Java：MybatisPlus--条件构造器

1、条件构造器类别

①wrapper：抽象类，条件类的顶层，提供了一些获取和判断相关的方法。

②AbstractWrapper：抽象类，Wrapper的子类，提供了所有的条件相关方法。

③AbstractLambdaWrapper：抽象类，AbstractWrapper的子类，确定字段参数为方法引用类型

④QueryWrapper：AbstractWrapper的子类，如果需要传递String类型的字段信息，创建该对象

⑤LambdaQueryWrapper：AbstractLambdaWrapper的子类，如果我们需要传递方法引用方式的字段信息，创建该对象。

 2、等值查询

测试：eq

@Test
void eq(){//1.创建QueryWrapper对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定String字段名称和值lambdaQueryWrapper.eq(User::getName,"Jack");//3.使用条件完成查询User user = userMapper.selectOne(lambdaQueryWrapper);System.out.println(user);
}

测试：allEq

@Test
void allEq(){LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();lambdaQueryWrapper.eq(User::getName,"Jone");lambdaQueryWrapper.eq(User::getAge,18);User user = userMapper.selectOne(lambdaQueryWrapper);System.out.println(user);
}

测试：ne

@Test
void ne(){//1.创建QueryWrapper对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定String字段名称和值String name = "Jone";lambdaQueryWrapper.ne(User::getName,name);//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

3、范围查询

gt    lt

@Test
void gt(){//1.创建QueryWrapper对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定字段名称和值Integer age = 18;lambdaQueryWrapper.gt(User::getAge,age);//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

ge    le

@Test
void ge(){//1.创建QueryWrapper对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定字段名称和值Integer age = 18;lambdaQueryWrapper.ge(User::getAge,age);//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

between    notBetween

@Test
void between(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定字段名称和值lambdaQueryWrapper.between(User::getAge,18,30);//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

4、模糊查询

like、notLike、likeLeft、likeRight

@Test
void like(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定字段名称和值lambdaQueryWrapper.like(User::getName,"J");//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

5、判空查询

@Test
void isNull(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定字段名称lambdaQueryWrapper.isNull(User::getName);//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

@Test
void in(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定字段名称和值ArrayList<Integer> arrayList = new ArrayList<>();Collections.addAll(arrayList,18,20,21);lambdaQueryWrapper.in(User::getAge,arrayList);//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

@Test
void groupBy(){//1.创建 QueryWrapper 对象QueryWrapper<User> queryWrapper = new QueryWrapper<>();//2.设置条件，指定字段名称和值queryWrapper.groupBy("age");queryWrapper.select("age,count(*) as field_count");//3.使用条件完成查询List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);System.out.println(maps);
}

@Test
void having(){QueryWrapper<User> queryWrapper = new QueryWrapper<>();//分组字段queryWrapper.groupBy("age");//查询字段queryWrapper.select("age,count(*) as field_count");//聚合条件筛选queryWrapper.having("field_count = 1");List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);System.out.println(maps);
}

@Test
void orderBy(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.设置条件，指定降序排序字段lambdaQueryWrapper.orderBy(true,true,User::getId);lambdaQueryWrapper.orderBy(true,false,User::getAge);//3.使用条件完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

@Test
void nested(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.构建条件查询语句lambdaQueryWrapper.nested(i -> i.eq(User::getName, "Billie").ne(User::getAge,22));//3.完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

@Test
void apply(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.构建条件查询语句lambdaQueryWrapper.apply("id = 1");//3.完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

@Test
void last(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.构建条件查询语句lambdaQueryWrapper.last("limit 0,2");//3.完成查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

@Test
void exists(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.构建查询条件lambdaQueryWrapper.exists("select id from powershop_user where age = 18");//3.查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}

@Test
void select(){//1.创建 QueryWrapper 对象LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();//2.构建查询条件lambdaQueryWrapper.select(User::getId,User::getName);//3.查询List<User> users = userMapper.selectList(lambdaQueryWrapper);System.out.println(users);
}