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delete-replace-mongodb

Delete and replace

Last reviewed Jun 1, 2026 Content v20260601
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none
Means
Read / quiz
Reading
~1 min
Level
intermediate

This lesson

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

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

You will apply Delete and replace 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.

deleteOne, deleteMany, and replaceOne—always preview filters with find first.

Delete

db.sessions.find({ expiresAt: { $lt: new Date() } }).limit(5)
db.sessions.deleteMany({ expiresAt: { $lt: new Date() } })

Practice: Use practice database in mongosh.

Replace

db.products.replaceOne(
  { sku: 'A1' },
  { sku: 'A1', name: 'Widget v2', price: 11.99, tags: [] }
)

Replace drops fields not listed—often prefer $set partial updates.

TTL index (preview)

db.sessions.createIndex({ expiresAt: 1 }, { expireAfterSeconds: 0 })

MongoDB deletes docs when expiresAt time passes—handy for sessions.

Important interview questions and answers

  1. Q: deleteMany empty filter?
    A: Deletes entire collection—guard in shell and apps.
  2. Q: replaceOne pitfall?
    A: Accidentally removes fields not included in replacement doc.

Self-check

  1. Safe order before deleteMany?
  2. TTL index use case?

Tip: TTL indexes automate session cleanup—set expiresAt as Date.

Interview prep

replaceOne risk?
Drops fields not in replacement document.
TTL index?
Auto-deletes docs when date field passes.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Not saved yet.

Check yourself

Multiple choice — immediate feedback.

Discussion

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Starter discussion topics

  • replaceOne pitfall?
  • TTL sessions?

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