How do I retrieve user data once I have incremented count?

Question

I am building a web application that can store and retrieve user data. Once I add A User i increment count by 1. Once incremented the users data is added and I can fetch the data by the fetchUser(count - 1) function. Is there a way to connect this id to the users Address so that the id can be fetched when a user signs in.

    mapping (uint => Users) public users;
    mapping(address => bool) _isRegistered;

    constructor() public {
        owner = msg.sender;
        userCount = 0;
    }

function addUser(string memory _name, bool _isReg) contractIsActive() public returns (bool){
        require(!_isRegistered[msg.sender], "sender is already registered");
        emit LogUser(userCount);
        emit LogAddressUser(msg.sender);
        users[userCount] = Users({name: _name, userId: userCount, signedUp: _isReg});
        _isRegistered[msg.sender] = true;
        userCount += 1;
        return true;
    }

function fetchUser(uint _id) public view returns(string memory name, uint id, bool signed){
        name = users[_id].name;
        id = users[_id].userId;
        signed = users[_id].signedUp;

        return(name, id, signed);
    }

Answer 1

Yes, you can create a mapping which connects each address to its id (check the comments):

    mapping (uint => Users) public users;
    mapping(address => bool) _isRegistered;
    mapping(address => uint) public userId; // Here is the mapping

    constructor() public {
        owner = msg.sender;
        userCount = 0;
    }

function addUser(string memory _name, bool _isReg) contractIsActive() public returns (bool){
        require(!_isRegistered[msg.sender], "sender is already registered");
        emit LogUser(userCount);
        emit LogAddressUser(msg.sender);
        users[userCount] = Users({name: _name, userId: userCount, signedUp: _isReg});
        _isRegistered[msg.sender] = true;
        
        userId[msg.sender] = userCount; // We register it here

        userCount += 1;
        return true;
    }

function fetchUser(uint _id) public view returns(string memory name, uint id, bool signed){
        name = users[_id].name;
        id = users[_id].userId;
        signed = users[_id].signedUp;

        return(name, id, signed);
    }

// We can now retrieve an id using the address:
function fetchUserId(address _userAddress) public view returns(uint id){
    return userId[_userAddress];
    }

Beware thought that in this implementation an inexistent user will return an id of 0. You may change this behavior depending on your needs.