The best way to do this is in version 4.2+ which allows using of aggregation pipeline in the update document and the updateOne
, updateMany
or update
collection methods. Note that the latter has been deprecated in most if not all languages drivers.
MongoDB 4.2+
Version 4.2 also introduced the $set
pipeline stage operator which is an alias for $addFields
. I will use $set
here as it maps with what we are trying to achieve.
db.collection.<update method>(
{},
[
{"$set": {"name": { "$concat": ["$firstName", " ", "$lastName"]}}}
]
)
Note that square brackets in the second argument to the method which defines an aggregation pipeline instead of a plain update document. Using a plain document will not work correctly.
MongoDB 3.4+
In 3.4+ you can use $addFields
and the $out
aggregation pipeline operators.
db.collection.aggregate(
[
{ "$addFields": {
"name": { "$concat": [ "$firstName", " ", "$lastName" ] }
}},
{ "$out": "collection" }
]
)
Note that this does not update your collection but instead replaces the existing collection or creates a new one. Also for update operations that require “typecasting” you will need client-side processing, and depending on the operation, you may need to use the find()
method instead of the .aggreate()
method.
MongoDB 3.2 and 3.0
The way we do this is by $project
ing our documents and using the $concat
string aggregation operator to return the concatenated string.
From there, you then iterate the cursor and use the $set
update operator to add the new field to your documents using bulk operations for maximum efficiency.
Aggregation query:
var cursor = db.collection.aggregate([
{ "$project": {
"name": { "$concat": [ "$firstName", " ", "$lastName" ] }
}}
])
MongoDB 3.2 or newer
from this, you need to use the bulkWrite
method.
var requests = [];
cursor.forEach(document => {
requests.push( {
'updateOne': {
'filter': { '_id': document._id },
'update': { '$set': { 'name': document.name } }
}
});
if (requests.length === 500) {
//Execute per 500 operations and re-init
db.collection.bulkWrite(requests);
requests = [];
}
});
if(requests.length > 0) {
db.collection.bulkWrite(requests);
}
MongoDB 2.6 and 3.0
From this version, you need to use the now deprecated Bulk
API and its associated methods.
var bulk = db.collection.initializeUnorderedBulkOp();
var count = 0;
cursor.snapshot().forEach(function(document) {
bulk.find({ '_id': document._id }).updateOne( {
'$set': { 'name': document.name }
});
count++;
if(count%500 === 0) {
// Excecute per 500 operations and re-init
bulk.execute();
bulk = db.collection.initializeUnorderedBulkOp();
}
})
// clean up queues
if(count > 0) {
bulk.execute();
}
MongoDB 2.4
cursor["result"].forEach(function(document) {
db.collection.update(
{ "_id": document._id },
{ "$set": { "name": document.name } }
);
})