Replacing embedded document in array in MongoDB

Question

Is there an easy way to replace an entire embedded document in an array? Say replacing:

{
   "_id" : "2",
      "name" : "name2",
      "xyz..." : "xyz2..."
}

with:

{
   "_id" : "2",
      "name" : "name6",
      "xyz..." : "xyz5..."
      "morefields..." : "fields..."
}

Searching for _id (embedded). Or do I need to replace each field individually using $set?

{
  "_id" : "2",
  "users" : [{
      "_id" : "1",
      "name" : "name1",
      "xyz..." : "xyz1..."
    }, {
      "_id" : "2",
      "name" : "name2",
      "xyz..." : "xyz2..."
    }],
  "name" : "main name"
}

Gates VP · Accepted Answer · 2012-02-08 20:54:29Z

26

You are using the "array of objects" pattern. You can use the positional operator, it should look something like this:

coll.update( {'_id':'2', 'users._id':'2'}, {$set:{'users.$':{ "_id":2,"name":"name6",... }}}, false, true)

In my experience, the "array of objects" pattern is not optimal if the objects have a natural ID. In your case, this could be modeled as the following:

{
  "_id" : "2",
  "users" : 
    { "1" : { "name" : "name1", "xyz..." : "xyz1..." }, 
      "2" : { "name" : "name2", "xyz..." : "xyz2..." }
    }
  "name" : "main name"
}

In this case you can use the dot notation to easily update the item you want.

var newValue = {  "name" : "name6", "xyz..." : "xyz5...", "morefields..." : "fields..." };
coll.update({_id: 2}, { $set: { "users.2" : newValue } });

answered Feb 8, 2012 at 20:54

Gates VP

45.3k11 gold badges108 silver badges108 bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

Fredrik L Over a year ago

That works great, thanks! Interesting the 2nd alternative but I'm not sure it will work since I'll need to remove some entries in the middle. "users.2" is the position in the array I assume.

Fredrik L Over a year ago

I thought users.2 referred to the array position but it's actually using the id (and returning empty brackets for all other array items}, cool.

Gates VP Over a year ago

MongoDB recognizes arrays in a query. So users.2 could search through the users array looking for objects with key of 2 or it could look at the key:2 of users.

Fredrik L Over a year ago

I was going with your second model but now I'm thinking I won't be able to index the inner name field. If it was an array it would be users.name but here it's users.1.name users.2.name?

Gates VP Over a year ago

You are correct, the second structure does not index very well. This is definitely a trade-off. But you cannot optimize for all queries with MongoDB. If you want this query to be fast, then you have to trade off ease of updating.

|

Collectives™ on Stack Overflow

Replacing embedded document in array in MongoDB

1 Answer 1

9 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

9 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related