带投影的查找查询中的排序字段 [英] Ordering fields from find query with projection

问题描述

我有一个Mongo查找查询，可以很好地从大型文档中提取特定字段，例如...

I have a Mongo find query that works well to extract specific fields from a large document like...

db.profiles.find(
  { "profile.ModelID" : 'LZ241M4' },
  {
    _id : 0,
    "profile.ModelID" : 1,
    "profile.AVersion" : 2,
    "profile.SVersion" : 3
  }
);

...这将产生以下输出.请注意，即使我的投影要求在SVersion之前要求AVersion，SVersion还是比文档中的AVersion早.

...this produces the following output. Note how the SVersion comes before the AVersion in the document even though my projection asked for AVersion before SVersion.

{ "profile" : { "ModelID" : "LZ241M4", "SVersion" : "3.5", "AVersion" : "4.0.3" } }
{ "profile" : { "ModelID" : "LZ241M4", "SVersion" : "4.0", "AVersion" : "4.0.3" } }

...问题是我希望输出是...

...the problem is that I want the output to be...

{ "profile" : { "ModelID" : "LZ241M4", "AVersion" : "4.0.3", "SVersion" : "3.5" } }
{ "profile" : { "ModelID" : "LZ241M4", "AVersion" : "4.0.3", "SVersion" : "4.0" } }

我该怎么做才能使Mongo JavaScript Shell以我指定的字段顺序显示查询结果?

What do I have to do get the Mongo JavaScript shell to present the results of my query in the field order that I specify?

推荐答案

我现在明白了.您想返回按字段"排序的结果，而不是字段的值.

I get it now. You want to return results ordered by "fields" rather the value of a fields.

简单的答案是您不能这样做.新的聚合框架也许有可能.但这似乎只是为了订购字段就显得过分了.

Simple answer is that you can't do this. Maybe its possible with the new aggregation framework. But this seems overkill just to order fields.

查找查询中的第二个对象用于包括或排除不用于排序的返回字段.

The second object in a find query is for including or excluding returned fields not for ordering them.

  {
    _id : 0,               // 0 means exclude this field from results
    "profile.ModelID" : 1, // 1 means include this field in the results
    "profile.AVersion" :2, // 2 means nothing
    "profile.SVersion" :3, // 3 means nothing
  }

最后一点，您不需要这样做，谁在乎字段以什么顺序返回. 您的应用程序应该能够利用其所需的字段，而不考虑字段的顺序.

Last point, you shouldn't need to do this, who cares what order the fields come-back in. You application should be able to make use of the fields it needs regardless of the order the fields are in.

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