MongoDB聚合框架 - 按年分组 [英] MongoDB Aggregate Framework - Group by Year

问题描述

我一直在尝试使用聚合函数按年份对日期字段进行分组：

I've been trying to use the aggregate function to group date fields by year:

db.identities.aggregate([
{
    $group : {
        _id : { year : {$year : "$birth_date"}},
        total : {$sum : 1}
        }
    }   
])

然而我的一些日期在1970年之前下降作为Windows用户，我得到一个关于gmtime的令人讨厌的错误：

Some of my dates however fall before 1970 and being a Windows user I get a nasty error about gmtime:

{
    "errmsg" : "exception: gmtime failed - your system doesn't support dates before 1970",
    "code" : 16422,
    "ok" : 0
}

我知道现在显而易见的答案是让我运行虚拟机或其他东西，但我很好奇是否有任何针对Windows的解决方案（Windows 7 in我的情况）。如果没有多少性能影响将日期存储为嵌套对象，那就是：

I know the obvious answer now is for me to get a virtual machine running or something but I was just curious if there were any work-arounds for windows (Windows 7 in my case). Failing that how much of a performance hit would storing the date as a nested object be i.e:

birth_date : {
  year : 1980,
  month : 12,
  day : 9
}

我不太确定索引等会有多忙。

I'm not too sure how hectic that would be with indexes etc.

任何建议都值得赞赏！

推荐答案

已知某些版本的Windows可以正常工作。你有没有机会使用32位操作系统？有问题的代码是这里，取决于 gmtime_s（）实现。

Some versions of Windows have been known to work. By any chance, are you using a 32-bit OS? The code in question is here, and depends upon the gmtime_s() implementation.

如果此集合仅用于聚合查询，则可以将日期组件存储在对象中。我建议缩写字段名称（例如 y ， m ， d ）保存存储，因为字段字符串存在于每个存储的文档中。这里的权衡是不能使用任何聚合日期运算符。您可能希望将时间戳存储为有符号整数（例如 ts ），以便在必要时可以轻松地进行范围查询。

If this collection is simply for aggregation queries, you can certainly get by with storing date components in an object. I'd suggest abbreviating the field names (e.g. y, m, d) to save on storage, since the field strings are present in each stored document. The trade-off here is that none of the aggregation date operators can be used. You may want to store the timestamp as a signed integer (e.g. ts) so that you can easily do range queries if necessary.

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