Solidity：学生认证架构

Question

I recently did a course on uDemy and get the first concepts. I'm starting to build a real-life app for a training center. I want to register in the blockchain that Jhon Doe, ID (document) xxxx, approved the course "Master of blockchain" at a specific date, and also register the "expiration date" for the certification/permission.

In PHP I would create an array like this:

$certifications[123456] = [
    [
    "name" => "Jhon",
    "lastName" => "Doe",
    "courseName" => "Blockchain master",
    "Expiration date" => "2022-01-01"
    ],
    [
    "name" => "Jhon",
    "lastName" => "Doe",
    "courseName" => "Just another course",
    "Expiration date" => "2021-01-01"
    ]
];

With the output:

array (size=1)
  123456 => 
    array (size=2)
      0 => 
        array (size=4)
          'name' => string 'Jhon' (length=4)
          'lastName' => string 'Doe' (length=3)
          'courseName' => string 'Blockchain master' (length=17)
          'Expiration date' => string '2022-01-01' (length=10)
      1 => 
        array (size=4)
          'name' => string 'Jhon' (length=4)
          'lastName' => string 'Doe' (length=3)
          'courseName' => string 'Just another course' (length=19)
          'Expiration date' => string '2021-01-01' (length=10)

Furthermore, I want to create a function to find by document ID the certification he/she did.

Needless to say that I want to keep it on memory on a persistent way, using gas if necesary.

I thought in create a mix between mapping and array for this, maybe struct... But I've the feeling that I'm on the wrong way.

So... Anybody can guide me or send me a similar example to check how to approach?

Thanks in advance!

Edition 1:

I write this code following some tips and got it working except 2 thing:

pragma solidity 0.6.6;
pragma experimental ABIEncoderV2;
// SPDX-License-Identifier: MIT

import 'https://github.com/OpenZeppelin/openzeppelin-solidity/contracts/math/SafeMath.sol';

contract Certification {
    using SafeMath for uint256;
    
    address private owner;
    
    struct Certificate {
        string name;
        string lastname;
        string certificationName;
        string instructorName;
        uint256 dueDate;
        uint256 expirationDate;
    }
    
    
    Certificate[] public certifications;

    mapping(uint => uint) public dniToCertification;
    
    event certificateSubscribed(string name, string lastname, uint dni, string certification, string instructor, uint256 date, uint256 untilDate);
    
    constructor() public {
        owner = msg.sender;
    }
    
    modifier isOwner() {
        require(owner == msg.sender);
        _;
    }
    
    function subscribeCertificate(
        string memory name,
        string memory lastname,
        uint dni,
        string memory certificationName,
        string memory instructorName,
        uint256 dueDate,
        uint256 expirationDate) public isOwner {
            
        certifications.push(Certificate(
           name,
           lastname,
           certificationName,
           instructorName,
           dueDate,
           expirationDate
        ));
            
        Certificate storage certification; //certification will be an instance of Struct Certificate
        
        certification.name = name;
        certification.lastname = lastname;
        certification.certificationName = certificationName;
        certification.instructorName = instructorName;
        certification.dueDate = dueDate;
        certification.expirationDate = expirationDate;
        
        uint id = certifications.length - 1;
    
        dniToCertification[dni] = id;
        
        
        emit certificateSubscribed(name, lastname, dni, certificationName, instructorName, dueDate, expirationDate);
    }
    
    function checkCertificateByDni(uint id) public view returns (Certificate memory) {
        return (certifications[dniToCertification[id]]);
        
    }
    
}

1. Mapping is not iterable, so I have to return the entire Struct objects using experimental ABIEncoderV2
2. I got error at the second time I want to call subscribeCertificate with not detailed information...

Answer 1

I suggest save the certificate array in Structs and have a mapping for address and list of documents ids users have.

//certificate object
struct Certificate {
    string name;
    string lastName;
    string courseName;
    uint256 expirationDate;
}

// you can save all certifications on this array.
Certificate[] public certifications;

//save every address certifications and address
mapping(address => uint256[]) public userCertifications;

Usage example:

// get certificate  by id
certifications[id]

// get user certifications-> return array of user certifications
userCertifications[msg.sender] or userCertifications[address]

Edition 1 answer

I changed your code to this and I think it can work for you!

pragma solidity 0.6.6;
// SPDX-License-Identifier: MIT

import 'https://github.com/OpenZeppelin/openzeppelin- 
solidity/contracts/math/SafeMath.sol';

contract Certification {
using SafeMath for uint256;

address private owner;

struct Certificate {
    string name;
    string lastName;
    string certificationName;
    string instructorName;
    uint256 dueDate;
    uint256 expirationDate;
}


Certificate[] public certifications;

mapping(uint => uint) public dniToCertification;




event certificateSubscribed(string name, string lastname, uint dni, string certification, string instructor, uint256 date, uint256 untilDate);

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

modifier isOwner() {
    require(owner == msg.sender);
    _;
}

function subscribeCertificate(
    string memory name,
    string memory lastname,
    uint dni,
    string memory certificationName,
    string memory instructorName,
    uint256 dueDate,
    uint256 expirationDate) public isOwner {
        
        
        certifications.push(Certificate(
           name,
           lastname,
           certificationName,
           instructorName,
           dueDate,
           expirationDate));

        uint id = certifications.length - 1;
        
        dniToCertification[dni] = id;
        
        
        emit certificateSubscribed(name, lastname, dni, certificationName, instructorName, dueDate, expirationDate);
}

}

Copy and paste it remix and you see you have 2 methods one to get a certificate and another to get a certificate by dni. Also, you can't get an array of structs in solidity and you must do it on the client-side and by using loop get the whole certificates.