Wrapper 使用 lambda 形式可以通过方法引用的方式来使用实体字段名，避免直接写数据库表字段名时的错写名字。
一般的 QueryWrapper 写法：
List<User> userList = baseMapper.selectList(new QueryWrapper<User>().eq("user_id", userId));
需要手写数据库字段 user_id，容易出错，并且与数据库字段产生依赖。
lambda 的 QueryWrapper 写法：
List<User> userList = baseMapper.selectList(new QueryWrapper<User>().lambda().eq(User::getId, userId)));
直接调用类的 get 方法进行关联，有一定代码解耦效果。
List<User> userList = baseMapper.selectList(Wrappers.lambdaQuery(User.class).eq(User::getId, userId));
查一条数据：
User user = new LambdaQueryChainWrapper<>(baseMapper).eq(User::getId, userId).one();
查对象列表：
List<User> userList = new LambdaQueryChainWrapper<>(baseMapper).eq(User::getId, userId).list();
链式查询得到 list 对象列表，可读性没有 lambdaQuery 好。
| 函数 | 说明 | 例子 | 生成的sql语句 |
|---|---|---|---|
| eq | 等于 = | eq(“name”, “老王”) | name = ‘老王’ |
| ne | 不等于 <> | ne(“name”, ‘老王’ | name <> ‘老王’ |
| gt | 大于 > | gt(“age”, 18) | age > 18 |
| ge | 大于等于 >= | ge(“age”, 18) | age >= 18 |
| lt | 小于 < | lt(“age”, 18) | age < 18 |
| le | 小于等于 <= | le(“age”, 18) | age <= 18 |
| between | BETWEEN v1 AND v2 | between(“age”, 18, 24) | age between 18 and 24 |
| notBetween | NOT BETWEEN v1 AND v2 | notBetween(“age”，18，24) | age not between 18 and 24 |
| like | LIKE ‘%值%’ | like(“name”，“王”) | name like '%王%’ |
| notLike | NOT LIKE ‘%值%’ | notLike(“name”，“王”) | name not like '%王%’ |
| likeLeft | LIKE ‘%值’ | likeLeft(“name”，“王”) | name like '%王 |
| likeRight | LIKE ‘值%’ | likeRight (“name”，“王”) | name like '王%’ |
| isNull | 字段 IS NULL | isNull (“name”) | name is null |
| isNotNull | 字段 IS NOT NULL | isNotNull (“name”) | name is not null |
| in | 字段 IN (v1, v2, v3) | in(“age”，{1,2,3} ) | age in (1,2,3) |
| notIn | 字段 NOT IN (v1, v2, v3) | notIn(“age”, 1, 2, 3) | age not in (1, 2, 3) |
| inSql | 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 | 字段 NOT IN ( sql语句 ) | notInSql(“id”, “select id from table where id < 3”) | age not in (select id from table where id < 3) |
| groupBy | 分组：GROUP BY 字段1, … | groupBy(“id”, “name”) | group by id, name |
| orderByAsc | 升序排序：ORDER BY 字段1, … ASC | orderByAsc(“id”, “name”) | order by id ASC, name ASC |
| orderByDesc | 降序排序：ORDER BY 字段1, … DESC | orderByDesc(“id”, “name”) | order by id DESC, name DESc |
| orderBy | 排序：ORDER BY 字段1, … | orderBy(true, true, “id”，“name”) | orderBy(true,，true,“id”，“name”) |
| having | HAVING ( sql 语句 ) | having(“sum(age) > {0}”，11) | having sum(age) > 11 |
| or | 拼接 OR | 主动调用or表示紧接着下一个方法不是用and连接!(不调用or则默认为使用and连接) | |
| and | 拼接 ADN | 默认连接符 | |
| apply | 拼接 sql | 例: apply(“date_format(dateColumn, ‘%Y-%m-%d’) = {0}”，“2008-08-08”)—>date_format(dateColumn,‘%Y-%m-%d’) = ’2008-08-08’") 该方法可用于数据库函数动态入参的params对应前面sqlHaving内部的{index}部分.这样是不会有sql注入风险的，反之会有! | |
| last | 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。 | 例如 last(“limit 1”) | (limit 1) |
| exists | 拼接 EXISTS | exists(“select id from table where age = 18”) | exists(select id from table where age = 18) |
| notExists | 拼接 NOT EXISTS | notExists(“select id from table where age = 18”) | not exists(“select id from table where age = 18”) |
| nested | 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’) |
List<SysDept> deptAllList = deptMapper.selectList(
Wrappers.<SysDept>lambdaQuery().like(StrUtil.isNotBlank(deptName), SysDept::getName, deptName));