solidity – Store and retrieve data in an array in Solidity

solidity

How can store and retrieve data (many stings) while the array is an attribute of an object. I mean how to store the user info including stings in the sting[] and retrieve all User info including all the strings in the string array 

 struct User {
   uint256 id;
   //other attributes
   string[];
}

Best Answer

I've created a example smart contract to demonstrate how to push data in a struct's array. This is done in the addData function. The array's elements can be altered as demonstrated in setData.

pragma solidity 0.4.24;

contract StructStore {
    mapping(uint256 => User) users;

    struct User {
        uint256 id;
        //other attributes
        string[] data;
    }

    // Create a new user.
    function newUser(uint256 _id) public {
        // In a mapping, all elements are defined. They're just empty by default
        // So, just setting the id will create a new user;
        users[_id].id = _id;
    }

    // Pushed a piece of data to a user
    function addData(uint256 _id, string _data) public {
        users[_id].data.push(_data);
    }

    // Sets a piece of data by index
    function setData(uint256 _id, uint256 _index, string _newData) public {
        users[_id].data[_index] = _newData;
    }

    // Solidity can't return string arrays. So we'll have to provide the _dataIndex
    // Of the piece of data we want
    function getUserData(uint256 _id, uint256 _dataIndex) public view returns (string) {
        return users[_id].data[_dataIndex];
    }

    // Returns the amount of strings in a User's data array
    function getDataSize(uint256 _id) public view returns (uint256) {
        return users[_id].data.length;        
    }
}
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