Hello
This updated the documents where $mystring=“a”,and to “a Updated”.
Using the $function,i runned it on mongo shell
> use testdb
switched to db testdb
> db.testcoll.drop()
true
> db.testcoll.insert([{"_id":1,"mystring":"a"},{"_id":2,"mystring":"b"},{"_id":3,"mystring":"c"},{"_id":4,"mystring":"a"}]);
BulkWriteResult({
"writeErrors" : [ ],
"writeConcernErrors" : [ ],
"nInserted" : 4,
"nUpserted" : 0,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"upserted" : [ ]
})
> db.testcoll.find();
{ "_id" : 1, "mystring" : "a" }
{ "_id" : 2, "mystring" : "b" }
{ "_id" : 3, "mystring" : "c" }
{ "_id" : 4, "mystring" : "a" }
> db.testcoll.updateMany({"mystring" : "a"},[{"$addFields":{"mystring":{"$function":{"args":["$mystring"],"lang":"js","body":"function mypush(s) { return s+\" Updated\";}"}}}}]);
{ "acknowledged" : true, "matchedCount" : 2, "modifiedCount" : 2 }
>
> db.testcoll.find();
{ "_id" : 1, "mystring" : "a Updated" }
{ "_id" : 2, "mystring" : "b" }
{ "_id" : 3, "mystring" : "c" }
{ "_id" : 4, "mystring" : "a Updated" }
I tested on updating array also,its the same way,it worked fine,i used push.
This is how it works,but pipeline update are different from the old updates way.
With pipeline the result of the pipeline is the new document you want.