We have documents that were originally stored using the StringObjectIdGenerator type for _id. Newer data will be saved using the default ObjectIdGenerator. We would like to be able to migrate the existing data by converting the _id to the new data type. Is this possible?
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3 Answers
Yes, it's possible to change data type, we need to find all documents with string id, using the iterator we can clone a document by changing its _id, after cloning we just need to delete the old document.
Below is for a small document, for large collection you may need to use db.collection.initializeUnorderedBulkOp() for bulk insert/delete
db.i.find({_id : {$type : 2}}). //find all string _id
forEach(function(d){
var id = ObjectId(d._id); //_id to ObjectId
var oldId = d._id; // _id
d._id = id;
db.i.insert(d); // clone doc with new Id
db.i.remove({ _id : oldId }); // delete old doc
}
)
Example
> db.i.insertMany([{},{},{},{_id : "4a5ec389fee4c182f509f3ba"}, {_id : "4b5ec389fee4c182f509f3ba"}])
{
"acknowledged" : true,
"insertedIds" : [
ObjectId("5a5ec9edfee4c182f509f3c9"),
ObjectId("5a5ec9edfee4c182f509f3ca"),
ObjectId("5a5ec9edfee4c182f509f3cb"),
"4a5ec389fee4c182f509f3ba",
"4b5ec389fee4c182f509f3ba"
]
}
> db.i.find()
{ "_id" : ObjectId("5a5ec9edfee4c182f509f3c9") }
{ "_id" : ObjectId("5a5ec9edfee4c182f509f3ca") }
{ "_id" : ObjectId("5a5ec9edfee4c182f509f3cb") }
{ "_id" : "4a5ec389fee4c182f509f3ba" }
{ "_id" : "4b5ec389fee4c182f509f3ba" }
> db.i.find({_id : {$type : 2}}).
... forEach(function(d){
... var id = ObjectId(d._id);
... var oldId = d._id;
... d._id = id;
... db.i.insert(d);
... db.i.remove({ _id : oldId });
... }
... )
> db.i.find()
{ "_id" : ObjectId("5a5ec9edfee4c182f509f3c9") }
{ "_id" : ObjectId("5a5ec9edfee4c182f509f3ca") }
{ "_id" : ObjectId("5a5ec9edfee4c182f509f3cb") }
{ "_id" : ObjectId("4a5ec389fee4c182f509f3ba") }
{ "_id" : ObjectId("4b5ec389fee4c182f509f3ba") }
>
1 Comment
Udit Bhardwaj
the remove statement should be above the insert statement, as inserting before removing existing document on indexed collection can result in duplicate index error i.e. unique index.
db.inventries.find({ _id: { $type: 2 } }).forEach(function (d) { var id = ObjectId(d._id); var oldId = d._id; d._id = id; db.inventries.insert(d); db.inventries.remove({ _id: oldId }); } )
// change inventries => your collection name
hit above commend in mongodb console
Comments
db.getCollection('Files').find({"_id":{"$exists":true}}).forEach(function(x){
let id;
try {
id = new ObjectId(x._id);
}
catch (err) {
id = new ObjectId();
}
db.Files.update( { "_id": x._id}, { $set: { _id:id } } );
}
)
