本文主要讲了使用Mybatis实现关联查询，分为一对一和一对多两种情况，最后并对ResultMap进行一个简要说明。

一、创建表、分析

下面是两表，一个是顾客表，一个是车票表。一个顾客可以对应多张车票，但是一张车票只能对应一个顾客

t_customer：顾客表，一个顾客可以对应多张车票

t_ticket：车票表，一张车票只能对应一个顾客

1、创建数据表及插入初始数据

创建数据表

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use test;
DROP TABLE IF EXISTS t_customer;
CREATE TABLE t_customer(
customerId INT PRIMARY KEY AUTO_INCREMENT,
customerName VARCHAR(20) NOT NULL,
customerTel INT NOT NULL
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
DROP TABLE IF EXISTS t_ticket;
CREATE TABLE t_ticket(
ticketId INT PRIMARY KEY AUTO_INCREMENT,
ticketAddress VARCHAR(50) NOT NULL,
ticketPrice INT NOT NULL,
ticketCId INT NOT NULL
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

use test;DROP TABLE IF EXISTS t_customer;CREATE TABLE t_customer(customerId INT PRIMARY KEY AUTO_INCREMENT,customerName VARCHAR(20) NOT NULL,customerTel INT NOT NULL)ENGINE=InnoDB DEFAULT CHARSET=utf8;DROP TABLE IF EXISTS t_ticket;CREATE TABLE t_ticket(ticketId INT PRIMARY KEY  AUTO_INCREMENT,ticketAddress VARCHAR(50) NOT NULL,ticketPrice INT NOT NULL,ticketCId INT NOT NULL)ENGINE=InnoDB DEFAULT CHARSET=utf8;

插入数据：

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use test;
insert into t_customer values(1,'小王',1888327654);
insert into t_customer values(2,'天天',3456546354);
insert into t_customer values(3,'阿大',123345566);
insert into t_ticket values(1,'武汉到重庆',100,1);
insert into t_ticket values(2,'北京到上海',200,1);
insert into t_ticket values(3,'深圳到广州',50,1);

use test;insert into t_customer values(1,'小王',1888327654);insert into t_customer values(2,'天天',3456546354);insert into t_customer values(3,'阿大',123345566);insert into  t_ticket values(1,'武汉到重庆',100,1);insert into  t_ticket values(2,'北京到上海',200,1);insert into  t_ticket values(3,'深圳到广州',50,1);

传统的联合查询的方法

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select c.*,t.* from t_customer c JOIN t_ticket t ON (c.customerId=t.ticketCId) where c.customerName ='小王';

select c.*,t.* from t_customer c  JOIN t_ticket t ON (c.customerId=t.ticketCId) where c.customerName ='小王';

结果如下：

二、工程创建

1、新建java工程，导入需要的包，最后整个工程目录如下：

2、创建表对应的类：

Customer.java:

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package com.mucfc.model;
import java.util.List;
/**
*顾客信息类
*@author linbingwen
*@2015年5月13日8:30:12
*/
public class Customer {
private Integer customerId;
private String customerName;
private Integer customerTel;
private List<Ticket> tickets;//使用一个List来表示车票
public List<Ticket> getTickets() {
return tickets;
}
public void setTickets(List<Ticket> tickets) {
this.tickets = tickets;
}
public Integer getCustomerId() {
return customerId;
}
public void setCustomerId(Integer customerId) {
this.customerId = customerId;
}
public String getCustomerName() {
return customerName;
}
public void setCustomerName(String customerName) {
this.customerName = customerName;
}
public Integer getCustomerTel() {
return customerTel;
}
public void setCustomerTel(Integer customerTel) {
this.customerTel = customerTel;
}
@Override
public String toString() {
return "Customer [customerId=" + customerId + ", customerName="
+ customerName + ", customerTel=" + customerTel+"]";
}
}

package com.mucfc.model;import java.util.List;/** *顾客信息类 *@author linbingwen *@2015年5月13日8:30:12 */public class Customer { private Integer customerId; private String customerName; private Integer customerTel; private List<Ticket> tickets;//使用一个List来表示车票 public List<Ticket> getTickets() {  return tickets; } public void setTickets(List<Ticket> tickets) {  this.tickets = tickets; } public Integer getCustomerId() {  return customerId; } public void setCustomerId(Integer customerId) {  this.customerId = customerId; } public String getCustomerName() {  return customerName; } public void setCustomerName(String customerName) {  this.customerName = customerName; } public Integer getCustomerTel() {  return customerTel; } public void setCustomerTel(Integer customerTel) {  this.customerTel = customerTel; } @Override public String toString() {  return "Customer [customerId=" + customerId + ", customerName="    + customerName + ", customerTel=" + customerTel+"]"; }}

Ticket.java:

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package com.mucfc.model;
/**
*车票信息类
*@author linbingwen
*@2015年5月13日8:30:12
*/
public class Ticket {
private Integer ticketId;
private String ticketAddress;
private Integer ticketPrice;
private Integer ticketCId;
private Customer customer;//使用一个customer来表示顾客
public Customer getCustomer() {
return customer;
}
public void setCustomer(Customer customer) {
this.customer = customer;
}
public Integer getTicketId() {
return ticketId;
}
public void setTicketId(Integer ticketId) {
this.ticketId = ticketId;
}
public String getTicketAddress() {
return ticketAddress;
}
public void setTicketAddress(String ticketAddress) {
this.ticketAddress = ticketAddress;
}
public Integer getTicketPrice() {
return ticketPrice;
}
public void setTicketPrice(Integer ticketPrice) {
this.ticketPrice = ticketPrice;
}
public Integer getTicketCId() {
return ticketCId;
}
public void setTicketCId(Integer ticketCId) {
this.ticketCId = ticketCId;
}
@Override
public String toString() {
return "Ticket [ticketId=" + ticketId + ", ticketAddress="
+ ticketAddress + ", ticketPrice=" + ticketPrice
+ ", ticketCId=" + ticketCId + "]";
}
}

package com.mucfc.model;/** *车票信息类 *@author linbingwen *@2015年5月13日8:30:12 */public class Ticket { private Integer ticketId; private String ticketAddress; private Integer ticketPrice; private Integer ticketCId; private Customer customer;//使用一个customer来表示顾客 public Customer getCustomer() {  return customer; } public void setCustomer(Customer customer) {  this.customer = customer; } public Integer getTicketId() {  return ticketId; } public void setTicketId(Integer ticketId) {  this.ticketId = ticketId; } public String getTicketAddress() {  return ticketAddress; } public void setTicketAddress(String ticketAddress) {  this.ticketAddress = ticketAddress; } public Integer getTicketPrice() {  return ticketPrice; } public void setTicketPrice(Integer ticketPrice) {  this.ticketPrice = ticketPrice; } public Integer getTicketCId() {  return ticketCId; } public void setTicketCId(Integer ticketCId) {  this.ticketCId = ticketCId; } @Override public String toString() {  return "Ticket [ticketId=" + ticketId + ", ticketAddress="    + ticketAddress + ", ticketPrice=" + ticketPrice    + ", ticketCId=" + ticketCId + "]"; }}

注意Customer.java:中有个list,list来存放车票，Ticket.java中有一个 customer。

3、定义sql映射文件

（1）首先是一对多关联：

MyBatis中使用collection标签来解决一对一的关联查询，collection标签可用的属性如下：

property:指的是集合属性的值
ofType:指的是集合中元素的类型
column:所对应的外键字段名称
select:使用另一个查询封装的结果

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<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mucfc.model.CustomerMapper">
<resultMap type="Customer" id="customerBean">
<id column="customerId" property="customerId"/>
<result column="customerName" property="customerName"/>
<result column="customerTel" property="customerTel"/>
<collection property="tickets" ofType="Ticket">
<id column="ticketId" property="ticketId"/>
<result column="ticketAddress" property="ticketAddress"/>
<result column="ticketPrice" property="ticketPrice"/>
<result column="ticketCId" property="ticketCId"/>
</collection>
</resultMap>
<select id="selectCustomerByName" parameterType="string" resultMap="customerBean">
select c.*,t.* from t_customer c,t_ticket t where c.customerId=t.ticketCId and c.customerName =#{customerName};
</select>
</mapper>

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.mucfc.model.CustomerMapper"> <!-- 定义数据库字段与实体对象的映射关系 --> <resultMap type="Customer" id="customerBean">  <id column="customerId" property="customerId"/>  <result column="customerName" property="customerName"/>  <result column="customerTel" property="customerTel"/>    <!-- 一对多的关系 -->  <!-- property: 指的是集合属性的值, ofType：指的是集合中元素的类型 -->  <collection property="tickets" ofType="Ticket">   <id column="ticketId" property="ticketId"/>   <result column="ticketAddress" property="ticketAddress"/>   <result column="ticketPrice" property="ticketPrice"/>   <result column="ticketCId" property="ticketCId"/>  </collection> </resultMap>   <!-- 根据id查询Person, 关联将Orders查询出来 --> <select id="selectCustomerByName" parameterType="string" resultMap="customerBean">  select c.*,t.* from t_customer c,t_ticket t  where  c.customerId=t.ticketCId and c.customerName =#{customerName}; </select>  </mapper>

（2）接着是一对一关联：

MyBatis中使用association标签来解决一对一的关联查询，association标签可用的属性如下：

property:对象属性的名称
javaType:对象属性的类型
column:所对应的外键字段名称
select:使用另一个查询封装的结果

[html] view plain copy print ?

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mucfc.model.TicketMapper">
<resultMap type="Ticket" id="ticketBean">
<id column="ticketId" property="ticketId" />
<result column="ticketAddress" property="ticketAddress" />
<result column="ticketPrice" property="ticketPrice" />
<result column="ticketCId" property="ticketCId" />
<association property="customer" javaType="Customer">
<id column="customerId" property="customerId" />
<result column="customerName" property="customerName" />
<result column="customerTel" property="customerTel" />
</association>
</resultMap>
<select id="selectTicketById" parameterType="int" resultMap="ticketBean">
select c.*,t.* from t_customer c,t_ticket t where
c.customerId=t.ticketCId and t.ticketId =#{ticketId}
</select>
</mapper>

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.mucfc.model.TicketMapper"> <!-- 定义数据库字段与实体对象的映射关系  --> <resultMap type="Ticket" id="ticketBean">  <id column="ticketId" property="ticketId" />  <result column="ticketAddress" property="ticketAddress" />  <result column="ticketPrice" property="ticketPrice" />  <result column="ticketCId" property="ticketCId" />  <!-- 一对一的关系 -->  <!-- property: 指的是属性的值, javaType：指的是元素的类型 -->  <association property="customer" javaType="Customer">   <id column="customerId" property="customerId" />   <result column="customerName" property="customerName" />   <result column="customerTel" property="customerTel" />  </association> </resultMap> <!-- 根据id查询ticket, 关联将Customer查询出来 --> <select id="selectTicketById" parameterType="int" resultMap="ticketBean">  select c.*,t.* from t_customer c,t_ticket t where  c.customerId=t.ticketCId and t.ticketId =#{ticketId} </select></mapper>

4、总配置文件

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<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<typeAliases>
<typeAlias alias="Customer" type="com.mucfc.model.Customer"/>
<typeAlias alias="Ticket" type="com.mucfc.model.Ticket" />
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="christmas258@"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/mucfc/model/CustomerMapper.xml" />
<mapper resource="com/mucfc/model/TicketMapper.xml" />
</mappers>
</configuration>

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><!-- 这是根标签  --><configuration> <!-- 设置别名  --> <typeAliases>  <typeAlias alias="Customer" type="com.mucfc.model.Customer"/>  <typeAlias alias="Ticket" type="com.mucfc.model.Ticket" /> </typeAliases>  <!-- 配置数据源相关的信息  --> <environments default="development">  <environment id="development">   <transactionManager type="JDBC" />   <dataSource type="POOLED">   <property name="driver" value="com.mysql.jdbc.Driver"/>    <property name="url" value="jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8"/>    <property name="username" value="root"/>    <property name="password" value="christmas258@"/>     </dataSource>  </environment> </environments>  <!-- 列出映射文件 --> <mappers>  <mapper resource="com/mucfc/model/CustomerMapper.xml" />  <mapper resource="com/mucfc/model/TicketMapper.xml" />  </mappers></configuration>

5、测试

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package com.mucfc.test;
import java.io.Reader;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import com.mucfc.model.Customer;
import com.mucfc.model.Ticket;
public class Test {
private static SqlSessionFactory sqlSessionFactory;
private static Reader reader;
static {
try {
reader = Resources.getResourceAsReader("mybatis-config.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (Exception e) {
e.printStackTrace();
}
}
/*
* 一对一关联查询
*/
public static void selectTicketById(int id) {
SqlSession session = null;
try {
session = sqlSessionFactory.openSession();
Ticket ticket = (Ticket) session.selectOne(
"com.mucfc.model.TicketMapper.selectTicketById", id);
if (ticket == null)
System.out.println("null");
else {
System.out.println(ticket);
System.out.println(ticket.getCustomer());
}
} finally {
session.close();
}
}
/*
* 一对多关联查询
*/
public static void selectCustomerByName(String string) {
SqlSession session = null;
try {
session = sqlSessionFactory.openSession();
Customer customer = (Customer) session
.selectOne(
"com.mucfc.model.CustomerMapper.selectCustomerByName",
string);
if (customer == null)
System.out.println("null");
else {
System.out.println(customer);
List<Ticket> tickets = customer.getTickets();
for (Ticket ticket : tickets) {
System.out.println(ticket);
}
}
} finally {
session.close();
}
}
public static void main(String[] args) {
System.out.println("==============一对一查询，根据车票来查顾客===============");
selectTicketById(1);
System.out.println("==============多对一查询，根据顾客来查车票===============");
selectCustomerByName("小王");
}
}

package com.mucfc.test;import java.io.Reader;import java.util.List;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.mucfc.model.Customer;import com.mucfc.model.Ticket;public class Test { private static SqlSessionFactory sqlSessionFactory; private static Reader reader; static {  try {   reader = Resources.getResourceAsReader("mybatis-config.xml");   sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);  } catch (Exception e) {   e.printStackTrace();  } } /*  * 一对一关联查询  */ public static void selectTicketById(int id) {  SqlSession session = null;  try {   session = sqlSessionFactory.openSession();   Ticket ticket = (Ticket) session.selectOne(     "com.mucfc.model.TicketMapper.selectTicketById", id);   if (ticket == null)    System.out.println("null");   else {    System.out.println(ticket);    System.out.println(ticket.getCustomer());   }  } finally {   session.close();  } } /*  * 一对多关联查询  */ public static void selectCustomerByName(String string) {  SqlSession session = null;  try {   session = sqlSessionFactory.openSession();   Customer customer = (Customer) session     .selectOne(       "com.mucfc.model.CustomerMapper.selectCustomerByName",       string);   if (customer == null)    System.out.println("null");   else {    System.out.println(customer);    List<Ticket> tickets = customer.getTickets();    for (Ticket ticket : tickets) {     System.out.println(ticket);    }   }  } finally {   session.close();  } } public static void main(String[] args) {  System.out.println("==============一对一查询，根据车票来查顾客===============");  selectTicketById(1);  System.out.println("==============多对一查询，根据顾客来查车票===============");  selectCustomerByName("小王"); }}

结果：

结果显示，查询正确。

三、ResultMap标签　　　　　　　　　　　　　　　　　　　　　　　　

MyBatis中在查询进行select映射的时候，返回类型可以用resultType，也可以用resultMap，resultType是直接表示返回类型的，而resultMap则是对外部ResultMap的引用，但是resultType跟resultMap不能同时存在。在MyBatis进行查询映射的时候，其实查询出来的每一个属性都是放在一个对应的Map里面的，其中键是属性名，值则是其对应的值。当提供的返回类型属性是resultType的时候，MyBatis会将Map里面的键值对取出赋给resultType所指定的对象对应的属性。所以其实MyBatis的每一个查询映射的返回类型都是ResultMap，只是当我们提供的返回类型属性是resultType的时候，MyBatis对自动的给我们把对应的值赋给resultType所指定对象的属性，而当我们提供的返回类型是resultMap的时候，因为Map不能很好表示领域模型，我们就需要自己再进一步的把它转化为对应的对象，这常常在复杂查询中很有作用。

当Java接口与XML文件在一个相对路径下时，可以不在myBatis配置文件的mappers中声明:

[html] view plain copy print ?

<mappers>
<mapper resource="com/mucfc/model/CustomerMapper.xml" />
<mapper resource="com/mucfc/model/TicketMapper.xml" />
</mappers>

 <!-- 列出映射文件 --> <mappers>  <mapper resource="com/mucfc/model/CustomerMapper.xml" />  <mapper resource="com/mucfc/model/TicketMapper.xml" />  </mappers>

SQL 映射XML 文件一些初级的元素：

[sql] view plain copy print ?

1. cache – 配置给定模式的缓存
2. cache-ref – 从别的模式中引用一个缓存
3. resultMap – 这是最复杂而却强大的一个元素了，它描述如何从结果集中加载对象
4. sql – 一个可以被其他语句复用的SQL 块
5. insert – 映射INSERT 语句
6. update – 映射UPDATE 语句
7. delete – 映射DELEETE 语句
8. select - 映射SELECT语句

1. cache – 配置给定模式的缓存2. cache-ref – 从别的模式中引用一个缓存3. resultMap – 这是最复杂而却强大的一个元素了，它描述如何从结果集中加载对象4. sql – 一个可以被其他语句复用的SQL 块5. insert – 映射INSERT 语句6. update – 映射UPDATE 语句7. delete – 映射DELEETE 语句8. select - 映射SELECT语句

resultMap 是MyBatis 中最重要最强大的元素了。你可以让你比使用JDBC 调用结果集省掉90%的代码，也可以让你做许多JDBC 不支持的事。现实上，要写一个等同类似于交互的映射这样的复杂语句，可能要上千行的代码。ResultMaps 的目的，就是这样简单的语句而不需要多余的结果映射，更多复杂的语句，除了只要一些绝对必须的语句描述关系以外，再也不需要其它的。
resultMap属性：type为java实体类；id为此resultMap的标识。
resultMap可以设置的映射：

[sql] view plain copy print ?

1. constructor – 用来将结果反射给一个实例化好的类的构造器
a) idArg – ID 参数；将结果集标记为ID，以方便全局调用
b) arg –反射到构造器的通常结果
2. id – ID 结果，将结果集标记为ID，以方便全局调用
3. result – 反射到JavaBean 属性的普通结果
4. association – 复杂类型的结合；多个结果合成的类型
a) nested result mappings – 几resultMap 自身嵌套关联，也可以引用到一个其它上
5. collection –复杂类型集合a collection of complex types
6. nested result mappings – resultMap 的集合，也可以引用到一个其它上
7. discriminator – 使用一个结果值以决定使用哪个resultMap
a) case – 基本一些值的结果映射的case 情形
i. nested result mappings –一个case 情形本身就是一个结果映射，因此也可以包括一些相同的元素，也可以引用一个外部resultMap。

1. constructor – 用来将结果反射给一个实例化好的类的构造器a) idArg – ID 参数；将结果集标记为ID，以方便全局调用b) arg –反射到构造器的通常结果2. id – ID 结果，将结果集标记为ID，以方便全局调用3. result – 反射到JavaBean 属性的普通结果4. association – 复杂类型的结合；多个结果合成的类型a) nested result mappings – 几resultMap 自身嵌套关联，也可以引用到一个其它上5. collection –复杂类型集合a collection of complex types6. nested result mappings – resultMap 的集合，也可以引用到一个其它上7. discriminator – 使用一个结果值以决定使用哪个resultMapa) case – 基本一些值的结果映射的case 情形i. nested result mappings –一个case 情形本身就是一个结果映射，因此也可以包括一些相同的元素，也可以引用一个外部resultMap。

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22 SSM框架-Mybatis关联查询一对一和一对多的实现（4）

一、创建表、分析

二、工程创建

三、ResultMap标签

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