Dynamically create Meteor.js MongoDB query

Question

For some reason I'm having a hard time getting this to work. I have a Mongo collection called 'cats', and another called 'rows'. The cat field in 'cats' is currentCat. Then I want to be able to update a document in 'rows' by referring to a preexisting document with an _id. No problems there. But for every currentCat, I want to add an element to the 'rows' document with currentCat as the field and something else as the value (currentPer). I came up with this:

var cats = Cats.find({owner: Meteor.userId()}, {fields: {cat: 1, per: 1}});

cats.forEach(function(cats) { //Inserts the rest of the row
  var currentCat = cats['cat'];
  var currentPer = cats['per'];
  var currentAmount = Math.round(amount*currentPer*100)/100;

  Rows.update(
    { _id: row },
    { $push: { currentCat: currentAmount } }
  );
});

(row is the id of the document I want modified)

Of course, it doesn't work as expected and just inserts ...{currentCat: 57} instead of the value of the variable currentCat. Next, I tried creating a query object (as described here):

var query = ({ _id: row }, { $push: { currentCat: currentAmount } })

That also failed, but this time with a wonderfully descriptive error message:

Error: Invalid modifier. Modifier must be an object.

Any help would be appreciated, as I've spent hours and countless Google searches on this (although the answer is probably obvious and I just can't see it - I'm still trying to get used to Meteor after PHP).

EDIT: I want the finished document to look something like this:

 { "_id" : "PshEYKebccw7eYaTo", 
   "createdAt" : ISODate("2014-11-26T00:52:51.840Z"),
   "cat1" : 312,
   "cat2" : 564,
   "owner" : "GiWCb8jXbPfzyc5ZF",
   "text" : "asdf" 
}

What do you want a Row document to look like? Based on your code, I'm expecting something like {_id: 123, currentCat: [5.25, 6.75, 1.55, 2.78]} — colllin
– colllin, Commented Nov 26, 2014 at 2:15
@Colllin Please see my example. I want to have a field and value pair for each cat. — Max Isom
– Max Isom, Commented Nov 26, 2014 at 2:25
Ok, so basically you missed the point of the query object in that other answer. In Javascript, { currentCat: currentAmount } becomes { 'currentCat': 312 } because the key must be a literal key. You can't use a variable as the key name. In order to do that, you must build up the object as in my answer below. By using the square bracket notation, you can set a dynamic key on the object, and then send that object into the query. catData[currentCat] first interprets the currentCat variable to be 'cat1', and then accesses that key, as if you had done catData['cat1']. — colllin
– colllin, Commented Nov 26, 2014 at 2:40

colllin · Accepted Answer · 2014-11-26 02:31:34Z

2

$push is only for operating on arrays. Based on your example of a Row document, you don't really want an array operation here.

Try just setting fields on the Row document for each new cat value.

  var catData = {};
  catData[currentCat] = currentAmount;
  // As an example, catData now looks like {'cat1': 312}

  Rows.update(
    { _id: row },
    { $set: catData }
  );

answered Nov 26, 2014 at 2:31

colllin

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1 Comment

Max Isom Over a year ago

Thanks! Now works perfectly. I ended up declaring catData before the forEach and put Rows.update() after. Also, as a bonus, I now only access the database once instead of multiple times for each cat.

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