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<Order> 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>(Customer.class),customerId);
//同时查询客户的订单信息
if(c!=null){
List<Order> os = qr.query("select * from orders where customer_id=?", new BeanListHandler<Order>(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<Order> 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<Student> 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>(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>(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<Student> stus = qr.query(sql, new BeanListHandler<Student>(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>(Person.class), id);
if(p!=null){
IdCard idcard = qr.query("select * from idcards where id=?", new BeanHandler<IdCard>(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());
}

}