Apache Camel：如何将层次数据从数据库转换为pojo

Question

2.Select query返回具有正确结构的JSON以转换为pojo

select json_object(
      'parentProperty1', parentProperty1
    , 'parentProperty2', parentProperty2
    , 'children', (select CAST(CONCAT('[',
                GROUP_CONCAT(
                  JSON_OBJECT(  
                          'childProperty1', childProperty1
                        , 'childProperty2', childProperty2
                        )),
                ']')
         AS JSON) 
        from childTable c
        where p.messageId=c.messageId
        )
    ))  
from parentTable p
;

在mysql shell上执行查询将返回预期的JSON：

{
    "parentProperty1": "value1",
    "parentProperty1": "value2",
    "children": [
        {
            "childProperty1": "value3",
            "childProperty2": "value4"
        },
        {
            "childProperty1": "value5",
            "childProperty2": "value6"
        }
    ]
}

在camel中运行查询时，我遇到了一个问题，对此我无法找到解释或解决方案。

[{json_object('parentProperty1', parentProperty1 , 'parentProperty2', parentProperty2 , 'children', (select CAST(CONCAT('[',
={"parentProperty1": "value1", "parentProperty2": "value2", "children": [{"childProperty1": "value3", "childProperty2": "value4"}, {"childProperty1": "value5", "childProperty2": "value6"}]}}]

null

提前致谢

Answer 1

您实际上得到的是一个键值对。由于查询中没有为json_obect提供别名，所以mysql生成默认列名。这就是您在结果中看到的查询片段。

向查询中的json_obect添加别名，如下所示：

    select json_object(
      'parentProperty1', parentProperty1
    , 'parentProperty2', parentProperty2
    , 'children', (select CAST(CONCAT('[',
                GROUP_CONCAT(
                  JSON_OBJECT(  
                          'childProperty1', childProperty1
                        , 'childProperty2', childProperty2
                        )),
                ']')
         AS JSON) 
        from childTable c
        where p.messageId=c.messageId
        )
    ) as result  
from parentTable p;

这将返回如下内容：

{result={"children": [{"childProperty1": "value3", "childProperty2": "value4"}, {"childProperty1": "value5", "childProperty2": "value6"}], "parentProperty1": "value1", "parentProperty2": "value2"}}