if和where
//携带了哪个字段查询条件就带上这个字段的值
public List<Employee> getEmpsByConditionIf(Employee employee);
<!-- 查询员工，要求，携带了哪个字段查询条件就带上这个字段的值 -->
<!-- public List<Employee> getEmpsByConditionIf(Employee employee); -->
<select id="getEmpsByConditionIf" resultType="com.atguigu.mybatis.bean.Employee">
select * from tbl_employee
<!-- where -->
<where>
<!-- test：判断表达式（OGNL）
OGNL参照PPT或者官方文档。
c:if test
从参数中取值进行判断
遇见特殊符号应该去写转义字符：
&&：&&
-->
<if test="id!=null">
id=#{id}
</if>
<if test="lastName!=null && lastName!=""">
and last_name like #{lastName}
</if>
<if test="email!=null and email.trim()!=""">
and email=#{email}
</if>
<!-- ognl会进行字符串与数字的转换判断 "0"==0 -->
<if test="gender==0 or gender==1">
and gender=#{gender}
</if>
</where>
</select>
@Test
public void testDynamicSql() throws IOException{
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try{
EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
//select * from tbl_employee where id=? and last_name like ?
//测试if\where
Employee employee = new Employee(1, "Admin", null, null);
/* List<Employee> emps = mapper.getEmpsByConditionIf(employee );
for (Employee emp : emps) {
System.out.println(emp);
}*/
//查询的时候如果某些条件没带可能sql拼装会有问题
//1、给where后面加上1=1，以后的条件都and xxx.
//2、mybatis使用where标签来将所有的查询条件包括在内。mybatis就会将where标签中拼装的sql，多出来的and或者or去掉
//where只会去掉第一个多出来的and或者or。
trim字符串截取
- 字符串截取(where(封装查询条件), set(封装修改条件))
选择性查询
public List<Employee> getEmpsByConditionTrim(Employee employee);
<!--public List<Employee> getEmpsByConditionTrim(Employee employee); -->
<select id="getEmpsByConditionTrim" resultType="com.atguigu.mybatis.bean.Employee">
select * from tbl_employee
<!-- 后面多出的and或者or where标签不能解决
prefix="":前缀：trim标签体中是整个字符串拼串 后的结果。
prefix给拼串后的整个字符串加一个前缀
prefixOverrides="":
前缀覆盖： 去掉整个字符串前面多余的字符
suffix="":后缀
suffix给拼串后的整个字符串加一个后缀
suffixOverrides=""
后缀覆盖：去掉整个字符串后面多余的字符
-->
<!-- 自定义字符串的截取规则 -->
<trim prefix="where" suffixOverrides="and">
<if test="id!=null">
id=#{id} and
</if>
<if test="lastName!=null && lastName!=""">
last_name like #{lastName} and
</if>
<if test="email!=null and email.trim()!=""">
email=#{email} and
</if>
<!-- ognl会进行字符串与数字的转换判断 "0"==0 -->
<if test="gender==0 or gender==1">
gender=#{gender}
</if>
</trim>
</select>
//测试Trim
Employee employee = new Employee(1, "Admin", null, null);
List<Employee> emps2 = mapper.getEmpsByConditionTrim(employee);
for (Employee emp : emps2) {
System.out.println(emp);
}
选择性插入
<insert id="insertSelective" parameterType="com.zjl.domain">
insert into table_name
<trim prefix="(" suffix=")" suffixOverrides=",">
<if test="id != null">
id,
</if>
<if test="createDate != null">
create_date,
</if>
<if test="modifiedDate != null">
modified_date,
</if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides=",">
<if test="id != null">
#{id,jdbcType=BIGINT},
</if>
<if test="createDate != null">
#{createDate,jdbcType=TIMESTAMP},
</if>
<if test="modifiedDate != null">
#{modifiedDate,jdbcType=TIMESTAMP},
</if>
</trim>
</insert>
插入包含子查询
- 添加数据时默认添加排列顺序：查询表中数据的最大排序号+1
<insert id="insertArsDept" parameterType="ArsDept" useGeneratedKeys="true" keyProperty="deptId">
insert into ars_dept
<trim prefix="(" suffix=")" suffixOverrides=",">
<if test="parentId != null ">parent_id,</if>
<if test="deptName != null and deptName != ''">dept_name,</if>
<if test="deptAlias != null and deptAlias != ''">dept_alias,</if>
<if test="inputCode != null and inputCode != ''">input_code,</if>
<if test="fullCode != null and fullCode != ''">full_code,</if>
order_num,
<!-- <if test="orderNum != null ">order_num,</if> -->
<if test="deptDescription != null and deptDescription != ''">dept_description,</if>
<if test="status != null and status != ''">status,</if>
<if test="delFlag != null and delFlag != ''">del_flag,</if>
<if test="createBy != null and createBy != ''">create_by,</if>
<if test="createTime != null ">create_time,</if>
<if test="updateBy != null and updateBy != ''">update_by,</if>
<if test="updateTime != null ">update_time,</if>
<if test="deptClassId != null ">dept_class_id,</if>
</trim>
<trim prefix="select " suffixOverrides=",">
<if test="parentId != null ">#{parentId},</if>
<if test="deptName != null and deptName != ''">#{deptName},</if>
<if test="deptAlias != null and deptAlias != ''">#{deptAlias},</if>
<if test="inputCode != null and inputCode != ''">#{inputCode},</if>
<if test="fullCode != null and fullCode != ''">#{fullCode},</if>
IFNULL((select MAX(order_num)+1 from ars_dept),0),
<!-- <if test="orderNum != null ">#{orderNum},</if> -->
<if test="deptDescription != null and deptDescription != ''">#{deptDescription},</if>
<if test="status != null and status != ''">#{status},</if>
<if test="delFlag != null and delFlag != ''">#{delFlag},</if>
<if test="createBy != null and createBy != ''">#{createBy},</if>
<if test="createTime != null ">#{createTime},</if>
<if test="updateBy != null and updateBy != ''">#{updateBy},</if>
<if test="updateTime != null ">#{updateTime},</if>
<if test="deptClassId != null ">#{deptClassId},</if>
</trim>
</insert>
choose多分支
public List<Employee> getEmpsByConditionChoose(Employee employee);
<!-- public List<Employee> getEmpsByConditionChoose(Employee employee); -->
<select id="getEmpsByConditionChoose" resultType="com.atguigu.mybatis.bean.Employee">
select * from tbl_employee
<where>
<!-- 如果带了id就用id查，如果带了lastName就用lastName查;只会进入其中一个相当于switch -->
<choose>
<when test="id!=null">
id=#{id}
</when>
<when test="lastName!=null">
last_name like #{lastName}
</when>
<when test="email!=null">
email = #{email}
</when>
<otherwise>
gender = 0
</otherwise>
</choose>
</where>
</select>
//测试choose
Employee employee = new Employee(1, "Admin", null, null);
List<Employee> list = mapper.getEmpsByConditionChoose(employee);
for (Employee emp : list) {
System.out.println(emp);
}
//select * from tbl_employee where id=1
set选择性更新
- 主要用于选择性更新，对象中哪几个字段不为空就更新哪几个字段
public void updateEmp(Employee employee);
<!--public void updateEmp(Employee employee); -->
<update id="updateEmp">
<!-- Set标签的使用 -->
update tbl_employee
<set>
<if test="lastName!=null">
last_name=#{lastName},
</if>
<if test="email!=null">
email=#{email},
</if>
<if test="gender!=null">
gender=#{gender}
</if>
</set>
where id=#{id}
<!--
Trim：更新拼串
update tbl_employee
<trim prefix="set" suffixOverrides=",">
<if test="lastName!=null">
last_name=#{lastName},
</if>
<if test="email!=null">
email=#{email},
</if>
<if test="gender!=null">
gender=#{gender}
</if>
</trim>
where id=#{id}
-->
</update>
//测试set标签
Employee employee = new Employee(1, "Admin", null, null);
mapper.updateEmp(employee);
openSession.commit();
foreach遍历集合
//查询员工id在给定集合中的
public List<Employee> getEmpsByConditionForeach(@Param("ids")List<Integer> ids);
<!--public List<Employee> getEmpsByConditionForeach(List<Integer> ids); -->
<select id="getEmpsByConditionForeach" resultType="com.atguigu.mybatis.bean.Employee">
select * from tbl_employee
<!--
collection：指定要遍历的集合：
list类型的参数会特殊处理封装在map中，map的key就叫list
item：将当前遍历出的元素赋值给指定的变量
separator:每个元素之间的分隔符
open：遍历出所有结果拼接一个开始的字符
close:遍历出所有结果拼接一个结束的字符
index:索引。遍历list的时候是index就是索引，item就是当前值
遍历map的时候index表示的就是map的key，item就是map的值
#{变量名}就能取出变量的值也就是当前遍历出的元素
-->
<foreach collection="ids" item="item_id" separator=","
open="where id in(" close=")">
#{item_id}
</foreach>
</select>
//测试foreach
List<Employee> list = mapper.getEmpsByConditionForeach(Arrays.asList(1,2));
for (Employee emp : list) {
System.out.println(emp);
}
//select * from tbl_employee where id in(1,2)
批量保存
public void addEmps(@Param("emps")List<Employee> emps);
<!-- 批量保存 -->
<!--public void addEmps(@Param("emps")List<Employee> emps); -->
<!--MySQL下批量保存：可以foreach遍历 mysql支持values(),(),()语法-->
<insert id="addEmps">
insert into tbl_employee(
last_name,email,gender,d_id
)
values
<foreach collection="emps" item="emp" separator=",">
(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
</foreach>
</insert>
<!-- 这种方式需要数据库连接属性allowMultiQueries=true；
jdbc.url=jdbc:mysql://localhost:3306/mybatis?allowMultiQueries=true
这种分号分隔多个sql可以用于其他的批量操作（删除，修改） -->
<insert id="addEmps">
<foreach collection="emps" item="emp" separator=";">
insert into tbl_employee(last_name,email,gender,d_id)
values(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
</foreach>
</insert>
@Test
public void testBatchSave() throws IOException{
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try{
EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
List<Employee> emps = new ArrayList<>();
emps.add(new Employee(null, "smith0x1", "smith0x1@atguigu.com", "1",new Department(1)));
emps.add(new Employee(null, "allen0x1", "allen0x1@atguigu.com", "0",new Department(1)));
mapper.addEmps(emps);
openSession.commit();
}finally{
openSession.close();
}
}
oracle
public void addEmps(@Param("emps")List<Employee> emps);
Oracle数据库批量保存：
Oracle不支持values(),(),()
Oracle支持的批量方式
1、多个insert放在begin - end里面
begin
insert into employees(employee_id,last_name,email)
values(employees_seq.nextval,'test_001','test_001@atguigu.com');
insert into employees(employee_id,last_name,email)
values(employees_seq.nextval,'test_002','test_002@atguigu.com');
end;
2、利用中间表：
insert into employees(employee_id,last_name,email)
select employees_seq.nextval,lastName,email from(
select 'test_a_01' lastName,'test_a_e01' email from dual
union
select 'test_a_02' lastName,'test_a_e02' email from dual
union
select 'test_a_03' lastName,'test_a_e03' email from dual
)
<insert id="addEmps" databaseId="oracle">
<!-- oracle第一种批量方式 -->
<foreach collection="emps" item="emp" open="begin" close="end;">
insert into employees(employee_id,last_name,email)
values(employees_seq.nextval,#{emp.lastName},#{emp.email});
</foreach>
</insert>
<insert id="addEmps" databaseId="oracle">
<!-- oracle第二种批量方式 -->
insert into employees(
<!-- 引用外部定义的sql -->
<include refid="insertColumn">
<property name="testColomn" value="abc"/>
</include>
)
<foreach collection="emps" item="emp" separator="union"
open="select employees_seq.nextval,lastName,email from("
close=")">
select #{emp.lastName} lastName,#{emp.email} email from dual
</foreach>
</insert>
内置参数
两个内置参数：
不只是方法传递过来的参数可以被用来判断，取值。。。
mybatis默认还有两个内置参数：
_parameter:代表整个参数
单个参数：_parameter就是这个参数
多个参数：参数会被封装为一个map；_parameter就是代表这个map
_databaseId:如果配置了databaseIdProvider标签。
_databaseId就是代表当前数据库的别名oracle
public List<Employee> getEmpsTestInnerParameter(Employee employee);
<!--public List<Employee> getEmpsTestInnerParameter(Employee employee); -->
<select id="getEmpsTestInnerParameter" resultType="com.atguigu.mybatis.bean.Employee">
<!-- bind：可以将OGNL表达式的值绑定到一个变量中，方便后来引用这个变量的值 -->
<bind name="_lastName" value="'%'+lastName+'%'"/>
<if test="_databaseId=='mysql'">
select * from tbl_employee
<if test="_parameter!=null">
where last_name like #{lastName}
</if>
</if>
<if test="_databaseId=='oracle'">
select * from employees
<if test="_parameter!=null">
where last_name like #{_parameter.lastName}
</if>
</if>
</select>
@Test
public void testInnerParam() throws IOException{
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession openSession = sqlSessionFactory.openSession();
try{
EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
Employee employee2 = new Employee();
employee2.setLastName("e");
List<Employee> list = mapper.getEmpsTestInnerParameter(employee2);
for (Employee employee : list) {
System.out.println(employee);
}
}finally{
openSession.close();
}
}
重用sql
抽取可重用的sql片段。方便后面引用
1、sql抽取：经常将要查询的列名，或者插入用的列名抽取出来方便引用
2、include来引用已经抽取的sql：
3、include还可以自定义一些property，sql标签内部就能使用自定义的属性
include-property：取值的正确方式${prop},
#{不能使用这种方式}
<sql id="insertColumn">
<if test="_databaseId=='oracle'">
employee_id,last_name,email
</if>
<if test="_databaseId=='mysql'">
last_name,email,gender,d_id
</if>
</sql>
insert into employees(
<!-- 引用外部定义的sql -->
<include refid="insertColumn">
<!--<property name="testColomn" value="abc"/>-->
</include>
)
insert into tbl_employee(
<include refid="insertColumn"></include>
)
转义字符
在Mybatis编写特殊常用字符你会发现会报错,比如常用的<,>,<=,>= 等，原因是与xml文件的元素<>冲突，所以需要转义。整理转义字符如下：
| 符号 | 原始字符 | 转义字符 |
|---|---|---|
| 大于 | > | > |
| 大于等于 | >= | >= |
| 小于 | < | < |
| 小于等于 | <= | <= |
| 和 | & | & |
| 单引号 | ’ | ' |
| 双引号 | ” | " |