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

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.

Answer 1

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 } } }
);