Syntax error Get number of updated documents in MongoDB?

Get number of updated documents in MongoDB?

To get number of updated documents in MongoDB, you need to use runCommand along with getlasterror.

Let us first create a collection with documents

> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"David"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5ca28c1d6304881c5ce84bad")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Chris"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5ca28c226304881c5ce84bae")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Robert"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5ca28c276304881c5ce84baf")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Ramit"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5ca28c366304881c5ce84bb0")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Adam"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5ca28c436304881c5ce84bb1")
}

Following is the query to display all documents from a collection with the help of find() method:

> db.getNumberOfUpdatedDocumentsDemo.find().pretty();

This will produce the following output

{ "_id" : ObjectId("5ca28c1d6304881c5ce84bad"), "StudentName" : "David" }
{ "_id" : ObjectId("5ca28c226304881c5ce84bae"), "StudentName" : "Chris" }
{ "_id" : ObjectId("5ca28c276304881c5ce84baf"), "StudentName" : "Robert" }
{ "_id" : ObjectId("5ca28c366304881c5ce84bb0"), "StudentName" : "Ramit" }
{ "_id" : ObjectId("5ca28c436304881c5ce84bb1"), "StudentName" : "Adam" }

Following is the query to update documents

> db.getNumberOfUpdatedDocumentsDemo.update({}, {$set : {"StudentName" : "Carol"}}, true, true);
WriteResult({ "nMatched" : 5, "nUpserted" : 0, "nModified" : 5 })
Now, get the number of updated documents:
> db.runCommand( "getlasterror" );

Following is the output displaying n =5 i.e. 5 documents have been updated

{
   "connectionId" : 4,
   "updatedExisting" : true,
   "n" : 5,
   "syncMillis" : 0,
   "writtenTo" : null,
   "err" : null,
   "ok" : 1
}

Now display all documents from a collection

> db.getNumberOfUpdatedDocumentsDemo.find().pretty();

This will produce the following output

{ "_id" : ObjectId("5ca28c1d6304881c5ce84bad"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c226304881c5ce84bae"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c276304881c5ce84baf"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c366304881c5ce84bb0"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c436304881c5ce84bb1"), "StudentName" : "Carol" }
Updated on: 2019-07-30T22:30:25+05:30

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