How Retrieve a specific entity on mapping

Question

I'm trying to start a stacking smart contract. Each user can stake different ERC20 Token.

I'm using follwing struct :

   struct Token {
        address tokenAddress;
        uint256 stakedAmount;
        uint lastTransactionDate;
        bool isUsed;
    }

I define a relation User-Token with :

mapping(address => Token) stakingUserBalance;

On my stake function I need to store an ERC20 token for user :

function stakeToken(address tokenAddress, uint256 amount) public {
    require(amount > 0, "You cannot stake 0 token");

    //Transfer amount to smartcontract
    IERC20(tokenAddress).transferFrom(msg.sender, address(this), amount);

    //Update user balance
    Token storage userToken = stakingUserBalance[msg.sender];
    userToken.lastTransactionDate = block.timestamp;
    userToken.stakedAmount += amount;
  

    //fire event
    emit TokenStaked(tokenAddress, amount);
}

So my question is : how get a specific token address in stakingUserBalance to update the value of stakedAmount for right token ?

thanks for your help

Answer 1

As in your use case each user (represented by an address) can stake a token (represented by an address) for which you store the information (represented by the Token struct) I would recommend to adjust your mapping structure to:

// user address -> token address -> information
mapping(address => mapping(address => Token)) stakingUserBalance;

This allows you to access the information by using the following:

Token storage userToken = stakingUserBalance[msg.sender][tokenAddress];

Answer 2

The way you've defined the Token and stakingUserBalance, a user can only stake once type of token. User address is used as the only unique key. You'd have to restructure the data structure to use address-token as a unique combination.

One way would be to use a mapping of mapping.

mapping (address => mapping(address => Token)) public stakedTokens;

This would let create a mapping of tokenAddress => Token for each user address. This way, you can support multiple tokens for each user.

To access a token balance, you can use the following method.

stakedTokens[userAddress][tokenAddress].stakedAmount;

Hope this clarifies your questions.