MyBatis中动态sql语句---if、where、foreach、sql等标签的使用

数据库表

在IDEA中创建maven项目

整体架构

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.uek</groupId>
    <artifactId>mybatis03-study02-mybatisSQL</artifactId>
    <version>1.0-SNAPSHOT</version>

    <!--打包方式-->
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.6</version>
        </dependency>

        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.12</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
        </dependency>
    </dependencies>

</project>

MyBatis的主配置文件

在resource目录下------SqlMapConfig.xml

<?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>
    <!--配置环境-->
    <environments default="mysql">
        <!--配置mysql的环境-->
        <environment id="mysql">
            <!--配置事务-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;characterEncoding=utf-8&amp;useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <!--配置映射文件的位置-->
    <mappers>
        <mapper resource="com/uek/dao/IUserDao.xml"></mapper>
    </mappers>
</configuration>

dao层接口

public interface IUserDao {

    //查询所有用户
    List<User> findAll();

    //根据id查询用户信息
    User findById(Integer userId);

    //根据名称模糊查询用户信息
    List<User>findByName(String username);

    //根据QueryVo中的条件查询用户
    List<User> findUserByVo(QueryVo Vo);

    //根据传入的条件进行查询
    List<User>findByContition(User user);

    //根据queryvo中提供的id集合，查询用户信息
    List<User> findUserInIds(QueryVo vo);
}

实体类

public class User implements Serializable {

    private Integer id;
    private String username;
    private String address;
    private String sex;
    private Date birthday;

    public Integer getId() {
        return id;
    }

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

    public String getUsername(String mybatis_saveuser) {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

public class QueryVo {

    private User user;

    private List<Integer> ids;

    public User getUser() {
        return user;
    }

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

    public List<Integer> getIds() {
        return ids;
    }

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

接口配置 IUserDao.xml

注意：在resource目录下新建包时一级一级的建立
必须和dao层的接口的包名一致。

<?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.uek.dao.IUserDao">

    <!--抽取重复的sql语句-->
    <sql id="defaultUser">
        select * from user
    </sql>

    <!--查询所有方法-->
    <select id="findAll" resultType="com.uek.domian.User">
        <!--select * from user-->
        <include refid="defaultUser"></include>
    </select>

    <!--根据id查询用户信息-->
    <select id="findById" parameterType="int" resultType="com.uek.domian.User">
        select * from user where id = #{uid}
    </select>

    <!--根据名称模糊查询-->
    <select id="findByName" parameterType="string" resultType="com.uek.domian.User">
        select * from user where username like #{name}
        <!--select * from user where username like '%${value}%'   了解-->
    </select>

    <!--根据QueryVo的条件查询用户   OGNL表达式-->
    <select id="findUserByVo" parameterType="com.uek.domian.QueryVo" resultType="com.uek.domian.User">
        select * from user where username like #{user.username}
    </select>

    <!--根据传入的条件就行查询-->
    <!--<select id="findByContition" resultType="com.uek.domian.User">
        select * from user where 1=1
        <if test="username != null">
            and username = #{username}
        </if>
        <if test="sex != null">
            and sex = #{sex}
        </if>
    </select>-->

    <select id="findByContition" resultType="com.uek.domian.User">
        select * from user
        <where>
            <if test="username != null">
                and username = #{username}
            </if>
            <if test="sex != null">
                and sex = #{sex}
            </if>
        </where>
    </select>


    <!--根据queryvo中的id集合实现查询用户列表-->
    <select id="findUserInIds"  resultType="com.uek.domian.User">
        select * from user
        <where>
            <if test="ids != null and ids.size()>0">
                <foreach collection="ids" open="and id in (" close=")" item="id" separator=",">
                    #{id}
                </foreach>
            </if>
        </where>
    </select>
</mapper>

测试类

public class MyBatisTest {

    private InputStream in;
    private SqlSession sqlSession;
    private IUserDao userDao;

    @Before   
    public void init() throws Exception {
        //1.读取配置文件，生成字节输入流
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.获取SqlSession对象
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        //3.获取SqlSession对象
        sqlSession = factory.openSession();
        //4.获取dao的代理对象
        userDao = sqlSession.getMapper(IUserDao.class);
    }


    @After 
    public void destroy() throws Exception {
        //提交事务
        sqlSession.commit();

        //6.释放资源
        sqlSession.close();
        in.close();
    }

    //测试：查询所有
    @Test
    public void testFindAll() throws Exception {
        //执行查询所有方法
        List<User>users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
        }
    }

    //测试：查询一个操作
    @Test
    public void testSelectOne(){
        //执行查询一个方法
        User byId = userDao.findById(8);
        System.out.println(byId);
    }

    //测试:模糊查询操作
    @Test
    public void testFindByName(){
        List<User>users = userDao.findByName("%王%");
        for (User user : users) {
            System.out.println(user);
        }
    }

    //测试:使用QueryVo作为查询条件
    @Test
    public void testQueryVo(){
        QueryVo vo = new QueryVo();
        User user = new User();
        user.setUsername("%王%");
        vo.setUser(user);
        List<User>users = userDao.findUserByVo(vo);
        for (User u : users) {
            System.out.println(u);
        }
    }

    //根据条件进行查询
    @Test
    public void testByContition(){
        User u = new User();
        u.setUsername("老王");
        u.setSex("女");
        List<User> users = userDao.findByContition(u);
        for (User user : users) {
            System.out.println(user);
        }
    }

    //测试：foreach标签的使用
    @Test
    public void testForeach(){
        QueryVo vo = new QueryVo();
        List<Integer> list = new ArrayList<Integer>();
        list.add(1);
        list.add(2);
        list.add(3);
        list.add(4);
        list.add(5);
        vo.setIds(list);

        List<User> users = userDao.findUserInIds(vo);
        for (User user : users) {
            System.out.println(user);
        }
    }
}