Java MyBatis高级玩法

2.2.parameterType(输入类型)

2.2.1.传递简单类型

使用#{}占位符，或者${}进行sql拼接。

2.2.2.传递pojo对象

Mybatis使用ognl表达式解析对象字段的值，#{}或者${}括号中的值为pojo属性名称。

2.2.3.传递pojo包装对象

开发中通过可以使用pojo传递查询条件。

查询条件可能是综合的查询条件，不仅包括用户查询条件还包括其它的查询条件（比如查询用户信息的时候，将用户购买商品信息也作为查询条件），这时可以使用包装对象传递输入参数。
包装对象：Pojo类中的一个属性是另外一个pojo。

需求：根据用户名模糊查询用户信息，查询条件放到QueryVo的user属性中。

2.2.3.1.编写QueryVo

package cn.zdfy.mapper;

import cn.zdfy.User;

public class QueryVo {
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

}

2.2.3.2.Sql语句

SELECT * FROM user WHERE username LIKE ‘%张%’
在UserMapper.xml中配置sql，如下:

<mapper namespace="cn.zdfy.mapper.UserMapper">
    <select id="queryUserByQueryVo" parameterType="queryVo"
        resultType="user">
        select * from user where username like '%${user.username}%'
    select>
mapper>

2.2.3.4.Mapper接口

/**
 * 根据包类查询用户
 * 
 * @param qv
 * @return
 */
List queryUserByQueryVo(QueryVo qv);

2.2.3.5.测试方法

@Test
public void fun3() {
    // 获取sqlSession，和spring整合后由spring管理
    SqlSession sqlSession = sqlSessionFactory.openSession();
    // 从sqlSession中获取Mapper接口的代理对象
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    QueryVo qv = new QueryVo();
    User u = new User();
    u.setUsername("张");
    qv.setUser(u);
    List list = userMapper.queryUserByQueryVo(qv);
    for(User user:list) {
        System.out.println(user);
    }
    sqlSession.close();
}

2.3.resultType(输出类型)

2.3.1.输出简单类型

需求:查询用户表数据条数
sql：SELECT count(*) FROM user

2.3.1.1.Mapper.xml文件

    <select id="queryUserCount" resultType="int">
        select count(*) from user
    select>

2.3.1.2.Mapper接口

在UserMapper添加方法，如下

/**
 * 查询用户数据条数
 * 
 * @return
 */
int queryUserCount();

2.3.1.3测试方法

@Test
public void fun4() {
    SqlSession openSession = sqlSessionFactory.openSession();
    UserMapper mapper = openSession.getMapper(UserMapper.class);
    int queryUserCount = mapper.queryUserCount();
    System.out.println(queryUserCount);
    openSession.close();
}

2.3.2.输出pojo对象

2.3.3.输出pojo列表

2.4.resultMap

resultType可以指定将查询结果映射为pojo，但需要pojo的属性名和sql查询的列名一致方可映射成功。
如果sql查询字段名和pojo的属性名不一致，可以通过resultMap将字段名和属性名作一个对应关系 ，resultMap实质上还需要将查询结果映射到pojo对象中。
resultMap可以实现将查询结果映射为复杂类型的pojo，比如在查询结果映射对象中包括pojo和list实现一对一查询和一对多查询。

需求：查询订单表order的所有数据
sql：SELECT id, user_id, number, createtime, note FROM order

2.4.1.声明pojo对象

package cn.zdfy;

import java.util.Date;

public class Order {
    private int id;
    private Integer userId;
    private String number;
    private Date createtime;
    private String note;

    public int getId() {
        return id;
    }

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

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Date getCreatetime() {
        return createtime;
    }

    public void setCreatetime(Date createtime) {
        this.createtime = createtime;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }
}

2.4.2.Mapper.xml文件

创建OrderMapper.xml配置文件，如下：

<mapper namespace="cn.zdfy.mapper.OrderMapper">
    <select id="queryOrderAll" resultType="order">
        select id, user_id, number, createtime, note from orders
    select>
mapper>

2.4.3.Mapper接口

package cn.zdfy.mapper;

import java.util.List;

import cn.zdfy.Order;

public interface OrderMapper {
    /**
     * 查询所有订单
     * 
     * @return
     */
    List queryOrderAll();
}

2.4.4.测试方法

package cn.zdfy;

import java.io.IOException;
import java.io.InputStream;
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 org.junit.Before;
import org.junit.Test;

import cn.zdfy.mapper.OrderMapper;

public class OrderMapperTest {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void init() throws IOException {
        InputStream is = Resources.getResourceAsStream("SqlMapConfig.xml");
        this.sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
    }

    @Test
    public void testQueryAll() {
        SqlSession sqlSession = this.sqlSessionFactory.openSession();
        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        List queryOrderAll = mapper.queryOrderAll();
        for (Order o : queryOrderAll) {
            System.out.println("o===============" + o);
        }
        sqlSession.close();

    }
}

2.4.5.效果

DEBUG [main] - <==      Total: 3
o===============Order [id=3, userId=null, number=1000010, createtime=Wed Feb 04 13:22:35 CST 2015, note=null]
o===============Order [id=4, userId=null, number=1000011, createtime=Tue Feb 03 13:22:41 CST 2015, note=null]
o===============Order [id=5, userId=null, number=1000012, createtime=Thu Feb 12 16:13:23 CST 2015, note=null]
DEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@7a765367]
DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@7a765367]
DEBUG [main] - Returned connection 2054574951 to pool.

发现userId为null
解决方案：使用resultMap

2.4.6.使用resultMap

由于上边的mapper.xml中sql查询列(user_id)和Order类属性(userId)不一致，所以查询结果不能映射到pojo中。
需要定义resultMap，把orderResultMap将sql查询列(user_id)和Order类属性(userId)对应起来

改造OrderMapper.xml，如下：

<mapper namespace="cn.zdfy.mapper.OrderMapper">
    
    
    <resultMap type="order" id="orderResultMap">
        
        
        
        <id property="id" column="id" />
        
        <result property="userId" column="user_id" />
        <result property="number" column="number" />
        <result property="createtime" column="createtime" />
        <result property="note" column="note" />
    resultMap>
    <select id="queryOrderAll" resultMap="orderResultMap">
        select id, user_id,
        number, createtime, note from orders
    select>
mapper>

2.4.7.效果

只需要修改Mapper.xml就可以了，再次测试结果如下

DEBUG [main] - <==      Total: 3
o===============Order [id=3, userId=1, number=1000010, createtime=Wed Feb 04 13:22:35 CST 2015, note=null]
o===============Order [id=4, userId=1, number=1000011, createtime=Tue Feb 03 13:22:41 CST 2015, note=null]
o===============Order [id=5, userId=10, number=1000012, createtime=Thu Feb 12 16:13:23 CS

3.动态sql

通过mybatis提供的各种标签方法实现动态拼接sql。
需求：根据性别和名字查询用户
查询sql：
SELECT id, username, birthday, sex, address FROM user WHERE sex = 1 AND username LIKE ‘%张%’

3.1.If标签

3.1.1.Mapper.xml文件

UserMapper.xml配置sql，如下：

<select id="queryUserByWhere" parameterType="user" resultType="user">
    select id, username, birthday, sex, address from user where
    sex = #{sex} and username like '%${username}%'
select>

3.1.2.Mapper接口

编写Mapper接口，如下：

/**
 * 根据条件查询用户
 * 
 * @param user
 * @return
 */
List queryUserByWhere(User user);

3.1.3.测试方法

@Test
public void testQueryByWhere() {
    SqlSession sqlSession = sqlSessionFactory.openSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User u = new User();
    u.setSex("1");
    u.setUsername("张");
    List list = mapper.queryUserByWhere(u);
    for (User user : list) {
        System.out.println("===== " + user);
    }
    sqlSession.close();
}

3.1.4.效果

DEBUG [main] - <==      Total: 3
===== User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
===== User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]
===== User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州]

注释掉 u.setSex(“1”)，测试结果如下

DEBUG [main] - ==>  Preparing: select id, username, birthday, sex, address from user where sex = ? and username like '%张%' 
DEBUG [main] - ==> Parameters: null
DEBUG [main] - <==      Total: 0

测试结果二很显然不合理。
按照之前所学的，要解决这个问题，需要编写多个sql，查询条件越多，需要编写的sql就更多了，显然这样是不靠谱的。
解决方案，使用动态sql的if标签

3.1.5.使用if标签

改造UserMapper.xml，如下：

<select id="queryUserByWhere" parameterType="user" resultType="user">
    select id, username, birthday, sex, address from user where
    1=1
    <if test=" sex!=null and sex !='' ">if>
    <if test="username != null and username != ''">
        and username like
        '%${username}%'
    if>
select>

注意字符串类型的数据需要要做不等于空字符串校验。

3.1.6.效果

DEBUG [main] - <==      Total: 3
===== User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
===== User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]
===== User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州]

3.2.Where标签

上面的sql还有where 1=1 这样的语句，很麻烦
可以使用where标签进行改造

改造UserMapper.xml，如下

<select id="queryUserByWhere" parameterType="user" resultType="user">
    select id, username, birthday, sex, address from user
    
    <where>
        <if test=" sex!=null and sex !='' ">if>
        <if test="username != null and username != ''">
            and username like
            '%${username}%'
        if>
    where>
select>

3.2.1.效果

测试效果如下

DEBUG [main] - <==      Total: 3
===== User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
===== User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]
===== User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州]

3.3.Sql片段

Sql中可将重复的sql提取出来，使用时用include引用即可，最终达到sql重用的目的。
把上面例子中的id, username, birthday, sex, address提取出来，作为sql片段，如下

<select id="queryUserByWhere" parameterType="user" resultType="user">
    select
    <include refid="userFields" />
    from user
    
    <where>
        <if test=" sex!=null and sex !='' ">if>
        <if test="username != null and username != ''">
            and username like
            '%${username}%'
        if>
    where>
select>

<sql id="userFields">
    id, username, birthday, sex, address
sql>

如果要使用别的Mapper.xml配置的sql片段，可以在refid前面加上对应的Mapper.xml的namespace

3.4.foreach标签

向sql传递数组或List，mybatis使用foreach解析，如下：
根据多个id查询用户信息
查询sql：
SELECT * FROM user WHERE id IN (1,10,24)

3.4.1.改造QueryVo

如下 在pojo中定义list属性ids存储多个用户id，并添加getter/setter方法

package cn.zdfy.mapper;

import java.util.List;

import cn.zdfy.User;

public class QueryVo {
    private User user;
    private List ids;

    public List getIds() {
        return ids;
    }

    public void setIds(List ids) {
        this.ids = ids;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

}

3.4.2.Mapper.xml文件

UserMapper.xml添加sql，如下：

<select id="queryUserByIds" parameterType="queryVo" resultType="user">
    select * from user
    <where>
        
        
        
        
        
        
        <foreach collection="ids" item="item" open="id in (" close=")"
            separator=",">
            #{item}
        foreach>
    where>
select>

测试方法如下:

@Test
    public void testQueryUserByIds() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        QueryVo qv = new QueryVo();
        List ids = new ArrayList<>();
        ids.add(1);
        ids.add(10);
        ids.add(16);
        qv.setIds(ids);
        List list = mapper.queryUserByIds(qv);
        for (User u : list) {
            System.out.println("uuuu==========" + u);
        }
        // mybatis和spring整合，整合之后，交给spring管理
        sqlSession.close();
    }

测试结果

DEBUG [main] - <==      Total: 3
uuuu==========User [id=1, username=王五, sex=2, birthday=null, address=null]
uuuu==========User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
uuuu==========User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]

4.关联查询

4.1.商品订单数据模型

4.2.一对一查询

需求：查询所有订单信息，关联查询下单用户信息。

注意：因为一个订单信息只会是一个人下的订单，所以从查询订单信息出发关联查询用户信息为一对一查询。如果从用户信息出发查询用户下的订单信息则为一对多查询，因为一个用户可以下多个订单。
sql语句：

SELECT
    o.id,
    o.user_id userId,
    o.number,
    o.createtime,
    o.note,
    u.username,
    u.address
FROM
    `order` o
LEFT JOIN `user` u ON o.user_id = u.id

4.2.1.方法一：使用resultType

使用resultType，改造订单pojo类，此pojo类中包括了订单信息和用户信息
这样返回对象的时候，mybatis自动把用户信息也注入进来了

4.2.1.1.改造pojo类

OrderUser类继承Order类后OrderUser类包括了Order类的所有字段，只需要定义用户的信息字段即可，如下：

package cn.zdfy;

public class OrderUser extends Order {
    private String username;
    private String address;
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    @Override
    public String toString() {
        return "OrderUser [username=" + username + ", address=" + address + "]";
    }

}

4.2.1.2.Mapper.xml

在UserMapper.xml添加sql，如下

"queryOrderUser" resultType="orderUser">
        select 
        o.id,
        o.user_id,
        o.number,
        o.createtime,
        o.note,
        u.username,
        u.address
        from orders o  
        left join user u on o.user_id = u.id
    

4.2.1.3.Mapper接口

在UserMapper接口添加方法，如下：

/**
 * 一对一关联,查询订单同时包含用户信息
 * 
 * @return
 */
List queryOrderUser();

4.2.1.4.测试方法

@Test
public void testQueryOrderUser() {
    SqlSession sqlSession = sqlSessionFactory.openSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List list = mapper.queryOrderUser();
    for (OrderUser ou : list) {
        System.out.println(ou);
    }
    sqlSession.close();
}

4.2.1.5.效果

DEBUG [main] - <==      Total: 3
Order [id=3, userId=null, number=1000010, createtime=Wed Feb 04 13:22:35 CST 2015, note=null]
Order [id=4, userId=null, number=1000011, createtime=Tue Feb 03 13:22:41 CST 2015, note=null]
Order [id=5, userId=null, number=1000012, createtime=Thu Feb 12 16:13:23 CST 2015, note=null]

4.2.1.6.小结

定义专门的pojo类作为输出类型，其中定义了sql查询结果集所有的字段。此方法较为简单，企业中使用普遍。

4.2.2.方法二：使用resultMap

使用resultMap，定义专门的resultMap用于映射一对一查询结果。

4.2.2.1.改造pojo类

在Order类中加入User属性，user属性中用于存储关联查询的用户信息，因为订单关联查询用户是一对一关系，所以这里使用单个User对象存储关联查询的用户信息。
改造Order如下

package cn.zdfy;

import java.util.Date;

public class Order {
    private int id;
    private Integer userId;
    private String number;
    private Date createtime;
    private String note;
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public int getId() {
        return id;
    }

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

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Date getCreatetime() {
        return createtime;
    }

    public void setCreatetime(Date createtime) {
        this.createtime = createtime;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }

    @Override
    public String toString() {
        return "Order [id=" + id + ", userId=" + userId + ", number=" + number + ", createtime=" + createtime
                + ", note=" + note + ", user=" + user + "]";
    }

}

4.2.2.2.Mapper.xml

这里resultMap指定orderUserResultMap，如下：

<resultMap type="order" id="orderUserResultMap">
    <id property="id" column="id">id>
    <result property="userId" column="user_id">result>
    <result property="number" column="number">result>
    <result property="createtime" column="createtime">result>
    <result property="note" column="note">result>
    
    
    
    <association property="user" javaType="user">
        
        <id property="id" column="user_id" />
        <result property="username" column="username" />
        <result property="address" column="address" />
    association>
resultMap>

<select id="queryOrderUserResultMap" resultMap="orderUserResultMap">
    select
    o.id,
    o.user_id,
    o.number,
    o.createtime,
    o.note,
    u.username,
    u.address
    from orders
    o
    left join
    user u on o.user_id = u.id
select>

4.2.2.3.Mapper接口

/**
 * 一对一关联,查询订单,订单内部包含user属性
 * 
 * @return
 */
List queryOrderUserResultMap();

4.2.2.4.测试方法

@Test
    public void testQueryOrderUserResultMap() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List list = mapper.queryOrderUserResultMap();
        for (Order o : list) {
            System.out.println(o);
        }
        sqlSession.close();
    }

4.2.2.5.效果

DEBUG [main] - <==      Total: 3
Order [id=3, userId=1, number=1000010, createtime=Wed Feb 04 13:22:35 CST 2015, note=null, user=User [id=1, username=王五, sex=null, birthday=null, address=null]]
Order [id=4, userId=1, number=1000011, createtime=Tue Feb 03 13:22:41 CST 2015, note=null, user=User [id=1, username=王五, sex=null, birthday=null, address=null]]
Order [id=5, userId=10, number=1000012, createtime=Thu Feb 12 16:13:23 CST 2015, note=null, user=User [id=10, username=张三, sex=null, birthday=null, address=北京市]]

4.3.一对多查询

案例：查询所有用户信息及用户关联的订单信息。
用户信息和订单信息为一对多关系。
sql语句：

SELECT
    u.id,
    u.username,
    u.birthday,
    u.sex,
    u.address,
    o.id oid,
    o.number,
    o.createtime,
    o.note
FROM
    `user` u
LEFT JOIN `order` o ON u.id = o.user_id

4.3.1.修改pojo类

在User类中加入List orders属性,如下

private List<Order> orders;

4.3.2.Mapper.xml

在UserMapper.xml添加sql，如下：

<resultMap type="user" id="userOrderResultMap">
    <id property="id" column="id">id>
    <result property="username" column="username" />
    <result property="birthday" column="birthday" />
    <result property="sex" column="sex" />
    <result property="address" column="address" />

    
    <collection property="orders" javaType="list" ofType="order">
        
        <id property="id" column="oid" />
        <result property="number" column="number" />
        <result property="createtime" column="createtime" />
        <result property="note" column="note" />
    collection>
resultMap>

<select id="queryUserOrder" resultMap="userOrderResultMap">
    select
    u.id,
    u.username,
    u.birthday,
    u.sex,
    u.address,
    o.number,
    o.createtime,
    o.note
    from
    user u
    left join orders o on u.id=o.user_id
select>

4.3.3.Mapper接口

编写UserMapper接口，如下:

/**
 * 一对多关联,查询用户,用户内部包含该用户的所有订单
 * 
 * @return
 */
List queryUserOrder();

4.3.4.测试方法

@Test
public void testQueryUserOrder() {
    SqlSession sqlSession = sqlSessionFactory.openSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List list = mapper.queryUserOrder();
    for (User u : list) {
        System.out.println(u);
    }
    sqlSession.close();
}

4.3.5.效果

DEBUG [main] - <==      Total: 8
User [id=1, username=王五, sex=2, birthday=null, address=null, orders=[Order [id=0, userId=null, number=1000010, createtime=Wed Feb 04 13:22:35 CST 2015, note=null, user=null], Order [id=0, userId=null, number=1000011, createtime=Tue Feb 03 13:22:41 CST 2015, note=null, user=null]]]
User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市, orders=[Order [id=0, userId=null, number=1000012, createtime=Thu Feb 12 16:13:23 CST 2015, note=null, user=null]]]
User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州, orders=[]]
User [id=22, username=陈小明, sex=1, birthday=null, address=河南郑州, orders=[]]
User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州, orders=[]]
User [id=25, username=陈小明, sex=1, birthday=null, address=河南郑州, orders=[]]
User [id=26, username=王五, sex=null, birthday=null, address=null, orders=[]]

5.Mybatis整合spring

5.1.整合思路

1、SqlSessionFactory对象应该放到spring容器中作为单例存在。
2、传统dao的开发方式中，应该从spring容器中获得sqlsession对象。
3、Mapper代理形式中，应该从spring容器中直接获得mapper的代理对象。
4、数据库的连接以及数据库连接池事务管理都交给spring容器来完成。

5.2.整合需要的jar包

1、spring的jar包
2、Mybatis的jar包
3、Spring+mybatis的整合包。
4、Mysql的数据库驱动jar包。
5、数据库连接池的jar包。
jar包位置如下所示：