mybatis 的动态sql语句是基于OGNL表达式的。可以方便的在 sql 语句中实现某些逻辑. 总体说来mybatis 动态SQL 语句主要有以下几类:
1. if 语句 (简单的条件判断)
2. choose (when,otherwize) ,相当于java 语言中的 switch ,与 jstl 中的choose 很类似.
3. trim (对包含的内容加上 prefix,或者 suffix 等,前缀,后缀)
4. where (主要是用来简化sql语句中where条件判断的,能智能的处理 and or ,不必担心多余导致语法错误)
5. set (主要用于更新时)
6. foreach (用于mybatis语句查询)

 
1.if语句(简单的条件判断)
(1)数据库my的user表数据为:
 
 
(2)首先创建一个mybatis项目,mybatis_008

(3)建立com.zk.dao包下的IUser接口:

IUser.java

package com.zk.dao;

import org.apache.ibatis.annotations.Param;
import com.zk.pojo.User; public interface IUser {
public User findUserWithNameLike(@Param("id")int id, @Param("name")String name);
}

(4)在com.zk.pojo包下建立User实现IUser接口中的方法,并配置UserMapper.xml

User.java

package com.zk.pojo;

public class User {
private int id;
private String name;
private String level;
private String phone;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getLevel() {
return level;
}
public void setLevel(String level) {
this.level = level;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", level=" + level
+ ", phone=" + phone + "]";
}
}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zk.dao.IUser">
<select id="findUserWithNameLike" resultType="User">
SELECT * FROM user
WHERE id = #{id} <if test="name!= null">
AND name like #{name}
</if>
</select>
</mapper>

(5)配置config/configure.xml

configure.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<typeAliases>
<typeAlias alias="User" type="com.zk.pojo.User" />
</typeAliases> <environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/my"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments> <mappers>
<!-- // power by http://www.yiibai.com -->
<mapper resource="com/zk/pojo/UserMapper.xml" />
</mappers>
</configuration>

(6)实现main函数

MainApp.java

package Main;

import java.io.IOException;
import java.io.Reader; import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder; import com.zk.dao.IUser;
import com.zk.pojo.User; public class MainApp {
private static SqlSessionFactory sqlsessionfactory;
private static Reader reader; static{
try {
reader=Resources.getResourceAsReader("config/configure.xml");
sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} public SqlSessionFactory getSqlSessionFactory()
{
return sqlsessionfactory;
} public static void main(String[]args)
{
select(1,"c");
} public static void select(int id,String name){
//获取session连接
SqlSession session=sqlsessionfactory.openSession();
//获取mapper
IUser usermap=session.getMapper(IUser.class);
//selectAllUser();
User user = usermap.findUserWithNameLike(id, name);
//执行查询
System.out.println(user.toString());
session.commit();
//selectAllUser();
}
}

  Main执行结果如下:

2. where (主要是用来简化sql语句中where条件判断的,能智能的处理 and or ,不必担心多余导致语法错误)

(1) UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zk.dao.IUser">
<select id="findUserWithNameLike" resultType="User">
SELECT * FROM user
<where> <if test="id!=null">id like #{id}</if>
<if test="name!=null">AND name like #{name}</if>
</where>
</select>
</mapper>

运行结果如下:

3. choose (when,otherwize) ,相当于java 语言中的 switch ,与 jstl 中的choose 很类似.

同样原始的数据库,仅更改pojo层的UserMapper.xml,如下所示:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zk.dao.IUser">
<select id="findUserWithNameLike" resultType="User">
SELECT * FROM user where
<choose>
<when test="id!=null">
id like #{id}
</when>
<when test="name!=null">
AND name like #{name}
</when>
</choose> </select>
</mapper>

 运行后得到的结果如下图所示:

4. set (主要用于更新时)

(1)IUser.java

package com.zk.dao;

import com.zk.pojo.User;

public interface IUser {
public User updateUser(User user);
}

(2)UserMapper.xml和User.java

User.java

package com.zk.pojo;

public class User {
private int id;
private String name;
private String level;
private String phone;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getLevel() {
return level;
}
public void setLevel(String level) {
this.level = level;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", level=" + level
+ ", phone=" + phone + "]";
}
}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zk.dao.IUser">
<update id="updateUser" parameterType="User">
update user
<set>
<if test="name!=null">name=#{name},</if>
<if test="level!=null">level=#{level},</if>
<if test="phone!=null">phone=#{phone}</if>
</set>
where id=#{id}
</update>
</mapper>

(3)configure.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<typeAliases>
<typeAlias alias="User" type="com.zk.pojo.User" />
</typeAliases> <environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/my"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments> <mappers>
<mapper resource="com/zk/pojo/UserMapper.xml" />
</mappers>
</configuration>

(4)Main.java

package Main;

import java.io.IOException;
import java.io.Reader; import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder; import com.zk.dao.IUser;
import com.zk.pojo.User; public class MainApp {
private static SqlSessionFactory sqlsessionfactory;
private static Reader reader; static{
try {
reader=Resources.getResourceAsReader("config/configure.xml");
sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} public SqlSessionFactory getSqlSessionFactory()
{
return sqlsessionfactory;
} public static void main(String[]args)
{
SqlSession session=sqlsessionfactory.openSession();
User user=new User();
user.setId(1);
user.setName("a");
user.setLevel("a");
user.setPhone("137298647"); session.update("updateUser",user);
session.commit();
}
} 

运行结果如下: 

 5. trim (对包含的内容加上 prefix,或者 suffix 等,前缀,后缀)

IUser.java

package com.zk.dao;

import org.apache.ibatis.annotations.Param;
import com.zk.pojo.User; public interface IUser {
public User findUserWithNameLike(@Param("id")int id, @Param("name")String name);
}

User.java

package com.zk.pojo;

public class User {
private int id;
private String name;
private String level;
private String phone;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getLevel() {
return level;
}
public void setLevel(String level) {
this.level = level;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", level=" + level
+ ", phone=" + phone + "]";
}
}

 UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zk.dao.IUser">
<select id="findUserWithNameLike" resultType="User">
SELECT * FROM user
<trim prefix="WHERE" prefixOverrides="AND">
<if test="id!=null">
id=#{id}
</if>
<if test="name!= null">
AND name like #{name}
</if>
</trim>
</select>
</mapper>

MainApp.java

package Main;

import java.io.IOException;
import java.io.Reader; import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder; import com.zk.dao.IUser;
import com.zk.pojo.User; public class MainApp {
private static SqlSessionFactory sqlsessionfactory;
private static Reader reader; static{
try {
reader=Resources.getResourceAsReader("config/configure.xml");
sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} public SqlSessionFactory getSqlSessionFactory()
{
return sqlsessionfactory;
} public static void main(String[]args)
{
select(1,"a");
} public static void select(int id,String name){
//获取session连接
SqlSession session=sqlsessionfactory.openSession();
//获取mapper
IUser usermap=session.getMapper(IUser.class);
//selectAllUser();
User user = usermap.findUserWithNameLike(id, name);
//执行查询
System.out.println(user.toString());
session.commit();
//selectAllUser();
}
}

执行结果如下:

 6. foreach (用于mybatis语句查询)

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.zk.dao.IUser">
<select id="findUsersWithIdforeach" resultType="User">
SELECT * FROM user
<where>id in
<foreach collection="list" item="item" open="(" close=")" separator=",">
#{item}
</foreach>
</where>
</mapper>

IUser.java

package com.zk.dao;

import java.util.List;
import org.apache.ibatis.annotations.Param; import com.zk.pojo.User; public interface IUser {
public List<User> findUsersWithIdforeach(@Param("list")List<Integer> list);
}

Main.java

package Main;

import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.List; import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder; import com.zk.dao.IUser;
import com.zk.pojo.User; public class MainApp {
private static SqlSessionFactory sqlsessionfactory;
private static Reader reader; static{
try {
reader=Resources.getResourceAsReader("config/configure.xml");
sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} public SqlSessionFactory getSqlSessionFactory()
{
return sqlsessionfactory;
} public static void main(String[]args)
{
select(1,"a");
} public static void select(int id,String name){
//获取session连接
SqlSession session=sqlsessionfactory.openSession();
//获取mapper
IUser usermap=session.getMapper(IUser.class);
//selectAllUser();
List ids=new ArrayList();
ids.add(1);
ids.add(2);
ids.add(3);
ids.add(4);
//执行查询
//System.out.println(user.toString());
List<User> users=usermap.findUsersWithIdforeach(ids);
for(User u:users)
{
System.out.println(u);
}
session.commit();
//selectAllUser();
}
}

程序运行结果:

数据库中数据:

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