Mybatis-Plus 条件构造器
Mybatis-Plus是一个MyBatis的增强工具，在Mybatis-Plus的基础上只做增强不做改变，为简化开发、提高效率而生。
Mybatis-Plus的核心功能之一是条件构造器，通过条件构造器，我们在单表的增删改查的所有操作都不需要写SQL。
1、Wrapper
Mybatis Plus 提供的几种条件构造器，关系如下：
2、语法详情
方法名 |
说明 |
用法实例 |
等价SQL |
allEq(Map |
全部等于 |
allEq({id:1,name:"老王"}) |
id = 1 and name = '老王' |
eq(R column, Object val) |
等于 = |
eq("name", "老王") |
name = '老王' |
ne(R column, Object val) |
不等于 <> |
ne("name", "老王") |
name <> '老王' |
gt(R column, Object val) |
大于 > |
gt("age", 18) |
age > 18 |
ge(R column, Object val) |
大于等于 >= |
ge("age", 18) |
age >= 18 |
lt(R column, Object val) |
小于 < |
lt("age", 18) |
age < 18 |
le(R column, Object val) |
小于等于 <= |
le("age", 18) |
age <= 18 |
between(R column, Object val1, Object val2) |
BETWEEN 值1 AND 值2 |
between("age", 18, 30) |
age between 18 and 30 |
notBetween(R column, Object val1, Object val2) |
NOT BETWEEN 值1 AND 值2 |
notBetween("age", 18, 30) |
age not between 18 and 30 |
like(R column, Object val) |
LIKE '%值%' |
like("name", "王") |
name like '%王%' |
notLike(R column, Object val) |
NOT LIKE '%值%' |
notLike("name", "王") |
name not like '%王%' |
likeLeft(R column, Object val) |
LIKE '%值' |
likeLeft("name", "王") |
name like '%王' |
likeRight(R column, Object val) |
LIKE '值%' |
likeRight("name", "王") |
name like '王%' |
notLikeLeft(R column, Object val) |
NOT LIKE '%值' |
notLikeLeft("name", "王") |
name not like '%王' |
notLikeRight(R column, Object val) |
NOT LIKE '值%' |
notLikeRight("name", "王") |
name not like '王%' |
isNull(R column) |
字段 IS NULL |
isNull("name") |
name is null |
isNotNull(R column) |
字段 IS NOT NULL |
isNotNull("name") |
name is not null |
in(R column, Collection value) |
字段 IN (value.get(0), value.get(1), ...) |
in("age",{1,2,3}) |
age in (1,2,3) |
notIn(R column, Collection value) |
字段 NOT IN (value.get(0), value.get(1), ...) |
notIn("age",{1,2,3}) |
age not in (1,2,3) |
inSql(R column, String inValue) |
字段 IN ( sql语句 ) |
inSql("id", "select id from table where id < 3") |
id in (select id from table where id < 3) |
notInSql(R column, String inValue) |
字段 NOT IN ( sql语句 ) |
notInSql("id", "select id from table where id < 3") |
id not in (select id from table where id < 3) |
groupBy(R... columns) |
分组：GROUP BY 字段, ... |
groupBy("id", "name") |
group by id,name |
orderByAsc(R... columns) |
排序：ORDER BY 字段, ... ASC |
orderByAsc("id", "name") |
order by id ASC,name ASC |
orderByDesc(R... columns) |
排序：ORDER BY 字段, ... DESC |
orderByDesc("id", "name") |
order by id DESC,name DESC |
orderBy(boolean condition, boolean isAsc, R... columns) |
排序：ORDER BY 字段, ... |
orderBy(true, true, "id", "name") |
order by id ASC,name ASC |
having(String sqlHaving, Object... params) |
HAVING ( sql语句 ) |
having("sum(age) > 10") having("sum(age) > {0}", 11) |
having sum(age) > 10 having sum(age) > 11 |
func(Consumer |
func 方法(主要方便在出现if...else下调用不同方法能不断链) |
func(i -> if(true) {i.eq("id", 1)} else {i.ne("id", 1)}) |
|
or() |
拼接 OR |
eq("id",1).or().eq("name","老王") |
id = 1 or name = '老王' |
or(Consumer consumer) |
OR 嵌套 |
or(i -> i.eq("name", "李白").ne("status", "活着")) |
or (name = '李白' and status <> '活着') |
and(Consumer consumer) |
AND 嵌套 |
and(i -> i.eq("name", "李白").ne("status", "活着")) |
and (name = '李白' and status <> '活着') |
nested(Consumer consumer) |
正常嵌套 不带 AND 或者 OR |
nested(i -> i.eq("name", "李白").ne("status", "活着")) |
(name = '李白' and status <> '活着') |
apply(String applySql, Object... params) |
拼接 sql(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!) |
apply("date_format(dateColumn,'%Y-%m-%d') = '2008-08-08'") |
date_format(dateColumn,'%Y-%m-%d') = '2008-08-08'") |
last(String lastSql) |
无视优化规则直接拼接到 sql 的最后(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) |
last("limit 1") |
|
exists(String existsSql) |
拼接 EXISTS ( sql语句 ) |
exists("select id from table where age = 1") |
exists (select id from table where age = 1) |
notExists(String notExistsSql) |
拼接 NOT EXISTS ( sql语句 ) |
notExists("select id from table where age = 1") |
not exists (select id from table where age = 1) |
select(String... sqlSelect) |
设置查询字段 |
select("id", "name", "age") |
|
set(String column, Object val) |
SQL SET 字段 |
set("name", "老李头") |
|
setSql(String sql) |
设置 SET 部分 SQL |
setSql("name = '老李头'") |
3、具体使用
1.使用QueryWrapper和UpdateWrapper
/**
* 根据年龄查询
* @param age
* @return
*/
@PostMapping("selectByAge")
@ResponseBody
public AjaxResult selectByAge(@RequestBody String age){
//定义条件构造器
QueryWrapper qw = new QueryWrapper<>();
//构造条件构造器
qw.eq("age","18");
//查询
List result = aService.list(qw);
return AjaxResult.success(result);
}2.使用LambdaQueryWrapper和LambdaUpdateWrapper(推荐)
/**
* 根据年龄查询
* @param age
* @return
*/
@PostMapping("selectByAgeTwo")
@ResponseBody
public AjaxResult selectByAgeTwo(@RequestBody String age){
LambdaQueryWrapper lqw = new LambdaQueryWrapper().eq(A::getAge,age);
List result = aService.list(lqw);
return AjaxResult.success(result);
}上面两种方法，推荐使用第二种，因为使用QueryWrapper或者UpdateWrapper时，对于条件的某个列，我们是写的字符串配置，比如 QueryWrapper.eq(“age”,18);这里的age是数据库表的列名，很有可能我们会写错，但是通过lambda 的方式，LambdaQueryWrapper.eq(User::getAge,18)，这样就不会有写错的可能了。所以推荐大家使用Lambda 的方式。