How do I update sub document with "save" function in mongoose?

Question

My questions is bit naive but I could not find an answer after searching everywhere.

I have a schema of user

name: {type:String},
relations: [{
    entity: mongoose.Schema.Types.ObjectId,
    year: {type:Number}
}]

I want to update the year of a user with relations.entity = R1

I am able to update it with an update function

var toupdate = {}
toupdate["relations.$.year"] = 1900;

User.update({'relations.entity': 'R1'},{"$set": toupdate},
    function(err,results){
    // console.log(results);
});

While this works well, I want to use .save() method as I have other fields that are already being updated above.

User.find({_id:"myid"},function(err,user){
    user.name = "my new name";

    // find the relation matching the relations.entity = "R1"

    user.save(function(err,results){
        // send my results returned
    });
})

How do I write the logic before calling save()?

Answer 1

var year = 1900;
var entity = "R1"

User.find({_id:"myid"},function(err,user){
    user.name = "my new name";
    if ( user.relations && Object.prototype.toString.call( user.relations ) === '[object Array]' ) {
       user.relations.forEach( (relation, index , relations) => { 
          if(relation.entity === entity  ) {
             relations[index].year = year;
          }
       })
    }
    // find the relation matching the relations.entity = "R1"

    user.save(function(err,results){
        // send my results returned
    });
})

For multi relation update you can change entity to array and using indexOf to update the year.

Answer 2

User.findOne({_id:"myid"},function(err,user){
  user.name = "my new name";
  var tmp = user.relations;
  _.forEach(tmp,function(aObj){
    if(aObj.entity == 'R'){
      aObj.year = 1900;
    }
  });
  user.relations = tmp;
  user.save(function(err,results){
  });
});