NodeJS + Mongo：如果不存在则插入，否则 - 更新
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NodeJS + Mongo: Insert if not exists, otherwise - update
提问by f1nn
I have an object in my mongodb collection. Its schema is:
我的 mongodb 集合中有一个对象。它的架构是：
{
"instruments": ["A", "B", "C"],
"_id": {
"$oid": "508510cd6461cc5f61000001"
}
}
My collection may have such object, but may not. I need to check if object with key "instruments" exists (please, notе, I don't know what value "instrument" is at this time, it may contain any value or an array), and if exists - perform update, otherwise – insert a new value. How can I do this?
我的收藏可能有这样的对象，但可能没有。我需要检查带有键“instruments”的对象是否存在（请注意，此时我不知道“instrument”是什么值，它可能包含任何值或数组），如果存在 - 执行更新，否则– 插入一个新值。我怎样才能做到这一点？
collection.find( { "instruments" : { $exists : true } }, function(err, object){
if (object) {
//update
} else {
//insert
}
});
doesn't work ((
不起作用（（
回答by Gianfranco P.
If you want to insert one document if it is not found, you can use the upsertoption in the update()method:
如果想插入一个找不到的文档，可以使用方法中的upsert选项update()：
collection.update(_query_, _update_, { upsert: true });
See docs for the upsertbehavior.
有关upsert行为，请参阅文档。
An example with the $existsoperator.
$exists运营商的例子。
Let's say you have 6 documents in your collection:
假设您的集合中有 6 个文档：
> db.test.find()
{ "_id": ObjectId("5495aebff83774152e9ea6b2"), "a": 1 }
{ "_id": ObjectId("5495aec2f83774152e9ea6b3"), "a": [ ] }
{ "_id": ObjectId("5495aec7f83774152e9ea6b4"), "a": [ "b" ] }
{ "_id": ObjectId("5495aecdf83774152e9ea6b5"), "a": [ null ] }
{ "_id": ObjectId("5495aed5f83774152e9ea6b7"), "a": [ 0 ] }
{ "_id": ObjectId("5495af60f83774152e9ea6b9"), "b": 2 }
and you want to find documents that have a certain field "a"), you can use find()method with the $existsoperator (node docs). Note: this will also return documents which field is an empty array.
并且您想查找具有特定字段的文档"a"），您可以使用find()带有$exists运算符的方法（节点文档）。注意：这也将返回字段为空数组的文档。
> db.test.find( { a: { $exists: true } } )
{ "_id": ObjectId("5495aebff83774152e9ea6b2"), "a": 1 }
{ "_id": ObjectId("5495aec2f83774152e9ea6b3"), "a": [ ] }
{ "_id": ObjectId("5495aec7f83774152e9ea6b4"), "a": [ "b" ] }
{ "_id": ObjectId("5495aecdf83774152e9ea6b5"), "a": [ null ] }
{ "_id": ObjectId("5495aed5f83774152e9ea6b7"), "a": [ 0 ] }
