在mongodb上合并两个集合 [英] Merge two collections on mongodb

问题描述

我需要将两个集合合并为一个，但是仅当第一个集合中不存在该文档时，才需要放置该文档.我该怎么做?最好的方法是什么? 我看到了一些有关聚合和mapreduce的信息，但是我不确定该使用什么.你能帮我吗?

I need to merge two collections into one, but I need to put the document only if it doesn't exists in the first collection. How can I do it? What's the best way? I saw something about agregation and mapreduce but I am not sure about what to use. Can you help me, please?

推荐答案

我认为没有自动的方法. 假设您有2个要合并的集合，即c1和c2 您可以手动进行合并

I think there is no automatic way for that. Assume u have 2 collection for merge, c1 and c2 You could manually do the merge with

db.c1.find().forEach(function(item) {
    db.c2.insert(item);
    db.c1.remove(item);
});

您应该注意这一点，因为mongo不支持多文档交易

u should be careful with that because mongo does not support multi-document-transaction

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