How to update a subdocument in mongodb - mongodb

Question

I know the question have been asked many times, but I can't figure out how to update a subdocument in mongo.
Here's my Schema:
// Schemas
var ContactSchema = new mongoose.Schema({
first: String,
last: String,
mobile: String,
home: String,
office: String,
email: String,
company: String,
description: String,
keywords: []
});
var UserSchema = new mongoose.Schema({
email: {
type: String,
unique: true,
required: true
},
password: {
type: String,
required: true
},
contacts: [ContactSchema]
});
My collection looks like this:
db.users.find({}).pretty()
{
"_id" : ObjectId("5500b5b8908520754a8c2420"),
"email" : "test#random.org",
"password" : "$2a$08$iqSTgtW27TLeBSUkqIV1SeyMyXlnbj/qavRWhIKn3O2qfHOybN9uu",
"__v" : 8,
"contacts" : [
{
"first" : "Jessica",
"last" : "Vento",
"_id" : ObjectId("550199b1fe544adf50bc291d"),
"keywords" : [ ]
},
{
"first" : "Tintin",
"last" : "Milou",
"_id" : ObjectId("550199c6fe544adf50bc291e"),
"keywords" : [ ]
}
]
}
Say I want to update subdocument of id 550199c6fe544adf50bc291e by doing:
db.users.update({_id: ObjectId("5500b5b8908520754a8c2420"), "contacts._id": ObjectId("550199c6fe544adf50bc291e")}, myNewDocument)
with myNewDocument like:
{ "_id" : ObjectId("550199b1fe544adf50bc291d"), "first" : "test" }
It returns an error:
db.users.update({_id: ObjectId("5500b5b8908520754a8c2420"), "contacts._id": ObjectId("550199c6fe544adf50bc291e")}, myNewdocument)
WriteResult({
"nMatched" : 0,
"nUpserted" : 0,
"nModified" : 0,
"writeError" : {
"code" : 16837,
"errmsg" : "The _id field cannot be changed from {_id: ObjectId('5500b5b8908520754a8c2420')} to {_id: ObjectId('550199b1fe544adf50bc291d')}."
}
})
I understand that mongo tries to replace the parent document and not the subdocument, but in the end, I don't know how to update my subdocument.

Answer 1

You need to use the $ operator to update a subdocument in an array
Using contacts.$ will point mongoDB to update the relevant subdocument.
db.users.update({_id: ObjectId("5500b5b8908520754a8c2420"),
"contacts._id": ObjectId("550199c6fe544adf50bc291e")},
{"$set":{"contacts.$":myNewDocument}})
I am not sure why you are changing the _id of the subdocument. That is not advisable.
If you want to change a particular field of the subdocument use the contacts.$.<field_name> to update the particular field of the subdocument.