如何使用MQL编写条件查询?

I try to extract some extra information if my query returns a result.

如果我的查询返回一个结果，我尝试提取一些额外的信息。

For example in this query, notable_for returns as "/music/musical_group" and I want to merge another query to extract some information about "/music/musical_group" like its "name"

例如，在这个查询中，notable_for返回为“/music/musical_group”，我想合并另一个查询来提取关于“/music/musical_group”的一些信息，比如它的“名称”

[{
 "id": "/en/pearl_jam",
"mid":None,
"/common/topic/notable_for": [],
"name":[]   
}]

But if it does not return anything I dont want my query fails. For example, for the query below it returns a null list for the field "notable_for"

但是如果它不返回任何东西，我就不希望我的查询失败。例如，对于下面的查询，它为字段“notable_for”返回一个空列表

[{
"id": "/music/musical_group",
"mid":None,
"/common/topic/notable_for": [],
"name":[]
}]

How should I envelope my queries for such purpose?

我该如何将我的查询封装起来?

2 个解决方案

#1

You chose a pseudoproperty (*/common/topic/notable_for*) rather than a real property as your example and it behaves a little bit differently. For a real property, you can use @masouras's shorthand notation ([{}]) if you want to get all subproperties, but if you wanted to pick, say, one or two, the trick is to use the "optional" keyword.

您选择了一个pseudoproperty (*/common/topic/notable_for*)，而不是一个实际的属性作为示例，它的行为稍有不同。对于一个真正的属性，如果想要获得所有子属性，可以使用@masouras的简化符号([{}])，但是如果您想要选择，比方说，一两个，诀窍是使用“可选”关键字。

For example, this query:

例如,这个查询:

[{
  "id":  "/m/01mntvx",
  "type":"/music/musical_group",
  "/music/musical_group/member": [{
    "member": {
      "name": null
    },
    "optional": true
  }],
  "name":null
}]

will work even if a the band had no members listed.

即使乐队没有成员名单也能工作。

#2

Is this what you are asking:

这就是你要问的:

[{ "id": "/en/pearl_jam", "mid": null, "/common/topic/notable_for": [{}], }]

[{ " id ":" / en / pearl_jam”、“中期”:null," /共同/主题/ notable_for”:({ })})

http://tinyurl.com/7tchree

#1