Upsert behavior (update or insert) in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to perform an upsert operation in MongoDB.

MongoDB

db.collection.updateOne({ _id: 1 }, { $set: { name: 'Alice' } }, { [1]: true })

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

Aupdate

Bupsert

Cinsert

Dreplace

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'insert' instead of 'upsert' causes an error because 'insert' is not a valid option here.

Omitting the option means no insert will happen if no document matches.

The upsert option tells MongoDB to insert a new document if no matching document is found during the update.

2fill in blank

medium

Complete the code to update a document or insert it if it does not exist.

MongoDB

db.users.updateOne({ username: 'bob' }, { $set: { age: 30 } }, { [1]: true })

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

Areplace

Bmulti

Cinsert

Dupsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'replace' will replace the whole document but does not insert if missing.

Using 'multi' is invalid for updateOne.

The upsert option ensures the document is inserted if it does not exist.

3fill in blank

hard

Fix the error in the upsert operation code.

MongoDB

db.products.updateOne({ sku: '123' }, { $set: { price: 20 } }, { [1]: true })

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

Aupdate

Binsert

Cupsert

Dmulti

Attempts:

3 left

💡 Hint

Common Mistakes

Setting 'upsert' to a string instead of boolean causes the operation to fail.

Using 'insert' as an option name is invalid.

The upsert option must be a boolean true, not a string like 'yes'.

4fill in blank

hard

Fill both blanks to create an upsert that sets the field and returns the updated document.

MongoDB

db.inventory.updateOne({ item: 'pencil' }, { [1]: { qty: 50 } }, { [2]: true, returnDocument: 'after' })

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

A$set

Bupsert

C$inc

Dmulti

Attempts:

3 left

💡 Hint

Common Mistakes

Using '$inc' instead of '$set' changes the value by incrementing instead of setting.

Omitting 'upsert' option means no insert will happen.

Use $set to update the field and upsert: true to insert if missing.

5fill in blank

hard

Fill all three blanks to perform an upsert that increments a count, sets a status, and enables upsert.

MongoDB

db.stats.updateOne({ user: 'john' }, { [1]: { count: 1 }, [2]: { status: 'active' } }, { [3]: true })

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

A$inc

B$set

Cupsert

D$unset

Attempts:

3 left

💡 Hint

Common Mistakes

Using '$unset' removes fields instead of updating.

Omitting 'upsert' option disables insert on no match.

Use $inc to increase count, $set to update status, and upsert: true to insert if missing.

Practice

1. What does the upsert option do in a MongoDB updateOne operation?

easy

A. It only inserts a new document without updating existing ones.

B. It updates a document if it exists, or inserts a new one if it does not.

C. It deletes a document if it exists, otherwise does nothing.

D. It duplicates the document regardless of existence.

Solution

1. Step 1: Understand the upsert option

   The upsert option in MongoDB means update if found, insert if not found.

2. Step 2: Apply to updateOne operation

   When using updateOne with upsert: true, MongoDB updates the matching document or inserts a new one if none matches.

3. Final Answer:

   It updates a document if it exists, or inserts a new one if it does not. -> Option B

4. Quick Check:

   Upsert = update or insert [OK]

Hint: Upsert means update if found, else insert new [OK]

Common Mistakes:

• Thinking upsert only inserts without updating
• Confusing upsert with delete operation
• Assuming upsert duplicates documents

2. Which of the following is the correct syntax to perform an upsert using updateOne in MongoDB?

easy

A. db.collection.updateOne(filter, update, {update: true})

B. db.collection.updateOne(filter, update, {insert: true})

C. db.collection.updateOne(filter, update, {upsert: true})

D. db.collection.updateOne(filter, update, {replace: true})

Solution

1. Step 1: Recall the updateOne method parameters

   The updateOne method takes a filter, an update document, and an options object.

2. Step 2: Identify the correct option for upsert

   The option to enable upsert is {upsert: true}, which tells MongoDB to insert if no match is found.

3. Final Answer:

   db.collection.updateOne(filter, update, {upsert: true}) -> Option C

4. Quick Check:

   Use upsert: true in options [OK]

Hint: Use {upsert: true} in updateOne options [OK]

Common Mistakes:

• Using {insert: true} instead of {upsert: true}
• Omitting the options object entirely
• Confusing update with replace option

3. Given the collection users with documents:
{ _id: 1, name: "Alice", age: 25 }
What will be the result after running:

db.users.updateOne({ _id: 2 }, { $set: { name: "Bob", age: 30 } }, { upsert: true })

and then querying db.users.find().toArray()?

medium

A. [{ _id: 1, name: "Alice", age: 25 }, { _id: 2, name: "Bob", age: 30 }]

B. [{ _id: 1, name: "Alice", age: 25 }]

C. [{ _id: 2, name: "Bob", age: 30 }]

D. []

Solution

1. Step 1: Understand the updateOne with upsert

   The filter looks for _id: 2, which does not exist, so upsert inserts a new document with _id: 2 and the given fields.

2. Step 2: Check existing documents

   The original document with _id: 1 remains unchanged, so the collection now has two documents.

3. Final Answer:

   [{ _id: 1, name: "Alice", age: 25 }, { _id: 2, name: "Bob", age: 30 }] -> Option A

4. Quick Check:

   Upsert inserts missing document, keeps existing [OK]

Hint: Upsert inserts new if filter misses existing docs [OK]

Common Mistakes:

• Assuming existing documents get deleted
• Thinking upsert only updates existing documents
• Expecting only the new document after upsert

4. You run the following code but it does not insert a new document when no match is found:

db.products.updateOne({ sku: "123" }, { price: 19.99 })

What is the likely error?

medium

A. The filter syntax is incorrect and causes a syntax error.

B. MongoDB does not support upsert with updateOne.

C. The update document is missing the $set operator.

D. Missing the upsert: true option in the updateOne call.

Solution

1. Step 1: Check the updateOne parameters

   The updateOne call lacks the options object with upsert: true, so it only updates existing documents.

2. Step 2: Confirm upsert behavior

   Without upsert: true, no new document is inserted if the filter finds no match.

3. Final Answer:

   Missing the upsert: true option in the updateOne call. -> Option D

4. Quick Check:

   Upsert option needed to insert new docs [OK]

Hint: Add {upsert: true} to updateOne options to insert [OK]

Common Mistakes:

• Forgetting to add upsert option
• Confusing missing $set with upsert behavior
• Believing updateOne cannot upsert

5. You want to update the status field to "active" for a user with email: "[e-mail]". If no such user exists, insert a new document with email and status. Which MongoDB command correctly achieves this?

hard

A. db.users.updateOne({ email: "[e-mail]" }, { $set: { status: "active" } }, { upsert: true })

B. db.users.insertOne({ email: "[e-mail]", status: "active" })

C. db.users.updateOne({ email: "[e-mail]" }, { status: "active" }, { upsert: true })

D. db.users.updateMany({ email: "[e-mail]" }, { $set: { status: "active" } })

Solution

1. Step 1: Identify the correct update syntax with upsert

   To update or insert, use updateOne with a filter, an update using $set, and {upsert: true} option.

2. Step 2: Check each option

   db.users.updateOne({ email: "[e-mail]" }, { $set: { status: "active" } }, { upsert: true }) uses $set and upsert correctly. db.users.insertOne({ email: "[e-mail]", status: "active" }) only inserts, no update. db.users.updateOne({ email: "[e-mail]" }, { status: "active" }, { upsert: true }) misses $set operator, which replaces the whole document incorrectly. db.users.updateMany({ email: "[e-mail]" }, { $set: { status: "active" } }) updates many but no upsert.

3. Final Answer:

   db.users.updateOne({ email: "[e-mail]" }, { $set: { status: "active" } }, { upsert: true }) -> Option A

4. Quick Check:

   Use updateOne + $set + upsert: true [OK]

Hint: Use $set with upsert: true in updateOne to update or insert [OK]

Common Mistakes:

• Omitting $set causing document replacement
• Using insertOne which does not update
• Forgetting upsert option for insert fallback