Bulk write operations in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this bulkWrite operation?

Consider a MongoDB collection products with documents:

[{ _id: 1, name: "Pen", stock: 10 }, { _id: 2, name: "Pencil", stock: 5 }]

What will be the result of this bulkWrite operation?

db.products.bulkWrite([
  { updateOne: { filter: { _id: 1 }, update: { $inc: { stock: 5 } } } },
  { updateOne: { filter: { _id: 2 }, update: { $set: { stock: 0 } } } }
])

MongoDB

db.products.bulkWrite([
  { updateOne: { filter: { _id: 1 }, update: { $inc: { stock: 5 } } } },
  { updateOne: { filter: { _id: 2 }, update: { $set: { stock: 0 } } } }
])

A {"nMatched":2,"nModified":2,"ok":1}

B {"nMatched":1,"nModified":1,"ok":1}

C {"nMatched":2,"nModified":1,"ok":1}

D {"nMatched":1,"nModified":2,"ok":1}

💡 Hint

Each updateOne matches one document and modifies it.

Both updateOne operations match one document each (_id 1 and 2). Both modify the stock field, so nMatched and nModified are 2.

📝 Syntax

intermediate

Which bulkWrite syntax is valid to insert two new documents?

Choose the correct bulkWrite syntax to insert two new documents into a MongoDB collection.

A db.collection.bulkWrite([{ insertOne: { doc: { name: "A" } } }, { insertOne: { doc: { name: "B" } } }])

B db.collection.bulkWrite([{ insertOne: { document: { name: "A" } } }, { insertOne: { document: { name: "B" } } }])

C db.collection.bulkWrite([{ insertOne: { document: { name: "A" } } }, { insertMany: { documents: [{ name: "B" }] } }])

D db.collection.bulkWrite([{ insert: { document: { name: "A" } } }, { insert: { document: { name: "B" } } }])

💡 Hint

The correct key for inserting a single document is insertOne with document field.

Option B uses the correct insertOne operation with document key. Options A and B use invalid keys. Option B mixes insertOne and insertMany which is valid in bulkWrite.

❓ optimization

advanced

How to optimize bulkWrite for mixed inserts and updates?

You want to insert 100 new documents and update 50 existing documents in one bulkWrite operation. Which approach is best for performance?

A Use one bulkWrite with 150 operations mixing insertOne and updateOne commands.

B Run 100 insertMany operations separately, then 50 updateOne operations separately.

C Use separate bulkWrite calls: one for all inserts, one for all updates.

D Use a single updateMany operation for all updates and insertOne for each insert.

💡 Hint

bulkWrite supports mixing different operation types in one call.

Option A uses one bulkWrite call with all operations mixed, reducing network overhead and improving performance. Options B and C cause multiple calls. Option A is invalid because updateMany cannot update different documents with different filters in one call.

🔧 Debug

advanced

Why does this bulkWrite operation fail with a syntax error?

Identify the syntax error in this bulkWrite command:

db.collection.bulkWrite([
  { updateOne: { filter: { _id: 1 }, update: { $set: { name: "X" } } } },
  { insertOne: { document: { name: "Y" } }
])

MongoDB

db.collection.bulkWrite([
  { updateOne: { filter: { _id: 1 }, update: { $set: { name: "X" } } } },
  { insertOne: { document: { name: "Y" } }
])

A Invalid use of $set operator in updateOne.

B Missing comma between updateOne and insertOne operations.

C Using bulkWrite without a callback causes syntax error.

D Missing closing brace '}' for the insertOne operation object.

💡 Hint

Check the braces and commas carefully in the array of operations.

The insertOne operation object is missing a closing brace '}', causing a syntax error. The comma between operations is present. $set is valid. bulkWrite can be used without callback in modern drivers.

🧠 Conceptual

expert

What happens if an unordered bulkWrite operation fails midway?

You run a bulkWrite with ordered: false containing 10 operations. The 5th operation fails due to a duplicate key error. What is the behavior of the remaining operations?

A Only operations before the failure run; operations after are skipped.

B Execution stops immediately after the failure; remaining operations are not run.

C All other operations continue to execute despite the failure.

D The entire bulkWrite is rolled back; no changes are applied.

💡 Hint

Consider the difference between ordered and unordered bulkWrite behavior.

With ordered: false, bulkWrite continues executing all operations even if some fail. Only the failed operations are reported as errors. With ordered: true, execution stops at the first failure.