4、动态sql
4、动态sql
4.1 动态sql-简介&环境搭建
- 动态SQL是MyBatis强大特性之一。极大的简化我们拼装SQL的操作。
- 动态SQL元素和使用 JSTL 或其他类似基于 XML 的文本处理器相似。
- MyBatis采用功能强大的基于 OGNL 的表达式来简化操作。
- if
- choose (when, otherwise)
- trim (where, set)
- foreach
4.2 动态sql-if-判断&OGNL
DynamicSQLMapper.java
public interface DynamicSQLMapper {
//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);
}
DynamicSQLMapper.xml
<mapper namespace="club.coderhome.c04.dynamicsql.DynamicSQLMapper">
<select id="getEmpsByConditionIf" resultType="club.coderhome.c01.helloworld.bean.Employee">
select * from employee where
<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>
<if test="gender==0 or gender==1">
and gender=#{gender}
if>
select>
mapper>
DynamicSQLMapperTest.java
public class DynamicSQLMapperTest {
@Test
public void testGetEmpsByConditionIf() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
Employee employee = new Employee(1, "jallen", null, null);
System.out.println(dsm.getEmpsByConditionIf(employee));
session.commit();
} finally {
session.close();
}
}
}
OGNL
OGNL官方文档
OGNL（ Object Graph Navigation Language ）对象图导航语言， 这是一种强大的表达式语言，通过它可以非常方便的来操作对象属性。 类似于我们的EL， SpEL等。
- 访问对象属性： person.name
- 调用方法： person.getName()
- 调用静态属性/方法： @java.lang.Math@PI、@java.util.UUID@randomUUID()
- 调用构造方法： new club.coderhome.Person(‘admin’).name
- 运算符： +, -*, /, %
- 逻辑运算符： in, not in, >, >=, <, <=, ==, !=
注意： xml中特殊符号如”,>,<等这些都需要使用转义字符
访问集合伪属性：
| 类型 | 伪属性 | 伪属性对应的 Java 方法 |
|---|---|---|
| List、 Set、 Map | size、 isEmpty | List/Set/Map.size(),List/Set/Map.isEmpty() |
| List、 Set | iterator | List.iterator()、 Set.iterator() |
| Map | keys、 values | Map.keySet()、 Map.values() |
| Iterator | next、 hasNext | Iterator.next()、 Iterator.hasNext() |
4.3 动态sql-where-查询条件
查询的时候如果某些条件没带可能sql拼装会有问题
- 给where后面加上1=1，以后的条件都and xxx。
- 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，但最后一个多出来的and或者or则不会去掉）。
DynamicSQLMapper.xml
<mapper namespace="club.coderhome.c04.dynamicsql.DynamicSQLMapper">
<select id="getEmpsByConditionIfWithWhere" resultType="club.coderhome.c01.helloworld.bean.Employee">
select * from employee
<where>
<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>
<if test="gender==0 or gender==1">
and gender=#{gender}
if>
where>
select>
select>
DynamicSQLMapper.java
public interface DynamicSQLMapper {
public List<Employee> getEmpsByConditionIfWithWhere(Employee employee);
DynamicSQLMapperTest.java
public class DynamicSQLMapperTest {
@Test
public void testGetEmpsByConditionIfWithWhere() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
Employee employee = new Employee(null, "jallen", null, null);
System.out.println(dsm.getEmpsByConditionIfWithWhere(employee));
session.commit();
} finally {
session.close();
}
}
...
4.4 动态sql-trim-自定义字符串截取
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
DynamicSQLMapper.java
public interface DynamicSQLMapper {
public List<Employee> getEmpsByConditionTrim(Employee employee);
...
DynamicSQLMapper.xml
<mapper namespace="club.coderhome.c04.dynamicsql.DynamicSQLMapper">
<select id="getEmpsByConditionTrim" resultType="club.coderhome.c01.helloworld.bean.Employee">
select * from employee
<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>
<if test="gender==0 or gender==1">
gender=#{gender}
if>
trim>
select>
...
DynamicSQLMapperTest.java
public class DynamicSQLMapperTest {
@Test
public void testGetEmpsByConditionTrim() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
Employee employee = new Employee(1, "jallen", null, null);
System.out.println(dsm.getEmpsByConditionTrim(employee));
session.commit();
} finally {
session.close();
}
}
...
4.5 动态sql-choose-分支选择
DynamicSQLMapper.java
public interface DynamicSQLMapper {
public List<Employee> getEmpsByConditionChoose(Employee employee);
...
DynamicSQLMapper.xml
<mapper namespace="club.coderhome.c04.dynamicsql.DynamicSQLMapper">
<select id="getEmpsByConditionChoose" resultType="club.coderhome.c01.helloworld.bean.Employee">
select * from employee
<where>
<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>
DynamicSQLMapperTest.java
public class DynamicSQLMapperTest {
@Test
public void testGetEmpsByConditionChoose() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
Employee employee = new Employee(1, "jallen", null, null);
System.out.println(dsm.getEmpsByConditionChoose(employee));
session.commit();
} finally {
session.close();
}
}
4.6 动态sql-set-与if结合的动态更新
DynamicSQLMapper.java
public interface DynamicSQLMapper {
public void updateEmp(Employee employee);
DynamicSQLMapper.xml
<mapper namespace="club.coderhome.c04.dynamicsql.DynamicSQLMapper">
<update id="updateEmp">
update 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}
update>
DynamicSQLMapperTest.java
public class DynamicSQLMapperTest {
@Test
public void testUpdateEmp() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
Employee employee = new Employee(1, "jallen2", null, null);
dsm.updateEmp(employee);
session.commit();
} finally {
session.close();
}
}
4.7 动态sql-foreach-遍历集合
- 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
DynamicSQLMapper.java
public interface DynamicSQLMapper {
public List<Employee> getEmpsByConditionForeach(@Param("ids")List<Integer> ids);
DynamicSQLMapper.xml
<mapper namespace="club.coderhome.c04.dynamicsql.DynamicSQLMapper">
<!--public List<Employee> getEmpsByConditionForeach(List<Integer> ids); -->
<select id="getEmpsByConditionForeach" resultType="club.coderhome.c01.helloworld.bean.Employee">
select * from employee
<foreach collection="ids" item="item_id" separator=","
open="where id in(" close=")">
#{item_id}
</foreach>
</select>
DynamicSQLMapperTest.java
public class DynamicSQLMapperTest {
@Test
public void testGetEmpsByConditionForeach() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
System.out.println(dsm.getEmpsByConditionForeach(Arrays.asList(1,2,3)));
session.commit();
} finally {
session.close();
}
}
4.8 动态sql-foreach-mysql下foreach批量插入的两种方式
DynamicSQLMapper.java
public interface DynamicSQLMapper {
public void addEmps(@Param("emps")List<Employee> emps);
public void addEmps2(@Param("emps")List<Employee> emps);
DynamicSQLMapper.xml
<mapper namespace="club.coderhome.c04.dynamicsql.DynamicSQLMapper">
<insert id="addEmps">
insert into employee(last_name,email,gender,department_id)
values
<foreach collection="emps" item="emp" separator=",">
(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.department.id})
foreach>
insert>
<insert id="addEmps2">
<foreach collection="emps" item="emp" separator=";">
insert into employee(last_name,email,gender,department_id)
values(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.department.id})
foreach>
insert>
注意，MySQL数据库连接属性allowMultiQueries=true，才能批量删除，修改数据。（在连接MySQL的URL后添加参数）。
DynamicSQLMapperTest.java
public class DynamicSQLMapperTest {
@Test
public void testAddEmps2() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
dsm.addEmps2(Arrays.asList(new Employee(null, "abc", null, null),
new Employee(null, "cba",null, null)));
session.commit();
} finally {
session.close();
}
}
@Test
public void testAddEmps() throws IOException {
SqlSessionFactory ssf = Tools.getSqlSessionFactory("c04/mybatis-config.xml");
SqlSession session = ssf.openSession();
try {
DynamicSQLMapper dsm = session.getMapper(DynamicSQLMapper.class);
dsm.addEmps(Arrays.asList(new Employee(null, "abc", null, null),
new Employee(null, "cba",null, null)));
session.commit();
} finally {
session.close();
}
}
4.9 动态sql-foreach-oracle下批量插入的两种方式
Oracle数据库批量保存：
- Oracle不支持values(),(),()
Oracle支持的批量方式:
- 多个insert放在begin - end里面
- 利用中间表
# 多个insert放在begin - end里面
begin
insert into employees(employee_id,last_name,email)
values(employees_seq.nextval,'test_001','[email protected]');
insert into employees(employee_id,last_name,email)
values(employees_seq.nextval,'test_002','[email protected]');
end;
# 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
);
4.10 动态sql-foreach-oracle下foreach批量保存两种方式
<insert id="addEmps" databaseId="oracle">
insert into employees(employee_id,last_name,email)
<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>
4.11 动态sql-内置参数 _parameter & _databaseId
不只是方法传递过来的参数可以被用来判断，
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
<select id="getEmpsTestInnerParameter" resultType="club.coderhome.c01.helloworld.bean.Employee">
<if test="_databaseId=='mysql'">
select * from tbl_employee
<if test="_parameter!=null">
where last_name like #{_parameter.lastName}
if>
if>
<if test="_databaseId=='oracle'">
select * from employees
<if test="_parameter!=null">
where last_name like #{_parameter.lastName}
if>
if>
select>
4.12 动态sql-bind-绑定
<select id="getEmpsTestInnerParameter" resultType="com.atguigu.mybatis.bean.Employee">
<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>
4.13 动态sql-sql-抽取可重用的sql片段
抽取可重用的sql片段。方便后面引用：
- 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
- include来引用已经抽取的sql：
- 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${prop},
- 不能使用
#{}，而使用${}
<sql id="userColumns"> ${alias}.id,${alias}.username,${alias}.password </sql>
<select id="selectUsers" resultType="map">
select
<include refid="userColumns"><property name="alias" value="t1"/></include>,
<include refid="userColumns"><property name="alias" value="t2"/></include>
from some_table t1
cross join some_table t2
</select>
<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 id="addEmps">
insert into tbl_employee(
<include refid="insertColumn"></include><!-- 使用地方 -->
)
values
<foreach collection="emps" item="emp" separator=",">
(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
</foreach>
</insert>