$out and $merge for writing results in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to write the aggregation results to a new collection using $out.

MongoDB

db.sales.aggregate([{ $group: { _id: "$item", total: { $sum: "$quantity" } } }, { $[1]: "totalSales" }])

Drag options to blanks, or click blank then click option'

Amerge

Bmatch

Cproject

Dout

Attempts:

3 left

💡 Hint

Common Mistakes

Using $merge instead of $out when the goal is to replace the entire collection.

Using $project or $match which do not write results to collections.

The $out stage writes the aggregation results to a specified collection, replacing it if it exists.

2fill in blank

medium

Complete the code to merge aggregation results into an existing collection without replacing it.

MongoDB

db.orders.aggregate([{ $group: { _id: "$customerId", totalSpent: { $sum: "$amount" } } }, { $[1]: { into: "customerTotals", on: "_id", whenMatched: "replace", whenNotMatched: "insert" } }])

Drag options to blanks, or click blank then click option'

Aout

Blookup

Cmerge

Dunwind

Attempts:

3 left

💡 Hint

Common Mistakes

Using $out which replaces the entire collection instead of merging.

Using $lookup or $unwind which are unrelated to writing results.

$merge allows merging aggregation results into an existing collection with control over matching and insertion behavior.

3fill in blank

hard

Fix the error in the aggregation pipeline to correctly write results using $merge with the right option key.

MongoDB

db.inventory.aggregate([{ $match: { status: "A" } }, { $merge: { [1]: "activeInventory" } }])

Drag options to blanks, or click blank then click option'

Ato

Binto

Ccollection

Dtarget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'to' or 'collection' which are not valid keys for $merge.

Using 'target' which is not recognized by MongoDB.

The correct option key for specifying the target collection in $merge is 'into'.

4fill in blank

hard

Fill both blanks to write aggregation results to a collection named 'summary' and replace it if it exists.

MongoDB

db.transactions.aggregate([{ $group: { _id: "$type", count: { $sum: 1 } } }, { $[1]: "[2]" }])

Drag options to blanks, or click blank then click option'

Aout

Bmerge

Csummary

Dtotals

Attempts:

3 left

💡 Hint

Common Mistakes

Using $merge instead of $out when replacement is desired.

Using wrong collection names.

$out writes results to the specified collection, replacing it. Here, 'summary' is the target collection.

5fill in blank

hard

Fill all three blanks to merge results into 'archive', matching on '_id', and updating existing documents.

MongoDB

db.logs.aggregate([{ $match: { level: "error" } }, { $[1]: { into: "[2]", on: "[3]", whenMatched: "merge", whenNotMatched: "insert" } }])

Drag options to blanks, or click blank then click option'

Amerge

Barchive

C_id

Dout

Attempts:

3 left

💡 Hint

Common Mistakes

Using $out instead of $merge for merging.

Using wrong collection or field names.

$merge stage merges documents into 'archive' collection matching on '_id' and merges existing documents.