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Mybatis-Plus中and()和or()的使用与原理详解_mybatisplus and or

作者：AllinToyou | 2024-02-28 09:02:59

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mybatisplus and or

最近发现MyBatisPlus还是挺好用的,下面这篇文章主要给大家介绍了关于Mybatis-Plus中and()和or()的使用与原理的相关资料,文中通过实例代码介绍的非常详细,需要的朋友可以参考下

一. 简单无优先级连接(即无括号的sql语句)

简单来说,两个子条件间默认and与连接,若两个之间显式写出or()则or或连接.

1. 与连接 and()

当需要简单的将两个条件与连接,则最直接的写法为:

QueryWrapper<AttrEntity> queryWrapper = new QueryWrapper<AttrEntity>().

eq("attr_id",key).

eq("catelog_id",catelogId);

当然也可以显式地写出and()如下,但没必要:

QueryWrapper<AttrEntity> queryWrapper = new QueryWrapper<AttrEntity>().

eq("attr_id",key);

queryWrapper.and(qr -> qr.eq("catelog_id", catelogId));

2. 或连接 or()

当需要简单的将两个条件或连接,则最直接的写法为:

QueryWrapper<AttrEntity> queryWrapper = new QueryWrapper<AttrEntity>().

eq("attr_id",key).

or().

eq("catelog_id",catelogId);

当然也可以如下,但不那么直观:

QueryWrapper<AttrEntity> queryWrapper = new QueryWrapper<AttrEntity>().

eq("attr_id",key);

queryWrapper.or(qr -> qr.eq("catelog_id", catelogId));

二. 复杂有优先级的的连接

上面有2个不推荐的做法,是因为sql语句为A or B , A and B这种简单连接.当涉及到诸如 A and ( B or C) and D 这类的复杂有优先级的的连接,直接拼接会导致成为 A and B or C and D.所以这时候需要需要or(Consumer consumer),and(Consumer consumer)这两个方法.示例如下:

QueryWrapper<AttrEntity> queryWrapper = new QueryWrapper<AttrEntity>().eq("attr_type", "base".equalsIgnoreCase(type) ? 1 : 0);

queryWrapper.and(qr ->

qr.eq("attr_id", key).

or().

like("attr_name", key)

);

queryWrapper.and(qr -> qr.eq("catelog_id", catelogId));

生成的sql语句如下:

select ...

WHERE (attr_type = ? AND ( (attr_id = ? OR attr_name LIKE ?) ) AND ( (catelog_id = ?) ))

...;

由此还可见or(Consumer consumer),and(Consumer consumer)这两个方法参数为Consumer时,会在连接处生成2对括号,以此提高优先级.

补充：MybatisPlus中and和or的组合使用

案例1：where A=? and B=?

1 2	`//SELECT id,name,age,sex FROM student WHERE (name = ? AND age = ?)` `List<Student> list = studentService.lambdaQuery().eq(Student::getName,` `"1").eq(Student::getAge,` `1).list();`

案例2：where A=? or B=?

1 2	`//SELECT id,name,age,sex FROM student WHERE (name = ? OR age = ?)` `List<Student> list = studentService.lambdaQuery().eq(Student::getName,` `"1").or().eq(Student::getAge,` `12).list();`

案例3：where A=? or（C=? and D=?)

//SELECT id,name,age,sex FROM student WHERE (name = ? OR (name = ? AND age = ?))

List<Student> list =

studentService

.lambdaQuery()

.eq(Student::getName, "1")

.or(wp -> wp.eq(Student::getName, "1").eq(Student::getAge, 12))

.list();

案例4：where (A=?andB=?)or(C=?andD=?)

// SELECT id,name,age,sex FROM student WHERE ((name = ? AND age = ?) OR (name = ? AND age = ?))

List<Student> list =

studentService

.lambdaQuery()

.and(wp -> wp.eq(Student::getName, "1").eq(Student::getAge, 12))

.or(wp -> wp.eq(Student::getName, "1").eq(Student::getAge, 12))

.list();

案例5：whert A =? or (B=? and ( C=? or D=?))

// SELECT * FROM student WHERE ((name <> 1) OR (name = 1 AND (age IS NULL OR age >= 11)))

List<Student> list =

studentService

.lambdaQuery()

.and(wp -> wp.ne(Student::getName, "1"))

.or(

wp ->

wp.eq(Student::getName, "1")

.and(wpp -> wpp.isNull(Student::getAge).or().ge(Student::getAge, 11)))

.list();

来源：https://www.jb51.net/article/262039.htm

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