Mongodb get unique value from documents and add to array - arrays

Question

I wanted to do a query to match documents in one collection with documents in another collection based upon a value which should be contained in both sets of documents but, as I have been informed that Mongo does not support a JOIN, I believe I can't do what I want in the way I want to.
My alternative method then is to insert a document into the collection (col1) where I want to do a query and update which contains an array of all the unique cycle number which are in the other collection (col2).
Collection 1 (Col 1)
{
"_id" : ObjectId("5670961f910e1f54662c11ag"),
"objectType" : "Account Balance",
"Customer" : "Thomas Brown",
"status" : "unprocessed",
"cycle" : "1234"
},
{
"_id" : ObjectId("5670961f910e1f54662c12fd"),
"objectType" : "Account Balance",
"Customer" : "Luke Underwood",
"status" : "unprocessed",
"cycle" : "1235"
}
Collection 2 (Col 2)
{
"_id" : ObjectId("5670961f910e1f54662c1d9d"),
"objectOrigin" : "Xero",
"Value" : "500.00",
"key" : "grossprofit",
"cycle" : "1234",
"company" : "e56e09ef-5c7c-423e-b699-21469bd2ea00"
},
{
"_id" : ObjectId("5670961f910e1f54662c1d9f"),
"objectOrigin" : "Xero",
"Value" : "500.00",
"key" : "grossprofit",
"cycle" : "1234",
"company" : "0a514db8-1428-4da6-9225-0286dc2662c1"
},
{
"_id" : ObjectId("5670961f910e1f54662c1da0"),
"objectOrigin" : "Xero",
"Value" : "-127.28",
"key" : "grossprofit",
"cycle" : "1234",
"company" : "c2d0561c-dc5d-44b9-beaf-d69a3472a2b8"
},
{
"_id" : ObjectId("5670961f910e1f54662c1da1"),
"objectOrigin" : "Xero",
"Value" : "-127.28",
"key" : "grossprofit",
"cycle" : "1235",
"company" : "c3fbe6e4-962a-45f6-9ce3-71e2a588438c"
}
So I want to create a document in collection 1 which looks like this:
{
"_id" : ObjectId("5670961f910e1f54662c1d9f"),
"objectType" : "Status Updater",
"cycles" : ["1234","1235"]
}
Now what I want to do is query ALL documents where cycle = cycles and update "status" to "processed". I believe I would do this with a findAndModify with multi : true but not entirely sure.
When finished, I will just simply delete any document in the Collection 1 where objectType is "Status Updater".

Answer 1

If I understand correctly, you want to
a) update all documents in collection #1 where the value of cycle
exists in collection #2.
b) Furthermore, your document of type "objectType" : "Status
Updater" is only a temporary document to keep track of all the cycle
values.
I think you can skip b) and just use the following (this code needs to be executed in the mongo shell):
# get values of all unique cycle values
# returns an array containing: ["1234", "1235", ...]
values = db.coll2.distinct("cycles", {})
# find all documents where cycles value is in the values array
# and update their status.
db.coll1.update({cycles: {$in: values}}, {$set: {status: "processed"}}, {multi: true})