mongodb 在更新中设置为空 [英] mongodb set null in update

问题描述

我必须交换文档的值.

var query = {"_id" : ObjectId("53e1c254382f891cc600076d")};

db.properties.find(query).forEach(function(prop){
   printjson({"_id":prop._id, "val":prop.val, "ua":prop.ua});
   db.properties.update(query, {$set:{ua: prop.val}},{$unset:{val:""}});
});

更新操作前，文档如下所示:

Before update operation, document looks like this:

{
    "_id" : ObjectId("53e1c254382f891cc600076d"),
    "val" : 9876541,
    "ua" : null
}

更新后变成:

{
    "_id" : ObjectId("53e1c254382f891cc600076d"),
    "val" : 9876541,
    "ua" : 9876541
}

但我希望它是:

{
    "_id" : ObjectId("53e1c254382f891cc600076d"),
    "val" : null,
    "ua" : 9876541
}

但它不起作用.还设置 "val" null ({$set:{val:null}}) 直接删除了我的整个文档.

But its not working. also setting "val" null ({$set:{val:null}}) directly it deleted my entire document.

推荐答案

Setting undefined，效果很赞！！

Setting undefined, It worked like a charm!!

db.properties.find(query).forEach(function(prop){
    db.properties.update(query, {$set:{ua: prop.val, val:undefined}}); 
});

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