How to update collection value - node.js

Question

Assume I have db as;
{ name: "alex" , id: "1"}
I want to update the collection. I want to add "Mr." to the value in name field.
{ name: "Mr.alex" , id: "1"}
How can I do this? Should I wrote 2 query as;
db.collection("user").find({id : "1"}).toArray(function(err, result){
var name = result[0].name;
db.collection("user").updateOne({id : "1"}, {name: "Mr." + name},function(err, result){
})
})
Isn't there any better way to do this as x = x+1 in mongodb?

Answer 1

AFAIK there would be two queries, update operator won't take any field's value and need provided value.
However if you need to do it for all the document or large amount of document, you can write a script and use cursor forEach and for each document change the name and call db.user.save() by passing the argument user object.
Bottom line remains same.

Answer 2

try below:
var cursor = db.users.find({});
while (cursor.hasNext()) {
var user = cursor.next();
user.name = "Mr." + user.name;
user.save();
}
Not possible using one query. You have to iterate through the documents and save them with updated result.

Answer 3

Currently there is no way to reference the retrieved document in the same query, which would allow you to find and update a document within the same operation.
Thus, you will have to make multiple queries to accomplish what you are looking for:
/*
* Single Document
*/
// I'm assuming the id field is unique and can only return one document
var doc = db.collection('user').findOne({ id: '1' });
try {
db.collection('user').updateOne({ id: '1' }, { $set: { name: 'Mr. ' + doc.name }});
} catch (e) {
print(e);
}
If you want to handle multiple update operations, you can do so by using a Bulk() operations builder:
/*
* Multiple Documents
*/
var bulk = db.collection('user').initializeUnorderedBulkOp();
// .forEach is synchronous in MongoDB, as it performs I/O operations
var users = db.collection('user').find({ id: { $gt: 1 } }).forEach(function(user) {
bulk.find({ id: user.id }).update({ $set: { name: 'Mr. ' + user.name }});
});
bulk.execute();

Answer 4

The key to updating the collection with the existing field is to loop through the array returned from the find().toarray() cursor method and update your collection using the Bulk API which allows you to send many update operations within a single request (as a batch).
Let's see with some examples how this pens out:
a) For MongoDB server version 3.2 and above
db.collection("user").find({id : "1"}).toArray(function(err, result){
var operations = [];
result.forEach(function(doc){
operations.push({
"updateOne": {
"filter": {
"_id": doc._id,
"name": doc.name
},
"update": {
"$set": { "name": "Mr." + doc.name }
}
}
});
// Send once in 500 requests only
if (operations.length % 500 === 0 ) {
db.collection("user").bulkWrite(operations, function(err, r) {
// do something with result
}
operations = [];
}
});
// Clear remaining queue
if (operations.length > 0) {
db.collection("user").bulkWrite(operations, function(err, r) {
// do something with result
}
}
})
In the above, you initialise your operations array which would be used by the Bulk API's bulkWrite() function and holds the update operations.
The result from the find().toarray() cursor function is then iterated to create the operations array with the update objects. The operations are limited to batches of 500.
The reason of choosing a lower value than the default batch limit of 1000 is generally a controlled choice. As noted in the documentation there, MongoDB by default will send to the server in batches of 1000 operations at a time at maximum and there is no guarantee that makes sure that these default 1000 operations requests actually fit under the 16MB BSON limit.
So you would still need to be on the "safe" side and impose a lower batch size that you can only effectively manage so that it totals less than the data limit in size when sending to the server.
a) If using MongoDB v3.0 or below:
// Get the collection
var col = db.collection('user');
// Initialize the unordered Batch
var batch = col.initializeUnorderedBulkOp();
// Initialize counter
var counter = 0;
col.find({id : "1"}).toArray(function(err, result){
result.forEach(function(doc) {
batch.find({
"_id": doc._id,
"name": doc.name
}).updateOne({
"$set": { "name": "Mr. " + doc.name }
});
counter++;
if (counter % 500 === 0) {
batch.execute(function(err, r) {
// do something with result
});
// Re-initialize batch
batch = col.initializeOrderedBulkOp();
}
});
if (counter % 1000 != 0 ){
batch.execute(function(err, r) {
// do something with result
});
}
});