1、一對一關聯查詢的案例
(1)需求
根據班級id查詢班級資訊(帶老師資訊)
(2)建立表和資料
建立一張教師表和班級表,這裡我們假設一個老師隻負責教一個班,那麼老師和班級之間的關系就是一種一對一的關系。
CREATE TABLE teacher(
t_id INT PRIMARY KEY AUTO_INCREMENT,
t_name VARCHAR(20)
);
CREATE TABLE class(
c_id INT PRIMARY KEY AUTO_INCREMENT,
c_name VARCHAR(20),
teacher_id INT
);
ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id);
INSERT INTO teacher(t_name) VALUES('teacher1');
INSERT INTO teacher(t_name) VALUES('teacher2');
INSERT INTO class(c_name, teacher_id) VALUES('class_a', 1);
INSERT INTO class(c_name, teacher_id) VALUES('class_b', 2);
(3)建構實體
老師:
public class Teacher {
// 定義實體類的屬性,與teacher表中的字段對應
private int id; // id===>t_id
private String name; // name===>t_name
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Teacher [id=" + id + ", name=" + name + "]";
}
}
班級:
public class Classes {
// 定義實體類的屬性,與class表中的字段對應
private int id; // id===>c_id
private String name; // name===>c_name
/**
* class表中有一個teacher_id字段,是以在Classes類中定義一個teacher屬性,
* 用于維護teacher和class之間的一對一關系,通過這個teacher屬性就可以知道這個班級是由哪個老師負責的
*/
private Teacher teacher;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
@Override
public String toString() {
return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher
+ "]";
}
}
(4)定義Mapper對象
public interface ClassMapper {
/**
* 用于測試,非懶加載的one2one的實作
*
* @param id
* @return
*/
public Classes getClass1(int id);
/**
* 用于測試,懶加載的one2one的實作
*
* @param id
* @return
*/
public Classes getClass2(int id);
}
(5)定義sql映射檔案classMapper.xml
<?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.baowei.mapper.ClassMapper">
<!--
根據班級id查詢班級資訊(帶老師的資訊)
##1. 聯表查詢(非懶加載的實作)
SELECT * FROM class c,teacher t WHERE c.teacher_id=t.t_id AND c.c_id=1;
##2. 執行兩次查詢(懶加載的實作)
SELECT * FROM class WHERE c_id=1; //teacher_id=1
SELECT * FROM teacher WHERE t_id=1;//使用上面得到的teacher_id
-->
<!--
方式一:(非懶加載的實作)
嵌套結果:使用嵌套結果映射來處理重複的聯合結果的子集
封裝聯表查詢的資料(去除重複的資料)
select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=1
-->
<select id="getClass1" parameterType="int" resultMap="ClassResultMap">
select *
from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
</select>
<!-- 使用resultMap映射實體類和字段之間的一一對應關系 -->
<resultMap type="com.baowei.entity.Classes" id="ClassResultMap">
<id property="id" column="c_id" />
<result property="name" column="c_name" />
<association property="teacher" javaType="com.baowei.entity.Teacher">
<id property="id" column="t_id" />
<result property="name" column="t_name" />
</association>
</resultMap>
<!--
方式二:(懶加載的實作)
嵌套查詢:通過執行另外一個SQL映射語句來傳回預期的複雜類型
SELECT * FROM class WHERE c_id=1;
SELECT * FROM teacher WHERE t_id=1 //1 是上一個查詢得到的teacher_id的值
-->
<select id="getClass2" parameterType="int" resultMap="ClassResultMap2">
select *
from class where c_id=#{id}
</select>
<!-- 使用resultMap映射實體類和字段之間的一一對應關系 -->
<resultMap type="com.baowei.entity.Classes" id="ClassResultMap2">
<id property="id" column="c_id" />
<result property="name" column="c_name" />
<association property="teacher" column="teacher_id"
select="getTeacher" />
</resultMap>
<select id="getTeacher" parameterType="int"
resultType="com.baowei.entity.Teacher">
SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>
</mapper>
(6)SqlMapConfig.xml配置
<?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>
<!--用于加載資料庫的連接配接配置 -->
<properties resource="db.properties" />
<!--用于設定懶加載的設定 -->
<settings>
<!-- 打開延遲加載的開關 -->
<setting name="lazyLoadingEnabled" value="true" />
<!-- 将積極加載改為消息加載即按需加載 -->
<setting name="aggressiveLazyLoading" value="false" />
</settings>
<!--資料庫的連接配接配置 -->
<environments default="development">
<environment id="development">
<!-- 使用jdbc事務管理,事務控制由mybatis -->
<transactionManager type="JDBC" />
<!-- 資料庫連接配接池,由mybatis管理 -->
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}" />
<property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.username}" />
<property name="password" value="${jdbc.password}" />
</dataSource>
</environment>
</environments>
<!-- 加載 映射檔案 -->
<mappers>
<package name="com.baowei.mapper" />
</mappers>
</configuration>
(7).MyBatisUtil.java工具
import java.io.IOException;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MyBatisUtil {
/**
* 擷取SqlSessionFactory
*
* @return SqlSessionFactory
*/
public static SqlSessionFactory getSqlSessionFactory() {
String resource = "SqlMapConfig.xml";
InputStream inputStream = null;
SqlSessionFactory sqlSessionFactory = null;
try {
inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder()
.build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
return sqlSessionFactory;
}
/**
* 擷取SqlSession
*
* @return SqlSession
*/
public static SqlSession getSqlSession() {
return getSqlSessionFactory().openSession();
}
/**
* 擷取SqlSession
*
* @param isAutoCommit
* true 表示建立的SqlSession對象在執行完SQL之後會自動送出事務 false
* 表示建立的SqlSession對象在執行完SQL之後不會自動送出事務
* ,這時就需要我們手動調用sqlSession.commit()送出事務
* @return SqlSession
*/
public static SqlSession getSqlSession(boolean isAutoCommit) {
return getSqlSessionFactory().openSession(isAutoCommit);
}
public static void main(String[] args) {
System.out.println(getSqlSessionFactory());
}
}
(8)測試代碼
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import com.baowei.entity.Classes;
import com.baowei.mapper.ClassMapper;
import com.baowei.utils.MyBatisUtil;
public class TestOne2One {
/**
* 非懶加載的one2one的測試
*/
@Test
public void testGetClass() {
SqlSession sqlSession = MyBatisUtil.getSqlSession();
ClassMapper mapper = sqlSession.getMapper(ClassMapper.class);
Classes clazz = mapper.getClass1(1);
// 使用SqlSession執行完SQL之後需要關閉SqlSession
sqlSession.close();
System.out.println(clazz.getId());
}
/**
* 懶加載的one2one的測試
*/
@Test
public void testGetClass2() {
SqlSession sqlSession = MyBatisUtil.getSqlSession();
ClassMapper mapper = sqlSession.getMapper(ClassMapper.class);
Classes clazz = mapper.getClass2(1);
// 使用SqlSession執行完SQL之後需要關閉SqlSession
sqlSession.close();
System.out.println(clazz.getId());
// 可用于測試懶加載(檢視日志的sql輸出結果,就可以發現使用了懶加載)
//System.out.println(clazz.getTeacher());
}
}
2.一對多/多對一查詢案例
(1)需求
本執行個體使用顧客和訂單的例子做說明: 一個顧客可以有多個訂單, 一個訂單隻對應一個顧客。
(2)建立表和資料
CREATE DATABASE test;
USE test;
CREATE TABLE person(
personId VARCHAR(36) PRIMARY KEY,
personName VARCHAR(64),
personAddress VARCHAR(128),
personTel VARCHAR(11)
);
CREATE TABLE orders(
orderId VARCHAR(36) PRIMARY KEY,
orderNumber VARCHAR(20),
orderPrice INT,
pid VARCHAR(36)
);
INSERT INTO person VALUES('001', 'Jack', 'Wuhan', '1234567');
INSERT INTO orders VALUES('O_00001', '00001', 100, '001');
INSERT INTO orders VALUES('O_00002', '00002', 200, '001');
SELECT p.*, o.*
FROM person p
JOIN orders o ON (p.personId=o.pid)
WHERE p.personId = '001'
(3)建構實體
客戶:
public class Person {
private String id;
private String name;
private String address;
private String tel;
private List<Order> orders;
@Override
public String toString() {
return "{id: " + id + ", name: " + name + ", address: " + address + ", tel: " + tel + "}";
}
}
訂單:
public class Order {
private String id;
private String number;
private int price;
private Person person;
@Override
public String toString() {
return "{id: " + id + ", number: " + number + ", price: " + price + "}";
}
}
(4)一對多實體配置: Person.xml
<?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.zdp.domain.Person">
<resultMap type="Person" id="personBean">
<id column="personId" property="id"/>
<result column="personName" property="name"/>
<result column="personAddress" property="address"/>
<result column="personTel" property="tel"/>
<!-- 一對多的關系 -->
<!-- property: 指的是集合屬性的值, ofType:指的是集合中元素的類型 -->
<collection property="orders" ofType="Order">
<id column="orderId" property="id"/>
<result column="orderNumber" property="number"/>
<result column="orderPrice" property="price"/>
</collection>
</resultMap>
<!-- 根據id查詢Person, 關聯将Orders查詢出來 -->
<select id="selectPersonById" parameterType="string" resultMap="personBean">
select p.*, o.* from person p, orders o where p.personId = o.pid and p.personId = #{id}
</select>
</mapper>
(5)多對一實體配置:order.xml
<?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.zdp.domain.Order">
<resultMap type="Order" id="orderBean">
<id column="orderId" property="id"/>
<result column="orderNumber" property="number"/>
<result column="orderPrice" property="price"/>
<!-- 多對一的關系 -->
<!-- property: 指的是屬性的值, javaType:指的是屬性的類型-->
<association property="person" javaType="Person">
<id column="personId" property="id"/>
<result column="personName" property="name"/>
<result column="personAddress" property="address"/>
<result column="personTel" property="tel"/>
</association>
</resultMap>
<!-- 根據id查詢Order, 關聯将Person查詢出來 -->
<select id="selectOrderById" parameterType="string" resultMap="orderBean">
select p.*, o.* from person p, orders o where p.personId = o.pid and o.orderId = #{id}
</select>
</mapper>
(6)SqlMapConfig.xml配置
<?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 type="com.zdp.domain.Person" alias="Person"/>
<typeAlias type="com.zdp.domain.Order" alias="Order"/>
</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/test" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
<mappers>
<!-- 映射檔案的位置 -->
<mapper resource="com/zdp/domain/Person.xml" />
<mapper resource="com/zdp/domain/Order.xml" />
</mappers>
</configuration>
(7)測試代碼
/**
* 測試一對多和多對一
*/
public class MybatisTest {
private SqlSessionFactory ssf;
@Before
public void initSF() throws Exception {
String resource = "sqlMapConfig.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
ssf = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test//一對多關聯查詢
public void selectPersonById()throws Exception{
SqlSession session = ssf.openSession();
Person person = session.selectOne("com.zdp.domain.Person.selectPersonById", "001");
System.out.println(person.getOrders());
}
@Test//多對一關聯查詢
public void selectOrderById()throws Exception{
SqlSession session = ssf.openSession();
Order order = session.selectOne("com.zdp.domain.Order.selectOrderById", "O_00001");
System.out.println(order.getPerson().getName());
}
}
3.參考博文
(1)http://www.cnblogs.com/xdp-gacl/p/4264440.html
(2)http://blog.csdn.net/jkxiaoxing/article/details/52199386