Add user details to smart Contract

Question

What is the best way to store users data on smart contract? Suppose we have n number of users and we want to store each username and his other details, should we have to create a smart contract individually for every user?

Answer 1

Create a struct like so:

struct User {
    uint256 id;
    bytes32 name;
    // other stuff

    bool set; // This boolean is used to differentiate between unset and zero struct values
}

And create a mapping:

mapping(address => User) public users;

You could also use other values as index, but this is just for demonstration.

Now, to create a user, use a function like this:

function createUser(address _userAddress, uint256 _userId, bytes32 _userName) public {
    User storage user = users[_userAddress];
    // Check that the user did not already exist:
    require(!user.set);
    //Store the user
    users[_userAddress] = User({
        id: _userId,
        name: _userName,
        set: true
    });
}

And done!

EDIT As you stated in the comments, you want to store the hash of user information in a smart contract. That is even simpler: just store the hashes in a mapping.

This is the mapping you use to store the hashes in:

mapping(uint256 => bytes32) public userDataHashes;

Now, the function to set a hash for a user id becomes:

function storeUserDataHash(uint256 _userId, bytes32 _dataHash) public {
    userDataHashes[_userId] = _dataHash;
}