How update the _id of one MongoDB Document?

问题:

I want update an _id MongoDB of one document. I know it\'s not a really good pratice. But with some technical reason, I need update it. But If I try to update it I have :

> db.clients.update({\'_id\':ObjectId(\"4cc45467c55f4d2d2a000002\")}, {\'$set\':{\'_id\':ObjectId(\"4c8a331bda76c559ef000004\")}});
Mod on _id not allowed

And the update is not made. How I can really update it ?

回答1:

You cannot update it. You\'ll have to save the document using a new _id, and then remove the old document.

// store the document in a variable
doc = db.clients.findOne({_id: ObjectId(\"4cc45467c55f4d2d2a000002\")})

// set a new _id on the document
doc._id = ObjectId(\"4c8a331bda76c559ef000004\")

// insert the document, using the new _id
db.clients.insert(doc)

// remove the document with the old _id
db.clients.remove({_id: ObjectId(\"4cc45467c55f4d2d2a000002\")})

回答2:

To do it for your whole collection you can also use a loop (based on Niels example):

db.status.find().forEach(function(doc){ 
    doc._id=doc.UserId; db.status_new.insert(doc);
});
db.status_new.renameCollection(\"status\", true);

In this case UserId was the new ID I wanted to use

回答3:

In case, you want to rename _id in same collection (for instance, if you want to prefix some _ids):

db.someCollection.find().snapshot().forEach(function(doc) { 
   if (doc._id.indexOf(\"2019:\") != 0) {
       print(\"Processing: \" + doc._id);
       var oldDocId = doc._id;
       doc._id = \"2019:\" + doc._id; 
       db.someCollection.insert(doc);
       db.someCollection.remove({_id: oldDocId});
   }
});

if (doc._id.indexOf(\"2019:\") != 0) {... needed to prevent infinite loop, since forEach picks the inserted docs, even throught .snapshot() method used.

回答4:

Here I have a solution that avoid multiple requests, for loops and old document removal.

You can easily create a new idea manually using something like:_id:ObjectId() But knowing Mongo will automatically assign an _id if missing, you can use aggregate to create a $project containing all the fields of your document, but omit the field _id. You can then save it with $out

So if your document is:

{
\"_id\":ObjectId(\"5b5ed345cfbce6787588e480\"),
\"title\": \"foo\",
\"description\": \"bar\"
}

Then your query will be:

    db.getCollection(\'myCollection\').aggregate([
        {$match:
             {_id: ObjectId(\"5b5ed345cfbce6787588e480\")}
        }        
        {$project:
            {
             title: \'$title\',
             description: \'$description\'             
            }     
        },
        {$out: \'myCollection\'}
    ])