mybatis 动态sql

首先定义queryVo 类

package com.itheima.domain;

import java.util.List;

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;
    }
}

IUserDao定义的接口

/*
    * 根据传入参数条件查询
    * @param user 查询的条件：有可能有用户名，有可能有性别，也有可能有地址，可能啥都没有
    * */
    List<User> findUserByCondition(User user);

    /*
    * 根据queryVo中提供的id集合查询用户信息
    * */
    List<User> findUserInIds(QueryVo vo);

根据条件进行查询 IUserDao.xml

<!--根据条件查询-->
    <select id="findUserByCondition" parameterType="com.itheima.domain.User" resultMap="userMap">
        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" parameterType="com.itheima.domain.QueryVo" resultMap="userMap">
        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>

测试

@Test
    public void testFindUserByCondition(){
        User u = new User();
        u.setUsername("老王");
        List<User> users = userDao.findUserByCondition(u);
        for(User user:users)
            System.out.println(user);
    }

    @Test
    public void testFindInIds(){
        QueryVo vo = new QueryVo();
        List<Integer> list = new ArrayList<>();
        list.add(41);
        list.add(42);
        list.add(46);
        vo.setIds(list);

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