SpringBoot入门教程06——整合mybatis-plus(二)

大纲

springboot整合mybatis-plus入门，以及mybatis-plus代码生成工具入门,传送门
事务控制
分页
自定义SQL
条件构造器Wrapper入门

事务控制

在springboot启动类上加@EnableTransactionManagement注解
在要做事务控制的类或者方法上加@Transactional注解

来个例子，在UserController中增加如下代码

@Transactional
@RequestMapping("/addError")
public Object addEoor(){
    
    
    Random random = new Random();
    User user = new User();
    user.setName("zzz"+random.nextInt(100));
    user.setAge(random.nextInt(100));
    userMapper.insert(user);
    int k=2/0;
    user = new User();
    user.setName("kkk"+random.nextInt(100));
    user.setAge(random.nextInt(100));
    userMapper.insert(user);

    return user;
}

重启应用，打开浏览器打开浏览器输入http://127.0.0.1:8080/user/addError，会发现2条数据都没有插入数据库，而如果把@Transactional注释掉，再刷新浏览器，会发现第一条数据成功插入到数据库中

补充一点，启动类不加@EnableTransactionManagement注解，只有@Transactional注解事务也会生效

分页

分页的实现非常简单，只需要在应用启动时，向spring容器注入分页拦截器PaginationInterceptor的实例即可

代码如下：

@Configuration
public class MybatisPlusConfig {
    
    

    @Bean
    public PaginationInterceptor paginationInterceptor() {
    
    
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        // 设置请求的页面大于最大页后操作， true调回到首页，false 继续请求  默认false
        // paginationInterceptor.setOverflow(false);
        // 设置最大单页限制数量，默认 500 条，-1 不受限制
        // paginationInterceptor.setLimit(500);
        // 开启 count 的 join 优化,只针对部分 left join
        paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true));
        return paginationInterceptor;
    }
}

然后在查询的时候传入Page对象即可实现分页查询，UserController加入如下代码

@RequestMapping("/page")
public Object page(@RequestParam(value = "pageNum",defaultValue = "1") Integer pageNum,@RequestParam(defaultValue = "2") Integer pageSize){
    
    
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    Page<User> page = new Page(pageNum,pageSize);
    Page<User> userPage = userMapper.selectPage(page, wrapper);
    return userPage;
}

自定义SQL

尽管mybatis-plus给我们提供了强大的条件构造器Wrapper，支持常见的CRUD操作，但是实际开发中仍避免不了要手动写sql。比如现在要查user表id为偶数的数据，实现方式有以下几种

@Select注解实现
xml文件实现
基于@Select注解或者xml文件，使用Wrapper辅助实现

直接上代码，先来UserMapper

List<User> selectListByEvenId();

@Select("select * from user where id%2=1")
List<User> selectListByOddId();

@Select("select * from user ${ew.customSqlSegment}")
List<User> selectAll(@Param(Constants.WRAPPER) Wrapper wrapper);

UserMapper.xml

<select id="selectListByEvenId" resultType="com.henry.entity.User">
   SELECT * FROM user where id%2=0
</select>

UserController

@RequestMapping("/even")
public Object even(){
    
    
    List<User> userList = userMapper.selectListByEvenId();
    return userList;
}

@RequestMapping("/odd")
public Object odd(){
    
    
    List<User> userList = userMapper.selectListByOddId();
    return userList;
}

@RequestMapping("/selectAll")
public Object selectAll(){
    
    
    List<User> userList = userMapper.selectAll(new QueryWrapper());
    return userList;
}

代码一看就能明白，这里说一下几个可能遇到的坑

扫描二维码关注公众号，回复： 12593005 查看本文章

使用Wrapper辅助实现sql时，如果传的Wrapper实例是null，会报空指针错误，可以按照selectAll方法中的写法规避
如果mapper.xml和mapper接口都放在com.xxx.mapper包下，调用even()方法时会报sql没绑定的错误，此时需要修改一下pom文件，支持编译xml文件

pom文件修改如下

<build>
   <resources>
      <resource>
         <directory>src/main/resources</directory>
         <filtering>true</filtering>
      </resource>
      <resource>
         <directory>src/main/java</directory>
         <includes>
            <include>**/*.xml</include>
            <include>**/*.json</include>
         </includes>
      </resource>
   </resources>
   <plugins>
      <plugin>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
   </plugins>
</build>

条件构造器Wrapper

条件构造器Wrapper是mybatis-plus抽象出来用来生成sql语句片段的接口，Wrapper接口支持在不写sql语句的情况下，自动生成sql语句对数据库表进行增删改查，包括一些比较复杂的条件查询。

我们先看一下Wrapper接口的类图
在这里插入图片描述

顶层接口Wrapper,然后有2个抽象类AbstractWrapper和AbstractChainWrapper继承Wrapper接口，其中AbstractChainWrapper算是AbstractWrapper使用装饰着模式创建出来的一个类，其wrapperChildren属性是通过构造函数传入的AbstractWrapper实现类的实例。

了解装饰者设计模式的同学应该知道

装饰者模式的主要作用是给一个类添加新功能
主要实现方式：装饰类和被装饰类实现相同接口，然后装饰类通过构造函数传入被装饰类，装饰类的接口实现全部通过被装饰类实例方法实现，可以在方法中做增强

所以我们先看AbstractWrapper类，AbstractWrapper类中方法很多，基本上见名知义

allEq

allEq(Map<R, V> params)
allEq(Map<R, V> params, boolean null2IsNull)
allEq(boolean condition, Map<R, V> params, boolean null2IsNull)

参数说明:

params : key为数据库字段名,value为字段值
null2IsNull : 为true则在map的value为null时调用 isNull 方法,为false时则忽略value为null的

condition:为true时才生成sql片段

例1: allEq({id:1,name:"老王",age:null})—>id = 1 and name = '老王' and age is null
例2: allEq({id:1,name:"老王",age:null}, false)—>id = 1 and name = '老王'

eq

eq(R column, Object val)
eq(boolean condition, R column, Object val)

等于 =
例: eq("name", "老王")—>name = '老王'

ne

ne(R column, Object val)
ne(boolean condition, R column, Object val)

不等于 <>
例: ne("name", "老王")—>name <> '老王'

gt

gt(R column, Object val)
gt(boolean condition, R column, Object val)

大于 >
例: gt("age", 18)—>age > 18

ge

ge(R column, Object val)
ge(boolean condition, R column, Object val)

大于等于 >=
例: ge("age", 18)—>age >= 18

lt

lt(R column, Object val)
lt(boolean condition, R column, Object val)

小于 <
例: lt("age", 18)—>age < 18

le

le(R column, Object val)
le(boolean condition, R column, Object val)

小于等于 <=
例: le("age", 18)—>age <= 18

between

between(R column, Object val1, Object val2)
between(boolean condition, R column, Object val1, Object val2)

BETWEEN 值1 AND 值2
例: between("age", 18, 30)—>age between 18 and 30

notBetween

notBetween(R column, Object val1, Object val2)
notBetween(boolean condition, R column, Object val1, Object val2)

NOT BETWEEN 值1 AND 值2
例: notBetween("age", 18, 30)—>age not between 18 and 30

like

like(R column, Object val)
like(boolean condition, R column, Object val)

LIKE ‘%值%’
例: like("name", "王")—>name like '%王%'

notLike

notLike(R column, Object val)
notLike(boolean condition, R column, Object val)

NOT LIKE ‘%值%’
例: notLike("name", "王")—>name not like '%王%'

likeLeft

likeLeft(R column, Object val)
likeLeft(boolean condition, R column, Object val)

LIKE ‘%值’
例: likeLeft("name", "王")—>name like '%王'

likeRight

likeRight(R column, Object val)
likeRight(boolean condition, R column, Object val)

LIKE ‘值%’
例: likeRight("name", "王")—>name like '王%'

isNull

isNull(R column)
isNull(boolean condition, R column)

字段 IS NULL
例: isNull("name")—>name is null

isNotNull

isNotNull(R column)
isNotNull(boolean condition, R column)

字段 IS NOT NULL
例: isNotNull("name")—>name is not null

in

in(R column, Collection<?> value)
in(boolean condition, R column, Collection<?> value)

字段 IN (value.get(0), value.get(1), …)
例: in("age",{1,2,3})—>age in (1,2,3)

in(R column, Object... values)
in(boolean condition, R column, Object... values)

字段 IN (v0, v1, …)
例: in("age", 1, 2, 3)—>age in (1,2,3)

notIn

notIn(R column, Collection<?> value)
notIn(boolean condition, R column, Collection<?> value)

字段 NOT IN (value.get(0), value.get(1), …)
例: notIn("age",{1,2,3})—>age not in (1,2,3)

notIn(R column, Object... values)
notIn(boolean condition, R column, Object... values)

字段 NOT IN (v0, v1, …)
例: notIn("age", 1, 2, 3)—>age not in (1,2,3)

inSql

inSql(R column, String inValue)
inSql(boolean condition, R column, String inValue)

字段 IN ( sql语句 )
例: inSql("age", "1,2,3,4,5,6")—>age in (1,2,3,4,5,6)
例: inSql("id", "select id from table where id < 3")—>id in (select id from table where id < 3)

notInSql

notInSql(R column, String inValue)
notInSql(boolean condition, R column, String inValue)

字段 NOT IN ( sql语句 )
例: notInSql("age", "1,2,3,4,5,6")—>age not in (1,2,3,4,5,6)
例: notInSql("id", "select id from table where id < 3")—>id not in (select id from table where id < 3)

groupBy

groupBy(R... columns)
groupBy(boolean condition, R... columns)

分组：GROUP BY 字段, …
例: groupBy("id", "name")—>group by id,name

orderByAsc

orderByAsc(R... columns)
orderByAsc(boolean condition, R... columns)

排序：ORDER BY 字段, … ASC
例: orderByAsc("id", "name")—>order by id ASC,name ASC

orderByDesc

orderByDesc(R... columns)
orderByDesc(boolean condition, R... columns)

排序：ORDER BY 字段, … DESC
例: orderByDesc("id", "name")—>order by id DESC,name DESC

orderBy

orderBy(boolean condition, boolean isAsc, R... columns)

排序：ORDER BY 字段, …
例: orderBy(true, true, "id", "name")—>order by id ASC,name ASC

having

having(String sqlHaving, Object... params)
having(boolean condition, String sqlHaving, Object... params)

HAVING ( sql语句 )
例: having("sum(age) > 10")—>having sum(age) > 10
例: having("sum(age) > {0}", 11)—>having sum(age) > 11

or

or()
or(boolean condition)

拼接 OR

注意事项:

主动调用or表示紧接着下一个方法不是用and连接!(不调用or则默认为使用and连接)

例: eq("id",1).or().eq("name","老王")—>id = 1 or name = '老王'

or(Consumer<Param> consumer)
or(boolean condition, Consumer<Param> consumer)

OR 嵌套
例: or(i -> i.eq("name", "李白").ne("status", "活着"))—>or (name = '李白' and status <> '活着')

and

and(Consumer<Param> consumer)
and(boolean condition, Consumer<Param> consumer)

AND 嵌套
例: and(i -> i.eq("name", "李白").ne("status", "活着"))—>and (name = '李白' and status <> '活着')

nested

nested(Consumer<Param> consumer)
nested(boolean condition, Consumer<Param> consumer)

正常嵌套不带 AND 或者 OR
例: nested(i -> i.eq("name", "李白").ne("status", "活着"))—>(name = '李白' and status <> '活着')

apply

apply(String applySql, Object... params)
apply(boolean condition, String applySql, Object... params)

拼接 sql

注意事项:

该方法可用于数据库函数动态入参的params对应前面applySql内部的{index}部分.这样是不会有sql注入风险的,反之会有!

例: apply("id = 1")—>id = 1
例: apply("date_format(dateColumn,'%Y-%m-%d') = '2008-08-08'")—>date_format(dateColumn,'%Y-%m-%d') = '2008-08-08'")
例: apply("date_format(dateColumn,'%Y-%m-%d') = {0}", "2008-08-08")—>date_format(dateColumn,'%Y-%m-%d') = '2008-08-08'")

last

last(String lastSql)
last(boolean condition, String lastSql)

无视优化规则直接拼接到 sql 的最后

注意事项:

只能调用一次,多次调用以最后一次为准有sql注入的风险,请谨慎使用

例: last("limit 1")

exists

exists(String existsSql)
exists(boolean condition, String existsSql)

拼接 EXISTS ( sql语句 )
例: exists("select id from table where age = 1")—>exists (select id from table where age = 1)

notExists

notExists(String notExistsSql)
notExists(boolean condition, String notExistsSql)

拼接 NOT EXISTS ( sql语句 )
例: notExists("select id from table where age = 1")—>not exists (select id from table where age = 1)