How do I add an array of elements in MongoDB to an array in an existing document?

Question

In MongoDB, I'm trying to write a query to add elements from an array to an existing document, but instead of adding the elements as objects:

property: ObjectID(xxx)

the elements are getting added as just

ObjectID(xxx)

Forgive me if I get the terminology wrong. I'm completely new to MongoDB; I normally only work with relational databases. How do I properly add these new elements?

I have a collection called auctions which has two fields: ID and properties. Properties is an array of objects named property. Here's an example with two auction documents:

** I changed the object IDs to make them easier to reference in our discussion

Collection db.auctions
{
    "_id" : ObjectId("abc"),
    "properties" : [
        {
            "property" : ObjectId("prop1")
        }, 
        {
            "property" : ObjectId("prop2")
        }, 
        {
            "property" : ObjectId("prop3")
        }]
}
{
    "_id" : ObjectId("def"),
    "properties" : [
        {
            "property" : ObjectId("prop97")
        }, 
        {
            "property" : ObjectId("prop98")
        }]
}

I want to add 3 new properties to auction "abc". How do I do this?

Here's is what I tried:

I have an array of properties that looks like this:

Array PropsToAdd
[
    ObjectId("prop4"), 
    ObjectId("prop5"), 
    ObjectId("prop6")
]

I wrote an update query to push these properties into the properties array in auctions:

db.auctions.update(
    {"_id": "abc"}
    ,
    { $push: { properties: { $each: PropsToAdd } } } 
);

This query gave the result below. Notice that instead of adding elements named property with a value from my array, it's just added my values from my array. I obviously need to add that "property" part, but how do I do that?

Collection db.auctions (_id "abc" only)
    {
    "_id" : ObjectId("abc"),
    "properties" : [
        {
            "property" : ObjectId("prop1")
        }, 
        {
            "property" : ObjectId("prop2")
        }, 
        {
            "property" : ObjectId("prop3")
        }, 
        ObjectId("prop4"), 
        ObjectId("prop5"), 
        ObjectId("prop6"), 
        ObjectId("prop7")]
}

The result I'm looking for is this:

Collection db.auctions (_id "abc" only)
{
    "_id" : ObjectId("abc"),
    "properties" : [
        {
            "property" : ObjectId("prop1")
        }, 
        {
            "property" : ObjectId("prop2")
        }, 
        {
            "property" : ObjectId("prop3")
        }, 
        {
            "property" : ObjectId("prop4")
        },
        {
            "property" : ObjectId("prop5")
        },         
        {
            "property" : ObjectId("prop6")
        } 
}

Here is some further information on that array of properties I'm adding. I get it from running these queries. Perhaps one of them needs changed?

This query gets an array of current properties:

var oldActiveProperties = db.properties.distinct( "saleNumber", { "active": true, "auction": ObjectId("abc") } );

Then those results are used to find properties in the new file that weren't in the old file:

var PropsToAdd = db.newProperties.distinct(
    "_id"
    , { "saleNumber": { "$nin": oldActiveProperties }, "active": true}
);

The resulting array is what I need to add to the auctions collection.

chridam · Accepted Answer · 2016-04-22 15:38:37Z

3

Use the JavaScript's native map() method to map the array into an array of documents. The following shows this:

var PropsToAdd = db.newProperties.distinct("_id", 
    { "saleNumber": { "$nin": oldActiveProperties }, "active": true}
).map(function (p) { return { property: p }; });

db.auctions.update(
    {"_id": "abc"},
    { $push: { "properties": { "$each": PropsToAdd } } } 
);

answered Apr 22, 2016 at 15:38

chridam

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2 Comments

boilers222 Over a year ago

That worked great; thank you! Like I said, I'm new to MongoDB. I'm using MongoChef to write queries. Are most/all JavaScript functions available to me in writing queries?

chridam Over a year ago

MongoDB uses the JavaScript engine SpiderMonkey for both the mongo shell and for server-side javascript in mongod so the api is available when writing your queries in mongo shell although most interactions with MongoDB do not use JavaScript but use an idiomatic driver in the language of the interacting application.

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