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=?
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//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=?
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//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(); |
