How to query a struct by multiple attributes in Solidity?

Question

Suppose I have the following contract:

contract UserContract {
    struct User {
        address walletAddress;
        string organisation;
        string fName;
        string lName;
        string email;
        uint index;
    }
    mapping(address => User) private users;
    address[] private userIndex;
}

I know how to write a function that returns user information corresponding to a given address, but I'd also like to write a function that can grab user info by the User's email address.

How does this work? Is my only option to create a separate mapping for this use-case that maps the User struct to a string? If so, does this mean the struct gets stored two times? Or does it only store references to that struct?

Thanks!

you can use for loop but it will take more processing , but for loop can be a solution — Uahmed, May 28 '18 at 16:21

score 4 · Accepted Answer · answered May 28 '18 at 16:41

4

If you want to do a search by either address or email (ie, NOT a composite key), then yes, the simplest option is to use two different mappings. However, struct values are stored as copies (see this for information on how mappings are stored).

To avoid extra storage for complex structs, store it in an array and use the index for the mapping values.

contract UserContract {
    struct User {
        address walletAddress;
        string organisation;
        string fName;
        string lName;
        string email;
        uint index;
    }
    User[] users;
    mapping(address => uint256) private addressMap;
    mapping(string => uint256) private emailMap; // Note this must be private if you’re going to use `string` as the key. Otherwise, use bytes32
    address[] private userIndex;
}

answered May 28 '18 at 16:41

Adam Kipnis

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Works like a charm! Thank you – Karim Stekelenburg May 30 '18 at 15:17
Could you clarify what userIndex is for, Adam Kipnis? My understanding is that addressMap already provides mapping from user's walletAddress to index in array users. – AndCode May 04 '22 at 10:21
Also why don't you make users - private? We would likely not want it to be modified directly from outside of this contract. – AndCode May 04 '22 at 10:33

How to query a struct by multiple attributes in Solidity?

1 Answers1