Update operators

Last reviewed May 28, 2026 Content v20260528

Track mode

none

Means

Read / quiz

Reading

~1 min

Level

intermediate

This lesson

This lesson teaches Update operators: document modeling, query operators, and aggregation patterns for MongoDB.

Teams query Update operators on every MongoDB codebase—skipping it leaves gaps in debugging and data reviews.

You will apply Update operators in contexts like: Content catalogs, event logs, mobile sync backends, and polyglot stacks beside SQL services.

Copy JavaScript shell queries from each lesson into mongosh or MongoDB Atlas Data Explorer—inspect matched documents and explain plans. The in-browser lab (execution_profile: none) ships later; mongosh is the practice path now.

When you can explain the previous lesson's ideas without copying example queries verbatim.

updateOne/updateMany with $set, $inc, $push, $pull, $unset, and upsert.

Field updates

db.products.updateOne(
  { sku: 'A1' },
  { $set: { price: 8.99 }, $inc: { views: 1 } }
)

Practice: Use practice database in mongosh.

Array updates

db.products.updateOne(
  { sku: 'A1' },
  { $push: { tags: 'featured' }, $pull: { tags: 'sale' } }
)

Upsert

db.counters.updateOne(
  { _id: 'orders' },
  { $inc: { seq: 1 } },
  { upsert: true }
)

Important interview questions and answers

Q: replaceOne vs update?
A: replaceOne overwrites entire document except _id.
Q: upsert?
A: Creates doc if filter matches nothing—great for counters, risky without care.

Self-check

Increment views by 1.
When is upsert appropriate?

Pitfall: upsert:true on loose filters can create accidental documents.

Interview prep

$inc?: Increments numeric field atomically.
upsert?: Inserts if no match on filter.

Discussion

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Starter discussion topics

upsert risk?
$inc atomic?

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