but I don't want to go through the agent array. Is that possible?

Answer 1

You can try this code :

pragma solidity ^0.8.0;

contract Agent {
  struct Agent {
    uint idAgent;
    address direction;
    uint[] preferences;
}
Agent[] agents;

uint256 public numAgents;
mapping(address=>bool) _isRegistered;


/// @notice Registra a un nuevo agente a la subasta
/// @param _preferences preferencias del agente
function regAgent(uint[] memory _preferences) public{
    require(!_isRegistered[msg.sender],"sender is already registered");
    Agent memory newAgent = Agent(numAgents, msg.sender, _preferences);
    agents.push(newAgent);
    _isRegistered[msg.sender]=true;
    numAgents++;
}

}

We do two important things :

• agent Id unicity

The state variable numAgents starts from 0 and is incremented in the regAgent function after each new registration. It is passed as the idAgent parameter of the struct Agent, so each agent is guaranteed to have a unique identifier.

• agent direction address unicity

For each agent registration, we stored the sender address in the mapping _isRegistered with true as the value. The condition require(!_isRegistered[msg.sender],"sender is already registered"); checks if the sender address has already been registered in the mapping, and reverts the transaction if it's the case.