mybatis 返回LIst<List<String>>

MyBatis可以返回List<List<String>>，这样的数据结构。可以使用嵌套查询或者使用结果集映射来实现。下面是一些示例代码：

1. 使用嵌套查询：

@Select("SELECT * FROM table")
@Results({
    @Result(column = "id", property = "id"),
    @Result(column = "name", property = "name"),
    @Result(column = "details", property = "details", javaType = List.class, many = @Many(select = "getDetails"))
})
List<Map<String, Object>> getData();

@Select("SELECT details FROM table_details WHERE id = #{id}")
List<String> getDetails(int id);

2. 使用结果集映射：

@Select("SELECT * FROM table")
@Results({
    @Result(column = "id", property = "id"),
    @Result(column = "name", property = "name"),
    @Result(column = "details", property = "details", javaType = List.class, typeHandler = ListTypeHandler.class)
})
List<Data> getData();

public class Data {
    private int id;
    private String name;
    private List<List<String>> details;

    // getters and setters
}

@MappedTypes(List.class)
@MappedJdbcTypes(JdbcType.VARCHAR)
public class ListTypeHandler extends BaseTypeHandler<List<String>> {
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, List<String> parameter, JdbcType jdbcType) throws SQLException {
        // 将List转换为字符串，存储到数据库中
        String detailsString = String.join(",", parameter);
        ps.setString(i, detailsString);
    }

    @Override
    public List<String> getNullableResult(ResultSet rs, String columnName) throws SQLException {
        // 从数据库中读取字符串，转换为List
        String detailsString = rs.getString(columnName);
        return Arrays.asList(detailsString.split(","));
    }

    // 其他方法省略...
}

这些代码示例中，使用了@Select注解来定义查询语句，@Results注解用于配置结果集映射。对于嵌套查询，可以使用@Many注解指定要执行的子查询语句。对于结果集映射，可以使用自定义的TypeHandler来处理List<List<String>>类型的数据。