数据库：多表之间的设计以及对应类之间的关系，与数据库的操作。

当我们所做的项目要和数据库打交道的时候，总会要在数据库中创建表。

而表之间的关系：一对多，多对多，一对一，我们必须遵循数据完整性中的参照完整性。

简单提及一下，数据完整性有：实体完整性，域完整性，参照完整性。

create database dbtest;
use dbtest;
--客户和订单：一对多
create table customers(
	`id` int primary key,
	`name` varchar(100),
	`address` varchar(100)
);
create table `orders`(
	`id` int primary key,
	`num` int,
	amount float(8,2),
	customer_id int,
	constraint customer_id_fk foreign key(customer_id) references customers(id)
);
--教师和老师：多对多
create table teachers(
	id int primary key,
	name varchar(100),
	salary float(8,2)
);
create table students(
	id int,
	name varchar(100),
	grade varchar(10),
	primary key(id)
);
create table teachers_students(
	t_id int,
	s_id int,
	primary key(t_id,s_id),
	constraint t_id_fk foreign key(t_id) references teachers(id),
	constraint s_id_fk foreign key(s_id) references students(id)
);
--人和身份证：一对一
create table persons(
	id int primary key,
	name varchar(100)
);
create table idcards(
	id int primary key,
	num varchar(20),
	constraint person_id_fk foreign key(id) references persons(id)
);

表与表之间的关联关系：

一对多：

客户与订单之间的关系：一个客户可以有多个订单，但是一个订单只能属于一个客户。

CustomerDaoImpl.java

package com.xbmu.dao.impl;

import java.sql.SQLException;
import java.util.List;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import com.xbmu.domain.Customer;
import com.xbmu.domain.Order;
import com.xbmu.util.DBCPUtil;
public class CustomerDaoImpl {
	private QueryRunner qr = new QueryRunner(DBCPUtil.getDataSource());
	/**保存客户信息*/
	public void save(Customer c){
		try {
			//保存客户的基本信息到customers表
			qr.update("insert into customers (id,name,address) values(?,?,?)", c.getId(),c.getName(),c.getAddress());
			//判断客户有没有订单：如果有，保存到orders表中
			List os = c.getOrders();
			if(os.size()>0){
				for(Order o:os)
					qr.update("insert into orders (id,num,amount,customer_id) values(?,?,?,?)", o.getId(),
							o.getNum(),o.getAmount(),
							c.getId());
			}
		} catch (SQLException e) {
			throw new RuntimeException(e);
		}
		
	}
	/**查询客户信息。客户关联的订单要不要查出来？看需求。*/
	public Customer findOne(int customerId){
		try {
			//查询客户信息
			Customer c = qr.query("select * from customers where id=?", new BeanHandler(Customer.class),customerId);
			//同时查询客户的订单信息
			if(c!=null){
				List os = qr.query("select * from orders where customer_id=?", new BeanListHandler(Order.class), c.getId());
				c.setOrders(os);
			}
			return c;
		} catch (SQLException e) {
			throw new RuntimeException(e);
		}
	}
}

CustomerDaoImplTest.java

package cn.itcast.test;

import java.util.List;
import org.junit.Test;
import cn.itcast.dao.impl.CustomerDaoImpl;
import cn.itcast.domain.Customer;
import cn.itcast.domain.Order;
public class CustomerDaoImplTest {
	private CustomerDaoImpl dao = new CustomerDaoImpl();
	@Test
	public void testSave() {
		Customer c = new Customer();
		c.setId(1);
		c.setName("陈冲");
		c.setAddress("河南");
		
		Order o1 = new Order();
		o1.setId(1);
		o1.setNum(2014001);
		o1.setAmount(100);
		
		Order o2 = new Order();
		o2.setId(2);
		o2.setNum(2014002);
		o2.setAmount(1000);
		
		//建立关系
		c.getOrders().add(o1);
		c.getOrders().add(o2);
		
		dao.save(c);
	}

	@Test
	public void testFindOne() {
		Customer c = dao.findOne(1);
		System.out.println(c);
		List os = c.getOrders();
		for(Order o:os)
			System.out.println(o);
	}

}

多对多：

教师与学生的关系：一个教师可以有多个学生，一个学生可以有多个老师。因此教师与学生是多对多关系

TeacherDaoImpl.java

package com.xbmu.dao.impl;

import java.sql.SQLException;
import java.util.List;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import com.xbmu.domain.Student;
import com.xbmu.domain.Teacher;
import com.xbmu.util.DBCPUtil;
public class TeacherDaoImpl {
	private QueryRunner qr = new QueryRunner(DBCPUtil.getDataSource());
	public void save(Teacher t){
		try {
			//保存老师的基本信息
			qr.update("insert into teachers(id,name,salary) values (?,?,?)", t.getId(),t.getName(),t.getSalary());
			//保存学员信息：
			List students = t.getStudents();
			if(students.size()>0){
				for(Student s:students){
					//查询学员在不在：不在，保存学员信息
					Student stu = qr.query("select * from students where id=?", new BeanHandler(Student.class), s.getId());
					if(stu==null){
						qr.update("insert into students (id,name,grade) values(?,?,?)", s.getId(),s.getName(),s.getGrade());
					}
					//保存关系数据
					qr.update("insert into teachers_students (t_id,s_id) values(?,?)", t.getId(),s.getId());
				}
			}
		} catch (SQLException e) {
			throw new RuntimeException(e);
		}
			
	}
	public Teacher findOne(int id){
		try {
			Teacher t = qr.query("select * from teachers where id=?", new BeanHandler(Teacher.class), id);
			if(t!=null){
				//查询学生信息
				String sql = "select s.* from students s,teachers_students ts where s.id=ts.s_id and ts.t_id=?";
				List stus = qr.query(sql, new BeanListHandler(Student.class), id);
				t.setStudents(stus);
			}
			return t;
		} catch (SQLException e) {
			throw new RuntimeException(e);
		}
	}
}

TeacherDaoImplTest.java

package cn.itcast.test;

import org.junit.Test;

import cn.itcast.dao.impl.TeacherDaoImpl;
import cn.itcast.domain.Student;
import cn.itcast.domain.Teacher;

public class TeacherDaoImplTest {
	private TeacherDaoImpl dao = new TeacherDaoImpl();
	@Test
	public void testSave(){
		
		Teacher t1 = new Teacher();
		t1.setId(1);
		t1.setName("陈文");
		t1.setSalary(10000);
		
		Teacher t2 = new Teacher();
		t2.setId(2);
		t2.setName("刘悦东");
		t2.setSalary(10000);
		
		Student s1 = new Student();
		s1.setId(1);
		s1.setName("张三");
		s1.setGrade("A");
		
		Student s2 = new Student();
		s2.setId(2);
		s2.setName("李四");
		s2.setGrade("A");
		
		//建立关系
		t1.getStudents().add(s1);
		t1.getStudents().add(s2);
		
		t2.getStudents().add(s1);
		t2.getStudents().add(s2);
		
		dao.save(t1);
		dao.save(t2);
	}
	@Test
	public void testQuery(){
		Teacher t = dao.findOne(2);
		System.out.println(t);
		for(Student s:t.getStudents())
			System.out.println(s);
	}
}

一对一：

人与身份证：一个人只能有一个身份证，一个身份证只能属于一个人。

PersonDaoImpl.java

package com.xbmu.dao.impl;

import java.sql.SQLException;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import com.xbmu.domain.IdCard;
import com.xbmu.domain.Person;
import com.xbmu.util.DBCPUtil;
public class PersonDaoImpl {
	private QueryRunner qr = new QueryRunner(DBCPUtil.getDataSource());
	public void save(Person p) {
		try {
			qr.update("insert into persons (id,name) values(?,?)", p.getId(),p.getName());
			IdCard idcard = p.getIdcard();
			if(idcard!=null){
				qr.update("insert into idcards (id,num) values(?,?)", p.getId(),idcard.getNum());
			}
		} catch (SQLException e) {
			throw new RuntimeException(e);
		}
	}

	public Person findOne(int id) {
		try {
			Person p = qr.query("select * from persons where id=?", new BeanHandler(Person.class), id);
			if(p!=null){
				IdCard idcard = qr.query("select * from idcards where id=?", new BeanHandler(IdCard.class), id);
				p.setIdcard(idcard);
			}
			return p;
		} catch (SQLException e) {
			throw new RuntimeException(e);
		}
	}
}

连接数据库需要的工具类：

DBCPUtil.java

package com.xbmu.util;

import java.io.InputStream;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;

import javax.sql.DataSource;

import org.apache.commons.dbcp.BasicDataSourceFactory;

public class DBCPUtil {
	private static DataSource dataSource;
	
	static{
		try {
			Properties props = new Properties();
			InputStream in = DBCPUtil.class.getClassLoader().getResourceAsStream("dbcpconfig.properties");
			props.load(in);
			dataSource = BasicDataSourceFactory.createDataSource(props);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public static DataSource getDataSource(){
		return dataSource;
	}
	public static Connection getConnection(){
		try {
			Connection conn = dataSource.getConnection();
			return conn;
		} catch (SQLException e) {
			throw new RuntimeException(e);
		}
	}
}

PersonDaoImplTest.java

package cn.itcast.test;

import org.junit.Test;
import cn.itcast.dao.impl.PersonDaoImpl;
import cn.itcast.domain.IdCard;
import cn.itcast.domain.Person;
public class PersonDaoImplTest {
	private PersonDaoImpl dao = new PersonDaoImpl();
	@Test
	public void testSave() {
		Person p = new Person();
		p.setId(1);
		p.setName("陈冲");
		
		IdCard idcard = new IdCard();
		idcard.setNum("4201");
		
		p.setIdcard(idcard);
		
		dao.save(p);
	}

	@Test
	public void testFindOne() {
		Person p = dao.findOne(1);
		System.out.println(p.getName());
		System.out.println(p.getIdcard().getNum());
	}

}