[区块链]以太坊智能合约开发（五）：Solidity成绩录入智能合约实验

1 编写智能合约

每个学生分别部署合约Student.sol ，保证只有自己可以修改姓名。老师部署合约StudentScore.sol，用于录入学生成绩，查询学生信息。查询学生信息时，需要调用学生部署的合约Student.sol。
student.sol合约，用于学生对自己信息进行管理。

• 学生的基本信息作为状态变量：

	pragma solidity ^0.4.0;
	contract Student{
	    string studentID;
	    string studentName;
	    address owner;
	}

• 声明构造函数，在构造函数中将owner设置为调用者的address：

	constructor(string _studentID, string _stdentName) public{
		studentID = _studentID;
		studentName = _stdentName;
		owner = msg.sender;
	}

• 声明函数修饰器，可以将其加在函数中，在函数执行前进行判断，来检查调用者是否为学生本人，只有本人才能调用该函数：

	modifier onlyOwner(){
    	require(msg.sender == owner,"only owner can call this function");
    	_;
	}

• get和set方法，其中set方法加入了函数修饰器：

    function getStudentIDandName() public constant returns(string,string) {
    	return (studentID,studentName);
    }

    function setStudentIDandName(string _studentID,string _studentName) public onlyOwner {
    	studentID = _studentID;
    	studentName = _studentName;
    }

Teacher.sol合约，用于录入、查询学生成绩

• 导入Student合约：

	pragma solidity ^0.4.11;
	import "./Student.sol";

• 学生的相关成绩作为状态变量，totalScore为全班总成绩，studentCount全班学生数量，owner部署合约的账户地址。同时声明映射studentAddrMap，studentScoreMap，将学生ID分别映射为学生地址和学生成绩。事件studentNotExistsEvent用于存储学生ID号

	contract StudentScore{
	    uint totalScore;
	    uint studentCount;
	    address owner;
	    mapping(string => address) studentAddrMap;
	    mapping(string => uint) studentScoreMap;
	    event studentNotExistsEvent(string studentID);
	}

• 声明自定义修饰符onlyOwner，只有老师地址才能执行这些函数。

	modifier onlyOwner(){
        require(msg.sender == owner,"only owner can call this function");
        _;
    }

• 函数addStudentScore，modifyScoreByStudentId分别用于老师添加或修改学生成绩：

    function addStudentScore(string studentID, address student, uint score) public onlyOwner {    
        studentAddrMap[studentID] = student;
        studentScoreMap[studentID] = score;
        totalScore += score;
        studentCount ++;
    }
    
    function modifyScoreByStudentId(string studentID, uint score) public onlyOwner{
        if(!studentExists(studentID)) {
            studentNotExistsEvent(studentID);
            return;
        }
        totalScore -= studentScoreMap[studentID];
        studentScoreMap[studentID] = score;
        totalScore += score; 
    }

• 函数getAvgScore用于查询全班学生平均成绩，函数studentExists用于判断学生ID是否存在，函数getScoreByStudentID用于学生查询自己的成绩。

    function getAvgScore() public view returns(uint){    
        return totalScore / studentCount;
    }
    function studentExists(string studentID) public view returns(bool){
        address student = Student(studentAddrMap[studentID]);
        if(student == 0x00){
            return false;
        }else{
            return true;
        }
    }
    function getScoreByStudentID(string studentID) public constant returns(string, string, uint){
        if(!studentExists(studentID)) {
            studentNotExistsEvent(studentID);
            return;
        }
        Student student = Student(studentAddrMap[studentID]);
        var studentName = student.getStudentName();
        uint score = studentScoreMap[studentID];
        return(studentID, studentName, score);
    }