How to check before updating an array element in MongoDB/NodeJS - arrays

Question

In my sample document, I have a campaign document that contains the _id of the document and an importData array. importData is an array of objects containing a unique date and source value.
My goal is to have an object updated with a unique date/source pair. I would like to have the new object replace any matching object. In the example below, Fred may have originally donated a TV, but I want my application to update the object to reflect he donated both a TV and a radio.
// Events (sample document)
{
"_id" : "Junky Joe's Jubilee",
"importData" : [
{
"date": "2015-05-31",
"source": "Fred",
"items": [
{item: "TV", value: 20.00},
{item: "radio", value: 5.34}
]
},
{
"date": "2015-05-31",
"source": "Mary",
"items": [
{item: "Dresser", value: 225.00}
]
}
]
}
My original thought was to do something like the code below, but not only am I updating importData with Fred's donations, I'm also blowing away anything else in the importData array:
var collection = db.collection("events");
collection.update(
{_id: "Junky Joe's Jubilee",
importData: {
date: "2015-05-31",
source: 'Fred'
},
}, // See if we can find a campaign object with this name
{
$set:
{"importData":
{
date: "2015-05-31",
source: 'Fred',
items: [
{item: "TV", value: 20.00},
{item: "radio", value: 5.34}
]
}
}
},
{upsert: true}); // Create a document if one does not exist for this campaign
When I tried pushing (instead of $set), I was getting multiple entries for the date/source combos (e.g. Fred would appear to have donated two items multiple times on "2015-05-31").
How would I go about doing that with the MongoDB native driver and NodeJS?

Answer 1

Try this
var collection = db.collection("events");
collection.update(
{_id: "Junky Joe's Jubilee",
importData: {
date: "2015-05-31",
source: 'Fred'
},
}, // See if we can find a campaign object with this name
{
$set:
{"importData.$":
{
date: "2015-05-31",
source: 'Fred',
items: [
{item: "TV", value: 20.00},
{item: "radio", value: 5.34}
]
}
}
},
{upsert: true}); // Create a document if one does not exist for this campaign
According to the documentation under Array update operators this should only modify the first element in the array, which matches the query.