Mongodb-$ set和$ setOnInsert中的重复字段 [英] Mongodb - duplicate fields in $set and $setOnInsert

问题描述

在 帖子，接受的答案说明您在upsert操作中的$set和$setOnInsert下不能有相同的字段.

In this post, the accepted answer explains that you cannot have the same fields under $set and $setOnInsert in an upsert operation.

有人可以解释为什么会这样吗?似乎$setOnInsert不应与$set冲突，因为前者在插入文档时使用，而后者在更新文档时使用.

Can someone explain why this is? It seems like the $setOnInsert shouldn't conflict with $set, since the former is used when a document is inserted, and the latter is used when the document is updated.

推荐答案

$ set 运算符也用于 upsert .因此，在 $ set 和 $ setOnInsert 上引用相同的字段是没有意义的.

$set operator is used on upsert too. So it's nonsense to refer same fields both on $set and $setOnInsert.

只需在一个空集合上尝试一下:

Just try this on an empty collection:

db.items.remove();
db.items.update({},{$set:{a:1},$setOnInsert:{b:2}},{upsert:1})
db.items.find({});

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