MyBatis 教程完全指南:从入门配置到企业级动态 SQL 实战攻略

Connection conn = DriverManager.getConnection(url,user,password);
PreparedStatement ps =
conn.prepareStatement(
    "select * from student where id=?"
);
ps.setLong(1,id);
ResultSet rs = ps.executeQuery();
while(rs.next()){
}

Student selectById(Long id);

<select id="selectById">
select *
from student
where id=#{id}
</select>

Student student =
studentMapper.selectById(1L);

Java对象
   |
   |
Mapper接口
   |
   |
MyBatis
   |
   |
SQL执行
   |
   |
ResultSet
   |
   |
Java对象

try(Connection conn = dataSource.getConnection()){
}
catch(Exception e){
}

mapper.selectList();

String sql =
"select * from student where name=?";

Mapper.java
        ↓
StudentMapper.xml

where name='Tom'

查询全部

<if test="name != null">
and name=#{name}
</if>

create_time

private Date createTime;

create_time
        ↓
createTime

Controller
    ↓
Service
    ↓
Mapper接口
    ↓
Mapper.xml
    ↓
SqlSession
    ↓
Executor
    ↓
JDBC
    ↓
Database

mybatis-demo
├── controller
├── service
├── mapper
│    └── StudentMapper.java
├── entity
│    └── Student.java
├── resources
│
├── mapper
│    └── StudentMapper.xml
└── application.yml

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>
        mybatis-spring-boot-starter
    </artifactId>
    <version>2.3.1</version>
</dependency>

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>
        mysql-connector-j
    </artifactId>
</dependency>

<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</dependency>

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/test
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver
mybatis:
  mapper-locations:
    classpath:mapper/*.xml
  type-aliases-package:
    com.demo.entity
  configuration:
    map-underscore-to-camel-case: true

resources
 └── mapper
       └── StudentMapper.xml

mapper-locations:
classpath:mapper/*.xml

classpath:/mapper/*.xml

package com.demo.entity;
public class Student{
}

type-aliases-package:
com.demo.entity

resultType="Student"

resultType="com.demo.entity.Student"

create_time

private Date createTime;

map-underscore-to-camel-case:true

@SpringBootApplication
@MapperScan("com.demo.mapper")
public class Application {
    public static void main(String[] args){
        SpringApplication.run(
            Application.class,args
        );
    }
}

@Mapper
public interface StudentMapper{
}

@Mapper
public interface StudentMapper{
}

@MapperScan

CREATE TABLE student
(
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50),
    age INT,
    gender VARCHAR(10),
    birthday DATE,
    create_time DATETIME
);

INSERT INTO student
(name,age,gender,birthday,create_time)
VALUES
('Tom',18,'M','2005-01-01',now()),
('Jack',20,'M','2003-01-01',now()),
('Lucy',19,'F','2004-01-01',now());

@Data
public class Student {
    private Long id;
    private String name;
    private Integer age;
    private String gender;
    private Date birthday;
    private Date createTime;
}

@Mapper
public interface StudentMapper {
    Student selectById(Long id);
}

<?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.demo.mapper.StudentMapper">
<select id="selectById"
        parameterType="java.lang.Long"
        resultType="com.demo.entity.Student">
    select
        id,
        name,
        age,
        gender,
        birthday,
        create_time
    from student
    where id=#{id}
</select>
</mapper>

Student selectById(Long id);

where id=#{id}

#{id}

方法参数

Student query(
    String name,
    Integer age
);

select *
from student
where name=#{name}
and age=#{age}

Parameter 'name' not found

第一个参数叫什么
第二个参数叫什么

arg0
arg1
param1
param2

Student query(
    @Param("name")
    String name,
    @Param("age")
    Integer age
);

where name=#{name}
and age=#{age}

Student query(Student student);

#{name}
#{age}

parameterType
resultType

Controller
    ↓
Service
    ↓
Mapper 方法参数
    ↓
parameterType
    ↓
SQL执行
    ↓
数据库结果
    ↓
resultType
    ↓
Java对象

Student selectById(Long id);

<select id="selectById"
        parameterType="java.lang.Long">
    select *
    from student
    where id=#{id}
</select>

parameterType="java.lang.Long"

List<Student> selectByName(String name);

<select id="selectByName"
        parameterType="java.lang.String">
select *
from student
where name=#{name}
</select>

studentMapper.selectByName("Tom");

select *
from student
where name='Tom'

@Data
public class StudentQuery {
    private String name;
    private Integer minAge;
    private Integer maxAge;
    private Date startBirthday;
    private Date endBirthday;
}

List<Student> query(StudentQuery query);

<select id="query"
parameterType="com.demo.entity.StudentQuery">
select *
from student
where name=#{name}
</select>

query.getName()

select *
from student
where id=1

resultType="com.demo.entity.Student"

Student student=new Student();
student.setId(1);
student.setName("Tom");
student.setAge(18);

数据库字段
      |
      |
Java属性

create_time

private Date createTime;

mybatis:
 configuration:
   map-underscore-to-camel-case:true

create_time
↓
createTime

student_name

private String name;

<resultMap id="studentMap"
           type="com.demo.entity.Student">
    <id column="id"
        property="id"/>
    <result column="student_name"
            property="name"/>
</resultMap>

<select id="select"
resultMap="studentMap">
select
id,
student_name
from student
</select>

where name='Tom'

查询全部

List<Student> query(Student student);

<select id="query"
        resultType="Student">
select *
from student
where 1=1
<if test="name != null">
and name=#{name}
</if>
</select>

<if test="name != null">
</if>

name=""

<if test="name != null 
      and name != ''">
and name=#{name}
</if>

name存在
并且
name不是空字符串

<select>
select *
from student
<if test="name!=null">
and name=#{name}
</if>
</select>

select *
from student
and name='Tom'

<select id="query"
resultType="Student">
select *
from student
<where>
<if test="name!=null and name!=''">
and name=#{name}
</if>
<if test="age!=null">
and age=#{age}
</if>
</where>
</select>

name="Tom"
age=null

select *
from student
where name='Tom'

name=null
age=18

select *
from student
where age=18

<where>
...
</where>

<trim
prefix="where"
prefixOverrides="and|or">
</trim>

<trim prefix="where"
      prefixOverrides="and|or">
<if test="name!=null">
and name=#{name}
</if>
</trim>

@Data
public class Student {
private String name;
private Integer age;
}

<insert id="insert">
insert into student
<trim prefix="("
       suffix=")"
       suffixOverrides=",">
<if test="name!=null">
name,
</if>
<if test="age!=null">
age,
</if>
</trim>
values
<trim prefix="("
       suffix=")"
       suffixOverrides=",">
<if test="name!=null">
#{name},
</if>
<if test="age!=null">
#{age},
</if>
</trim>
</insert>

name="Tom"
age=null

insert into student
(
name
)
values
(
'Tom'
)

update student
set
name=?,
age=?

update student
set
name=?,
where id=?

<update id="update">
update student
<set>
<if test="name!=null">
name=#{name},
</if>
<if test="age!=null">
age=#{age},
</if>
</set>
where id=#{id}
</update>

List<Student> selectByIds(
    @Param("ids")
    List<Long> ids
);

<select id="selectByIds">
select *
from student
where id in
<foreach collection="ids"
item="id"
open="("
close=")"
separator=",">
#{id}
</foreach>
</select>

Arrays.asList(1L,2L,3L)

where id in
(1,2,3)

int insert(Student student);

<insert id="insert">
insert into student
(
name,
age,
gender,
birthday
)
values
(
#{name},
#{age},
#{gender},
#{birthday}
)
</insert>

Student student=new Student();
student.setName("Tom");
student.setAge(null);

insert into student
(name)
values
('Tom')

<insert id="insertSelective">
insert into student
<trim prefix="("
       suffix=")"
       suffixOverrides=",">
<if test="name!=null">
name,
</if>
<if test="age!=null">
age,
</if>
<if test="gender!=null">
gender,
</if>
<if test="birthday!=null">
birthday,
</if>
</trim>
values
<trim prefix="("
       suffix=")"
       suffixOverrides=",">
<if test="name!=null">
#{name},
</if>
<if test="age!=null">
#{age},
</if>
<if test="gender!=null">
#{gender},
</if>
<if test="birthday!=null">
#{birthday},
</if>
</trim>
</insert>

id
username
password
nickname
avatar
email
phone
address
create_time
update_time

insertSelective

CREATE TABLE student
(
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50),
    age INT,
    gender VARCHAR(10),
    birthday DATE
);

@Data
public class Student {
    private Long id;
    private String name;
    private Integer age;
    private String gender;
    private Date birthday;
}

int batchInsert(
    @Param("list")
    List<Student> list
);

<insert id="batchInsert">
insert into student
(
name,
age,
gender,
birthday
)
values
<foreach collection="list"
         item="item"
         separator=",">
(
#{item.name},
#{item.age},
#{item.gender},
#{item.birthday}
)
</foreach>
</insert>

List<Student> list = new ArrayList<>();
Student s1=new Student();
s1.setName("Tom");
s1.setAge(18);
Student s2=new Student();
s2.setName("Jack");
s2.setAge(20);
studentMapper.batchInsert(list);

insert into student
(
name,
age
)
values
('Tom',18),
('Jack',20)

for(Student s:list){
    insert(s);
}

1000次SQL

insert into student values
(),
(),
()

1次SQL

应用
  |
  |
数据库

100000条数据

insert into student values
(...),
(...),
(...)

max_allowed_packet

500~1000条一次

List<List<Student>>
分批:
500条
500条
500条

insertSelective
batchInsert

Student student=new Student();
student.setName("Tom");
student.setAge(null);

insert into student
(
name
)
values
(
'Tom'
)

<insert id="insertSelective">
insert into student
<trim prefix="("
       suffix=")"
       suffixOverrides=",">
<if test="name!=null">
name,
</if>
<if test="age!=null">
age,
</if>
</trim>
values
<trim prefix="("
       suffix=")"
       suffixOverrides=",">
<if test="name!=null">
#{name},
</if>
<if test="age!=null">
#{age},
</if>
</trim>
</insert>

List<Student>

insert into student
values
(),
(),
()

ON DUPLICATE KEY UPDATE

CREATE TABLE user
(
id bigint primary key,
username varchar(50) unique,
age int
);

insert into user
(username,age)
values
('Tom',18);

insert into user
(username,age)
values
('Tom',20)
ON DUPLICATE KEY UPDATE
age=20;

username=Tom
违反唯一索引

update user
set age=20
where username='Tom'

int insertOrUpdate(Student student);

<insert id="insertOrUpdate">
insert into student
(
id,
name,
age,
gender
)
values
(
#{id},
#{name},
#{age},
#{gender}
)
ON DUPLICATE KEY UPDATE
name=#{name},
age=#{age},
gender=#{gender}
</insert>

供应商订单

先查询
再判断
再新增/修改

int batchUpdate(
    @Param("list")
    List<Student> list
);

<update id="batchUpdate">
<foreach collection="list"
         item="item"
         separator=";">
update student
set
name=#{item.name},
age=#{item.age}
where id=#{item.id}
</foreach>
</update>

update student
set name='Tom'
where id=1;
update student
set name='Jack'
where id=2;

id=1 修改 Tom
id=2 修改 Jack
id=3 修改 Lucy

update student
set name =
case id
when 1 then 'Tom'
when 2 then 'Jack'
when 3 then 'Lucy'
end
where id in(1,2,3);

<update id="batchUpdate">
update student
set name =
case id
<foreach collection="list"
item="item">
when #{item.id}
then #{item.name}
</foreach>
end
where id in
<foreach collection="list"
item="item"
open="("
close=")"
separator=",">
#{item.id}
</foreach>
</update>

foreach

CASE WHEN

@Data
public class StudentQuery {
    /**
     * 开始日期
     */
    private Date startBirthday;
    /**
     * 结束日期
     */
    private Date endBirthday;
    private String gender;
}

List<Student> queryStudent(
        @Param("query")
        StudentQuery query,
        @Param("name")
        String name,
        @Param("ids")
        List<Long> ids,
        @Param("age")
        Integer age,
        @Param("limit")
        Integer limit
);

query
name
ids
age
limit

<select id="queryStudent"
resultType="Student">
select
id,
name,
age,
gender,
birthday,
create_time
from student
<where>
<!-- 对象参数 -->
<if test="query.startBirthday != null">
and birthday >= #{query.startBirthday}
</if>
<if test="query.endBirthday != null">
and birthday <= #{query.endBirthday}
</if>
<!-- String参数 -->
<if test="name != null 
          and name != ''">
and name=#{name}
</if>
<!-- Integer参数 -->
<if test="age != null">
and age=#{age}
</if>
<!-- List参数 -->
<if test="ids != null 
          and ids.size()>0">
and id in
<foreach collection="ids"
item="id"
open="("
close=")"
separator=",">
#{id}
</foreach>
</if>
</where>
limit #{limit}
</select>

StudentQuery query=new StudentQuery();
query.setStartBirthday(
    new Date()
);
mapper.queryStudent(
query,
"Tom",
Arrays.asList(1L,2L),
18,
10
);

select *
from student
where
birthday >= ?
and name='Tom'
and age=18
and id in(1,2)
limit 10

Student queryOne(
@Param("query")
StudentQuery query,
@Param("name")
String name
);

<select id="queryOne"
resultType="Student">
select *
from student
where name=#{name}
limit 1
</select>

Student student;

select
id,
name,
age,
gender,
birthday,
create_time
from student

<sql>

<sql id="studentColumns">
id,
name,
age,
gender,
birthday,
create_time
</sql>

<select id="selectList"
resultType="Student">
select
<include refid="studentColumns"/>
from student
</select>

select
id,
name,
age,
gender,
birthday,
create_time
from student

Base_Column_List

<sql id="Base_Column_List">
id,
order_no,
status,
create_time
</sql>

order_info

order_info_202601
order_info_202602
order_info_202603
...

order_info

2024年  5000万
2025年  8000万
2026年  1亿

select *
from order_info
where order_no='10001'

where create_time >= today

5年前订单

order_info_202601

CREATE TABLE order_info_202601
(
    id BIGINT PRIMARY KEY,
    order_no VARCHAR(64),
    user_id BIGINT,
    amount DECIMAL(10,2),
    status VARCHAR(20),
    create_time DATETIME
);

order_info_202602
order_info_202603

select *
from order_info

select *
from order_info_202601

from #{tableName}

from ?

${}

<select id="selectOrder">
select *
from ${tableName}
where order_no=#{orderNo}
</select>

where id=#{id}

where id=?

PreparedStatement

from ${tableName}

from order_info_202601

public interface OrderMapper {
    List<OrderInfo> selectByOrderNo(
        @Param("tableName")
        String tableName,
        @Param("orderNo")
        String orderNo
    );
}

<select id="selectByOrderNo"
        resultType="OrderInfo">
select
id,
order_no,
user_id,
amount,
status,
create_time
from ${tableName}
where order_no=#{orderNo}
</select>

String tableName =
"order_info_202601";
orderMapper.selectByOrderNo(
    tableName,
    "ORDER001"
);

select *
from order_info_202601
where order_no='ORDER001'

${}

String tableName=request.getParameter();

order_info where 1=1

from order_info where 1=1

public String getOrderTableName(LocalDate date){
    String month =
        date.format(
            DateTimeFormatter.ofPattern("yyyyMM")
        );
    return "order_info_"+month;
}

order_info_202601
order_info_202602

int insertOrder(
@Param("tableName")
String tableName,
@Param("order")
OrderInfo order
);

<insert id="insertOrder">
insert into ${tableName}
(
id,
order_no,
user_id,
amount,
status,
create_time
)
values
(
#{order.id},
#{order.orderNo},
#{order.userId},
#{order.amount},
#{order.status},
#{order.createTime}
)
</insert>

<select id="selectOrder">
select *
from ${tableName}
where order_no=#{orderNo}
</select>

int deleteOrder(
@Param("tableName")
String tableName,
@Param("id")
Long id
);

<delete id="deleteOrder">
delete from ${tableName}
where id=#{id}
</delete>

<update id="updateOrder">
update ${tableName}
<set>
<if test="order.status!=null">
status=#{order.status},
</if>
<if test="order.amount!=null">
amount=#{order.amount},
</if>
</set>
where id=#{order.id}
</update>

order_detail

id
order_id
product_id
quantity
price

@Data
public class OrderDetail {
private Long id;
private Long orderId;
private Long productId;
private Integer quantity;
private BigDecimal price;
}

int batchInsert(
@Param("list")
List<OrderDetail> list
);

<insert id="batchInsert">
insert into order_detail
(
id,
order_id,
product_id,
quantity,
price
)
values
<foreach collection="list"
item="item"
separator=",">
(
#{item.id},
#{item.orderId},
#{item.productId},
#{item.quantity},
#{item.price}
)
</foreach>
</insert>

insert into order_detail
values
(1,100,1,2,20),
(2,100,2,1,50),
(3,100,3,5,10)

SqlSession session;
StudentMapper mapper =
session.getMapper(StudentMapper.class);
mapper.selectById(1);
mapper.selectById(1);

select *
from student
where id=1

SqlSession

SqlSession1
缓存存在
关闭
缓存消失

session1
session2

mapper.update();

sqlSession.clearCache();

SqlSession1
       |
       |
 Mapper二级缓存
       |
       |
SqlSession2

<cache/>

<mapper namespace="StudentMapper">
<cache/>
</mapper>

public class Student
implements Serializable{
}

city

order

mybatis:
  configuration:
    log-impl:
      org.apache.ibatis.logging.stdout.StdOutImpl

Preparing:
select *
from student
where id=?
Parameters:
1(Long)

slf4j

mybatis:
 configuration:
  log-impl:
   org.apache.ibatis.logging.slf4j.Slf4jImpl

<foreach collection="ids">

ids=null

where id in ()

<if test="ids!=null and ids.size()>0">
</if>

where name='${name}'

Tom' or '1'='1

where name='Tom'
or
'1'='1'

where name=#{name}

select *
from order
limit 1000000,20

1000020条

select id
from order
limit 1000000,20

where id > lastId
limit 20

select *
from student

select
id,
name,
age
from student

<

<

>

>

birthday <= #{date}

birthday <= #{date}

select
query
find

insert

update

delete

StudentMapper.xml
10000行

student
order
invoice

batchInsert(1000000)

500条
1000条
提交一次

几十层 if