MongoDB：如何获取不同的子文档字段值列表？ [英] MongoDB: How to get distinct list of sub-document field values?

问题描述

假设我收集了以下文件：

Let's say I have the following documents in collection:

{
   "family": "Smith",
   "children": [
        {
            "child_name": "John"
        },
        {
            "child_name": "Anna"
        },
    ]
}

{
   "family": "Williams",
   "children": [
        {
            "child_name": "Anna"
        },
        {
            "child_name": "Kevin"
        },
    ]
}

现在我想以某种方式获得以下所有家庭中唯一的孩子名字列表：

Now I want to get somehow the following list of unique child names cross all families:

[ "John", "Anna", "Kevin" ]

结果的结构可能不同。如何在MongoDB中实现？应该很简单，但我不知道。我在集合上尝试了aggregate（）函数，但是后来我不知道如何应用distinct（）函数。

Structure of result might be different. How to achieve that in MongoDB? Should be something simple but I can't figure out. I tried aggregate() function on collection but then I don't know how to apply distinct() function.

推荐答案

只需这样做：

db.collection.distinct("children.child_name");

在您的情况下，它返回：

In your case it returns:

[ "John", "Anna", "Kevin" ]

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