MongoDB:获取所有唯一标签列表的好方法是什么? [英] MongoDB: What's a good way to get a list of all unique tags?

问题描述

跟踪成千上万个大型项目的文档集合的唯一标签的最佳方法是什么?进行标记的通常方法似乎是索引多键.不过，我经常需要获取所有唯一键.我也无法访问mongodb的新"distinct"命令，因为我的驱动程序erlmongo似乎尚未实现.

What's the best way to keep track of unique tags for a collection of documents millions of items large? The normal way of doing tagging seems to be indexing multikeys. I will frequently need to get all the unique keys, though. I don't have access to mongodb's new "distinct" command, either, since my driver, erlmongo, doesn't seem to implement it, yet.

推荐答案

即使您的驱动程序没有实现distinct，也可以自己实现.用JavaScript(对不起，我不知道Erlang，但是它应该直接翻译)可以说:

Even if your driver doesn't implement distinct, you can implement it yourself. In JavaScript (sorry, I don't know Erlang, but it should translate pretty directly) can say:

result = db.$cmd.findOne({"distinct" : "collection_name", "key" : "tags"})

也就是说，您在使用任何数据库的"$ cmd"集合上执行一个findOne.向其传递集合名称和您要在其上运行的键.

So, that is: you do a findOne on the "$cmd" collection of whatever database you're using. Pass it the collection name and the key you want to run distinct on.

如果您需要驱动程序不提供帮助的命令，可以查看 http://www.mongodb.org/display/DOCS/List+of+Database+Commands 以获得完整的数据库命令列表.

If you ever need a command your driver doesn't provide a helper for, you can look at http://www.mongodb.org/display/DOCS/List+of+Database+Commands for a somewhat complete list of database commands.

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