How do I partially update an object in MongoDB so

Question

Given this document saved in MongoDB

{
   _id : ...,
   some_key: { 
        param1 : "val1",
        param2 : "val2",
        param3 : "val3"
   }
}

An object with new information on param2 and param3 from the outside world needs to be saved

var new_info = {
    param2 : "val2_new",
    param3 : "val3_new"
};

I want to merge / overlay the new fields over the existing state of the object so that param1 doesn't get removed

Doing this

db.collection.update(  { _id:...} , { $set: { some_key : new_info  } } 

Will lead to MongoDB is doing exactly as it was asked, and sets some_key to that value. replacing the old one.

{
   _id : ...,
   some_key: { 
      param2 : "val2_new",
      param3 : "val3_new"
   }
}

What is the way to have MongoDB update only new fields (without stating them one by one explicitly)? to get this:

{
   _id : ...,
   some_key: { 
        param1 : "val1",
        param2 : "val2_new",
        param3 : "val3_new"
   }
}

I'm using the Java client, but any example will be appreciated

Answer 1

In Mongo 3.6 there is a function mergeObjects doing exactly what you need:

https://docs.mongodb.com/manual/reference/operator/aggregation/mergeObjects/

Answer 2

I had success doing it this way:

db.collection.update(  { _id:...} , { $set: { 'key.another_key' : new_info  } } );

I have a function that handles my profile updates dynamically

function update(prop, newVal) {
  const str = `profile.${prop}`;
  db.collection.update( { _id:...}, { $set: { [str]: newVal } } );
}

Note: 'profile' is specific to my implementation, it is just the string of the key that you would like to modify.

Answer 3

Yeah, the best way is to convert the object notation to a flat key-value string representation, as mentioned in this comment: https://stackoverflow.com/a/39357531/2529199

I wanted to highlight an alternative method using this NPM library: https://www.npmjs.com/package/dot-object which lets you manipulate different objects using dot notation.

I used this pattern to programatically create a nested object property when accepting the key-value as a function variable, as follows:

const dot = require('dot-object');

function(docid, varname, varvalue){
  let doc = dot.dot({
      [varname]: varvalue 
  });

  Mongo.update({_id:docid},{$set:doc});
}

This pattern lets me use nested as well as single-level properties interchangeably, and insert them cleanly into Mongo.

If you need to play around with JS Objects beyond just Mongo, especially on the client-side but have consistency when working with Mongo, this library gives you more options than the earlier mentioned mongo-dot-notation NPM module.

P.S I originally wanted to just mention this as a comment but apparently my S/O rep isn't high enough to post a comment. So, not trying to muscle in on SzybkiSasza's comment, just wanted to highlight providing an alternative module.

Answer 4

    // where clause DBObject
    DBObject query = new BasicDBObject("_id", new ObjectId(id));

    // modifications to be applied
    DBObject update = new BasicDBObject();

    // set new values
    update.put("$set", new BasicDBObject("param2","value2"));

   // update the document
    collection.update(query, update, true, false); //3rd param->upsertFlag, 4th param->updateMultiFlag

If you have multiple fields to be updated

        Document doc = new Document();
        doc.put("param2","value2");
        doc.put("param3","value3");
        update.put("$set", doc);

Answer 5

Mongo lets you update nested documents using a . convention. Take a look: Updating nested documents in mongodb. Here's another question from the past about a merge update, like the one you're looking for I believe: MongoDB atomic update via 'merge' document

Answer 6

You can use dot-notation to access and set fields deep inside objects, without affecting the other properties of those objects.

Given the object you specified above:

> db.test.insert({"id": "test_object", "some_key": {"param1": "val1", "param2": "val2", "param3": "val3"}})
WriteResult({ "nInserted" : 1 })

We can update just some_key.param2 and some_key.param3:

> db.test.findAndModify({
... query: {"id": "test_object"},
... update: {"$set": {"some_key.param2": "val2_new", "some_key.param3": "val3_new"}},
... new: true
... })
{
    "_id" : ObjectId("56476e04e5f19d86ece5b81d"),
    "id" : "test_object",
    "some_key" : {
        "param1" : "val1",
        "param2" : "val2_new",
        "param3" : "val3_new"
    }
}

You can delve as deep as you like. This is also useful for adding new properties to an object without affecting the existing ones.