如何将 Mongo DB 聚合结果附加到现有集合? [英] How do I append Mongo DB aggregation results to an existing collection?

问题描述

我正在尝试使用以下代码对现有的 Mongo DB 集合执行多次插入

db.dados_meteo.aggregate([{ $match : { "POM" : "AguiardaBeira" } },{ $项目:{_id : { $concat: ["0001:",{ $substr: [ "$DTM", 0, 4 ] },{ $substr: [ "$DTM", 5, 2 ] },{ $substr: [ "$DTM", 8, 2 ] },{ $substr: [ "$DTM", 11, 2 ] },{ $substr: [ "$DTM", 14, 2 ] },{ $substr: [ "$DTM", 17, 2 ] }] },RNF":1，湿":1，HMD":1，TMP":1 } }，{ $out : "dados_meteo_reloaded" }])

但是每次我更改 $match 参数并进行新的聚合时，Mongo DB 都会删除以前的文档并插入新的结果.

你能帮帮我吗?

解决方案

简短的回答是你不能":

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如果 $out 操作指定的集合已经存在，那么在聚合完成后，$out 阶段会自动将现有集合替换为新的结果集合.$out 操作不会更改先前集合中存在的任何索引.如果聚合失败，$out 操作不会更改预先存在的集合.

作为一种解决方法，您可以在聚合之后将由 $out 指定的集合文档复制到永久"集合中，方法有以下几种(但其中一种都不是理想的):

• copyTo() 是最简单的，请注意警告.不要为了小的结果而使用其他.
• 使用JS:db.out.find().forEach(function(doc) {db.target.insert(doc)})
• 使用 mongoexport/mongoimport

I am trying to perform several insertions on an existent Mongo DB collection using the following code

db.dados_meteo.aggregate( [
                  { $match : { "POM" : "AguiardaBeira" } },
                  { $project : {
                     _id : { $concat: [
                        "0001:",
                      { $substr: [ "$DTM", 0, 4 ] },
                      { $substr: [ "$DTM", 5, 2 ] },
                      { $substr: [ "$DTM", 8, 2 ] },
                      { $substr: [ "$DTM", 11, 2 ] },
                      { $substr: [ "$DTM", 14, 2 ] },
                      { $substr: [ "$DTM", 17, 2 ] }
                       ] },
                    "RNF" : 1, "WET":1,"HMD":1,"TMP":1 } },
                  { $out : "dados_meteo_reloaded" }
              ] )

But each time I change the $match parameters and make a new aggregation, Mongo DB deletes the previous documents and inserts the new result.

Could you help me?

解决方案

The short answer is "you can't":

If the collection specified by the $out operation already exists, then upon completion of the aggregation, the $out stage atomically replaces the existing collection with the new results collection. The $out operation does not change any indexes that existed on the previous collection. If the aggregation fails, the $out operation makes no changes to the pre-existing collection.

As a workaround, you can copy the collection document specified by $out to a "permanent" collection just after aggregation, in one of a several ways (non of which is ideal though):

• copyTo() is the easiest, mind the Warning. Don't use other for small results.
• Use JS: db.out.find().forEach(function(doc) {db.target.insert(doc)})
• Use mongoexport / mongoimport

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