Updating a specific element in an array with MongoDB / Meteor

Question

"users_voted" : [ 
    {
        "user_id" : "AQG8ECLdBRJ4jwPMG",
        "score" : "down"
    }
]

Wondering how I would go about updating the users_voted field which is an array objects. I need to have a specific object updated. I know the index at which this object is located, I simply need to figure out how I can update that object in a MongoDB / Meteor collection.

This is some pseudo-code that I have to better explain what I mean.

Posts.update({_id: post_id}, {$set: {vote_score[index]: u_object}});

So in this query I know index and post_id as well as u_object is the object that I am trying to put into the array in place of whatever object that was there at that index. If someone could help let me know how I should go about this, it would be great.

David Weldon · Accepted Answer · 2014-03-21 20:31:16Z

8

You can't use variables as keys in an object literal. Give this a try:

var obj = {};
obj["users_voted." + index] = u_object;
Posts.update({_id: post_id}, {$set: obj});

answered Mar 21, 2014 at 20:31

David Weldon

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6 Comments

Maaz Over a year ago

It's not an object. It's an array of objects. I want to update a single object in that array. I have the index of that object in the array. What query should I use to update it? I do not want to get the whole array, add the object and then update the whole array.

Maaz Over a year ago

and I should be able to use a variable as an index for an array. Again, I am aware that the code I provided is likely wrong (pseudo-code). I should have been more clear, sorry about that.

David Weldon Over a year ago

Sorry I think my phrasing was confusing - I was referring to the key in your pseudo-code: vote_score[index]. I'm not sure what vote_score is (maybe a typo). Anyway, the code I provided should update the users_voted array at the position specified by index with the value contained in u_object. If that isn't what you want, let me know.

user1952811 Over a year ago

This is working. Thanks! Also how can I remove the element from the array entirely, if I know the index of the element? Possibly using $pull?

David Weldon Over a year ago

Check out the answers to this question - it looks like you can use $pull but only by value (not by index). So: Posts.update({_id: post_id}, {$pull: {'users_voted': u_object}});

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