在MongoDB中返回ID周围的文档范围 [英] Return range of documents around ID in MongoDB

问题描述

我有一个文档的ID，需要返回该文档以及之前的10个文档和之后的10个文档.共21篇文档.

I have an ID of a document and need to return the document plus the 10 documents that come before and the 10 documents after it. 21 docs total.

我没有任何键的开始或结束值.仅在任一方向都有限制.

I do not have a start or end value from any key. Only the limit in either direction.

做到这一点的最佳方法?预先谢谢你.

Best way to do this? Thank you in advance.

推荐答案

您知道吗 ObjectID的是否包含时间戳?因此，它们始终代表自然的插入顺序.因此，如果要在已知文档_id之后查找文档，可以执行以下操作:

Did you know that ObjectID's contain a timestamp? And that therefore they always represent the natural insertion order. So if you are looking for documents before an after a known document _id you can do this:

我们的文件

{ "_id" : ObjectId("5307f2d80f936e03d1a1d1c8"), "a" : 1 }
{ "_id" : ObjectId("5307f2db0f936e03d1a1d1c9"), "b" : 1 }
{ "_id" : ObjectId("5307f2de0f936e03d1a1d1ca"), "c" : 1 }
{ "_id" : ObjectId("5307f2e20f936e03d1a1d1cb"), "d" : 1 }
{ "_id" : ObjectId("5307f2e50f936e03d1a1d1cc"), "e" : 1 }
{ "_id" : ObjectId("5307f2e90f936e03d1a1d1cd"), "f" : 1 }
{ "_id" : ObjectId("5307f2ec0f936e03d1a1d1ce"), "g" : 1 }
{ "_id" : ObjectId("5307f2ee0f936e03d1a1d1cf"), "h" : 1 }
{ "_id" : ObjectId("5307f2f10f936e03d1a1d1d0"), "i" : 1 }
{ "_id" : ObjectId("5307f2f50f936e03d1a1d1d1"), "j" : 1 }
{ "_id" : ObjectId("5307f3020f936e03d1a1d1d2"), "j" : 1 }

所以我们知道"f"的_id，获取它以及接下来的2个文档:

So we know the _id of "f", get it and the next 2 documents:

> db.items.find({ _id: {$gte: ObjectId("5307f2e90f936e03d1a1d1cd") } }).limit(3)

{ "_id" : ObjectId("5307f2e90f936e03d1a1d1cd"), "f" : 1 }
{ "_id" : ObjectId("5307f2ec0f936e03d1a1d1ce"), "g" : 1 }
{ "_id" : ObjectId("5307f2ee0f936e03d1a1d1cf"), "h" : 1 }

并相反地做同样的事情:

And do the same in reverse:

> db.items.find({ _id: {$lte: ObjectId("5307f2e90f936e03d1a1d1cd") } })
    .sort({ _id: -1 }).limit(3)
{ "_id" : ObjectId("5307f2e90f936e03d1a1d1cd"), "f" : 1 }
{ "_id" : ObjectId("5307f2e50f936e03d1a1d1cc"), "e" : 1 }
{ "_id" : ObjectId("5307f2e20f936e03d1a1d1cb"), "d" : 1 }

与扫描集合相比，这是一种更好的方法.

And that's a much better approach than scanning a collection.

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