1.if
注意要做不等于空字符串校验。
<!-- 传递pojo综合查询用户信息 --> <select id="findUserList" parameterType="user" resultType="user"> select * from user where 1=1 <if test="id!=null and id!=''"> and id=#{id} </if> <if test="username!=null and username!=''"> and username like '%${username}%' </if> </select>2.where
上边的sql也可以改为:
<select id="findUserList" parameterType="user" resultType="user"> select * from user <where> <if test="id!=null and id!=''"> and id=#{id} </if> <if test="username!=null and username!=''"> and username like '%${username}%' </if> </where> </select>
<where />可以自动处理第一个and。
3.foreach
向sql传递数组或List,mybatis使用foreach解析,如下:
3.1 通过pojo传递list
传入多个id查询用户信息,用下边两个sql实现:
SELECT * FROM USERS WHERE username LIKE '%张%' AND (id=10 OR id =89 OR id=16)
SELECT * FROM USERS WHERE username LIKE '%张%' id IN (10,89,16)
在pojo中定义list属性ids存储多个用户id,并添加getter/setter方法
mapper.xml
<if test="ids!=null and ids.size>0"> <foreach collection="ids" open=" and id in(" close=")" item="id" separator="," > #{id} </foreach> </if>
测试代码:
List<Integer> ids = new ArrayList<Integer>(); ids.add(1);//查询id为1的用户 ids.add(10); //查询id为10的用户 queryVo.setIds(ids); List<User> list = userMapper.findUserList(queryVo);
3.2 传递单个List
传递List类型在编写mapper.xml没有区别,唯一不同的是只有一个List参数时它的参数名为list。
Mapper.xml
<select id="selectUserByList" parameterType="java.util.List" resultType="user"> select * from user <where> <!-- 传递List,List中是pojo --> <if test="list!=null"> <foreach collection="list" item="item" open="and id in("separator=","close=")"> #{item.id} </foreach> </if> </where> </select>
Mapper接口
public List<User> selectUserByList(List userlist) throws Exception;
测试:
Public void testselectUserByList()throws Exception{ //获取session SqlSession session = sqlSessionFactory.openSession(); //获限mapper接口实例 UserMapper userMapper = session.getMapper(UserMapper.class); //构造查询条件List List<User> userlist = new ArrayList<User>(); User user = new User(); user.setId(1); userlist.add(user); user = new User(); user.setId(2); userlist.add(user); //传递userlist列表查询用户列表 List<User>list = userMapper.selectUserByList(userlist); //关闭session session.close(); }
3.3 传递单个数组,数组中是pojo
Mapper.xml
<!-- 传递数组综合查询用户信息 --> <select id="selectUserByArray" parameterType="Object[]" resultType="user"> select * from user <where> <!-- 传递数组 --> <if test="array!=null"> <foreach collection="array" index="index" item="item" open="and id in("separator=","close=")"> #{item.id} </foreach> </if> </where> </select>
sql只接收一个数组参数,这时sql解析参数的名称mybatis固定为array,如果数组是通过一个pojo传递到sql则参数的名称为pojo中的属性名。
index:为数组的下标。
item:为数组每个元素的名称,名称随意定义
open:循环开始
close:循环结束
separator :中间分隔输出Mapper接口:
public List<User> selectUserByArray(Object[] userlist) throws Exception;
测试:
Public void testselectUserByArray()throws Exception{ //获取session SqlSession session = sqlSessionFactory.openSession(); //获限mapper接口实例 UserMapper userMapper = session.getMapper(UserMapper.class); //构造查询条件List Object[] userlist = new Object[2]; User user = new User(); user.setId(1); userlist[0]=user; user = new User(); user.setId(2); userlist[1]=user; //传递user对象查询用户列表 List<User>list = userMapper.selectUserByArray(userlist); //关闭session session.close(); }3.4 传递单个数组(数组中是字符串类型)
Mapper.xml
<!-- 传递数组综合查询用户信息 --> <select id="selectUserByArray" parameterType="Object[]" resultType="user"> select * from user <where> <!-- 传递数组 --> <if test="array!=null"> <foreach collection="array"index="index"item="item"open="and id in("separator=","close=")"> #{item} </foreach> </if> </where> </select>
如果数组中是简单类型则写为#{item},不用再通过ognl获取对象属性值了。
Mapper接口:
public List<User> selectUserByArray(Object[] userlist) throws Exception;
测试:
Public void testselectUserByArray()throws Exception{ //获取session SqlSession session = sqlSessionFactory.openSession(); //获限mapper接口实例 UserMapper userMapper = session.getMapper(UserMapper.class); //构造查询条件List Object[] userlist = new Object[2]; userlist[0]=”1”; userlist[1]=”2”; //传递user对象查询用户列表 List<User>list = userMapper.selectUserByArray(userlist); //关闭session session.close(); }
4.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,如下:
<!-- 传递pojo综合查询用户信息 --> <select id="findUserList" parameterType="user" resultType="user"> select * from user <where> <if test="id!=null and id!=''"> and id=#{id} </if> <if test="username!=null and username!=''"> and username like '%${username}%' </if> </where> </select>
将where条件抽取出来:
<sql id="query_user_where"> <if test="id!=null and id!=''"> and id=#{id} </if> <if test="username!=null and username!=''"> and username like '%${username}%' </if> </sql>使用include引用:
<select id="findUserList" parameterType="user" resultType="user"> select * from user <where> <include refid="query_user_where"/> </where> </select>
注意:如果引用其它mapper.xml的sql片段,则在引用时需要加上namespace,如下:
<includerefid="namespace.sql片段”/>
5.关于 关联查询,其实和单表差不多,只是pojo里面要加入查询到的所有信息;
6.延迟加载--------待续