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Update MongoDB field using value of another field?
You can use aggregate function to update MongoDB field using the value of another field. Here, we will create two collections:
name
studentInformation
<name> Collection
The query to create first collection with documents is as follows:
> db.name.insert({"FirstName":"John","LastName":"Smith"});
WriteResult({ "nInserted" : 1 })Now you can display all documents from the collection with the help of find() method. The query is as follows:
> db.name.find().pretty();
The following is the output that displays the collection “name” documents:
{
"_id" : ObjectId("5c6c00dd68174aae23f5ef55"),
"FirstName" : "John",
"LastName" : "Smith"
}<studentInformation> Collection
The query to create second collection with documents is as follows:
> db.studentInformation.insert({"StudentFirstName":"Carol","StudentLastName":"Taylor"});
WriteResult({ "nInserted" : 1 })Now you can display all documents from the collection with the help of find() method. The query is as follows:
> db.studentInformation.find().pretty();
The following is the output:
{
"_id" : ObjectId("5c6c013068174aae23f5ef56"),
"StudentFirstName" : "Carol",
"StudentLastName" : "Taylor"
}Now, let us update collection “name” with another collection “studentInformation”. The query is as follows:
> db.studentInformation.aggregate( [
{"$addFields":{"FullName":{"$concat":["$StudentFirstName"," ","$StudentLastName"]} }},
{"$out":"name"} ] );Now you can check the documents of the collection “name”. The query is as follows:
> db.name.find().pretty();
The following is the output that displays that we have successfully updated the fields:
{
"_id" : ObjectId("5c6c013068174aae23f5ef56"),
"StudentFirstName" : "Carol",
"StudentLastName" : "Taylor",
"FullName" : "Carol Taylor"
}
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