JDBC 进阶（未完结）

 一 实体类和ORM

对指定的对象的属性封装

package com.ax.advance.pojo;

public class Employee {

    private Integer id;
    private String degree;
    private String major;
    private String school1;
    private String school2;
    private String school3;
    private Integer userId;

    public Employee(Integer id, String degree, String major, String school1, String school2, String school3, Integer userId) {
        this.id = id;
        this.degree = degree;
        this.major = major;
        this.school1 = school1;
        this.school2 = school2;
        this.school3 = school3;
        this.userId = userId;
    }

    public Employee() {
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getDegree() {
        return degree;
    }

    public void setDegree(String degree) {
        this.degree = degree;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }

    public String getSchool1() {
        return school1;
    }

    public void setSchool1(String school1) {
        this.school1 = school1;
    }

    public String getSchool2() {
        return school2;
    }

    public void setSchool2(String school2) {
        this.school2 = school2;
    }

    public String getSchool3() {
        return school3;
    }

    public void setSchool3(String school3) {
        this.school3 = school3;
    }

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }
    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", degree='" + degree + '\'' +
                ", major='" + major + '\'' +
                ", school1='" + school1 + '\'' +
                ", school2='" + school2 + '\'' +
                ", school3='" + school3 + '\'' +
                ", userId=" + userId +
                '}';
    }
}

数据封装在对象当中

package com.ax.advance;

import com.ax.advance.pojo.Employee;

import java.sql.*;

public class JDBCa {
    public static void main(String[] args) throws SQLException {
        //获取连接对象
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/itheima", "root", "tan2179432748");
        //预编译SQL语句
        PreparedStatement preparedStatement = connection.prepareStatement("select * from tb_user_edu where degree = ?");
        //为问号占位符赋值，并执行SQL语句，接收返回的结果集
        preparedStatement.setString(1, "本科");
        //处理结果集
        ResultSet resultSet = preparedStatement.executeQuery();
        //遍历结果集
        Employee employee = null;
        while (resultSet.next()) {
            int id = resultSet.getInt("id");
            String degree = resultSet.getString("degree");
            String major = resultSet.getString("major");
            String primaryschool = resultSet.getString("primaryschool");
            String middleschool = resultSet.getString("middleschool");
            String university = resultSet.getString("university");
            int userId = resultSet.getInt("userid");

            //封装对象
            employee = new Employee(id, degree, major, primaryschool, middleschool, university, userId);
            System.out.println(employee);
        }
        //资源的释放(先开后放)
        resultSet.close();
        preparedStatement.close();
        connection.close();

    }
}

对象再封装在集合当中

package com.ax.advance;

import com.ax.advance.pojo.Employee;

import java.sql.*;
import java.util.ArrayList;

public class JDBCb {
    public static void main(String[] args) throws SQLException {
        
        //获取连接对象
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/itheima", "root", "tan2179432748");
        
        //预编译SQL语句
        PreparedStatement preparedStatement = connection.prepareStatement("select * from tb_user_edu where degree = ?");
        
        //为问号占位符赋值，并执行SQL语句，接收返回的结果集
        preparedStatement.setString(1, "本科");
        
        //处理结果集
        ResultSet resultSet = preparedStatement.executeQuery();
        
        //创建集合存储对象
        ArrayList<Employee> employees = new ArrayList<>();
        
        //遍历结果集
        Employee employee = null;
        while (resultSet.next()) {
            employee = new Employee();
            employee.setId(resultSet.getInt("id"));
            employee.setDegree(resultSet.getString("degree"));
            employee.setMajor(resultSet.getString("major"));
            employee.setSchool1(resultSet.getString("primaryschool"));
            employee.setSchool2(resultSet.getString("middleschool"));
            employee.setSchool3(resultSet.getString("university"));
            employee.setUserId(resultSet.getInt("userid"));
            employees.add(employee);
        }
        //输出
        employees.forEach(System.out::println);


    }
}

二 主键回显

主键回显指在数据库插入操作后，自动获取数据库生成的主键值（如自增ID、序列值等），并将其回填到程序中的对象或变量中。其核心目的是解决多表关联插入时主键依赖问题，例如：主表插入后需获取自增ID，才能将子表数据的外键关联到该ID