写合约分为一下几步：

1、需求分析：

把证书上链，证书的关键信息是：姓名、身份ID, 地址、签发时间、证书号，证书ID。

证书操作的几个步骤：1、创建，2、查询

2、代码编写：

根据需求，

a 、需要定义结构体：如下：Cert，里面就包含了所有字段。

b、定义存储变量：mapp 类型的certList，主要是通过证书唯一ID索引到证书详细信息。

c、书写创建函数：createElectronicCert，再有就是查询。checkCert

pragma solidity ^0.5.7;
// SPDX-License-Identifier: MIT

contract ElectronicCert{
address public owner;
address public manager;
constructor() public{
owner = msg.sender;
}

struct Cert{
address d_owner;
string d_name; // name
string d_ProvinceID; //Province ID
string d_certId;
uint256 d_certType;
uint256 d_createTime;
}

mapping(string => Cert) public certList; //certID -> Deposit
mapping(string => address) public certID;

function createElectronicCert(
address ply_,
string memory name_,
string memory prID_,
string memory certID_,
uint256 Type_
) public {
require(msg.sender == manager,"not manager") ;
require(certID[certID_]==address(0),"");

Cert memory plyCert = Cert(ply_,name_,prID_,certID_,Type_,now);

certID[certID_] = ply_;
certList[certID_] = plyCert;

}

function getCertInfo(string memory cID_) view public returns(
address ply_,
string memory name_,
string memory prID_,
string memory certID_,
uint256 Type_,
uint256 cTime_
){
ply_ = certList[cID_].d_owner;
name_ = certList[cID_].d_name;
prID_ = certList[cID_].d_ProvinceID;
certID_ = certList[cID_].d_certId;
Type_ = certList[cID_].d_certType;
cTime_ = certList[cID_].d_createTime;
}

function checkCert(string memory prID_,string memory certID_) view public returns(bool){
return keccak256(abi.encodePacked(certList[certID_].d_ProvinceID)) == keccak256(abi.encodePacked(prID_));
}

function setManager(address _mAddr) public{
require(msg.sender == owner,"");
require(_mAddr != address(0),"");
manager = _mAddr ;
}


}