Mybatis-Plus中and()和or()的使用与原理详解

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)
  • 1. 与连接 and()
  • 2. 或连接 or()
• 二. 复杂有优先级的的连接
• 补充：MybatisPlus中and和or的组合使用
• 总结

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:

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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:

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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:

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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:

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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:

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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:

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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=?) 

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//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=?) 

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// 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=?)) 

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// 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