动态SQL语句是动态的拼接Mybatis中SQL语句的情况,可以动态的在Mybatis中使用SQL
if语句的xml文件:
<select id="getEmpByCondition" resultType="Emp">
select * from t_emp where 1 = 1
<if test="empName != null and empName != ''">
emp_name = #{empName}
if>
<if test="sex != null and sex != ''">
and sex = #{sex}
if>
<if test="age != null and age != ''">
and age = #{age}
if>
<if test="email != null and email != ''">
and email = #{email}
if>
select>
传入对象来进行调用:
@Test
public void test() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
List<Emp> empList = mapper.getEmpByCondition(new Emp(null, "", 23, "男", "[email protected]", null));
System.out.println(empList);
}
where标签中的and会被自动去掉,并且若没有合适的内容,则不会添加where关键字
注意:where标签只能去掉条件前的and、五福去掉条件后的and
<select id="getEmpByCondition" resultType="Emp">
select * from t_emp
<where>
<if test="empName != null and empName != ''">
emp_name = #{empName}
if>
<if test="sex != null and sex != ''">
and sex = #{sex}
if>
<if test="age != null and age != ''">
and age = #{age}
if>
<if test="email != null and email != ''">
and email = #{email}
if>
where>
select>
trim标签会在其内容中没有合适的内容时不添加其内容,若trim标签内有内容时,则会添加这个内容
<select id="getEmpByCondition" resultType="Emp">
select * from t_emp
<trim prefix="where" suffixOverrides="and|or">
<if test="empName != null and empName != ''">
emp_name = #{empName} and
if>
<if test="sex != null and sex != ''">
sex = #{sex} or
if>
<if test="age != null and age != ''">
age = #{age} and
if>
<if test="email != null and email != ''">
email = #{email}
if>
trim>
select>
choose是when和otherwise的父标签,when和otherwise要写在choose中,相当于编程语言中的if…else…if…else…
<select id="getEmpByChoose" resultType="Emp">
select * from t_emp
<where>
<choose>
<when test="empName != null and empName != ''">
emp_name = #{empName}
when>
<when test="sex != null and sex != ''">
sex = #{sex}
when>
<otherwise>
did = 1
otherwise>
choose>
where>
select>
注意这里when至少有一个、otherwise至多有一个,也可以没有
mapper接口:
/**
* 通过数组实现批量删除(形参传入数组)
*/
int deleteMoreByArray(@Param("eids") Integer[] eids);
xml:
<delete id="deleteMoreByArray">
DELETE from t_emp where eid in
<foreach collection="eids" item="eid" separator="," open="(" close=")">
#{eid}
foreach>
delete>
xml的第二种写法:
<delete id="deleteMoreByArray">
delete from t_emp where
<foreach collection="eids" item="eid" separator="or">
eid = #{eid}
foreach>
delete>
建立接口:
/**
* 通过list实现批量添加
*/
int insertMoreByList(@Param("emps") List<Emp> list);
建立xml:
<insert id="insertMoreByList">
insert into t_emp values
<foreach collection="emps" item="emp" separator=",">
(null, #{emp.empName}, #{emp.age}, #{emp.sex}, #{emp.email}, null)
foreach>
insert>
sql标签用来将常用的一些字段记录,下次在有这些字段出现时可以简易的替换这些字段:
使用include标签来引用定义的sql片段
<sql id="empColumn">eid, emp_name, age, sex, emailsql>
<select id="getEmpByConditionOne" resultType="Emp">
select <include refid="empColumn">include> from t_emp
select>