MongoDB: Updating Documents

MongoDB: Updating Documents

Updating documents modifies existing records in a collection, keeping data current and accurate.

Why Update Documents?

• Data Evolution: Change prices, addresses, statuses.
• Correction: Fix errors or outdated info.
• Enrichment: Add new fields.
• Counters/Metrics: Increment/decrement numeric fields.
• Array Management: Add/remove elements from arrays.

Core Concepts

• Filter Document: Specifies which documents to update (like query filters).
• Update Document: Contains update operators defining modifications.
• Update Operators (must use):
  • $set: Set or add a field.
  • $inc: Increment/decrement numeric fields.
  • $unset: Remove a field.
  • $push: Add element(s) to array.
  • $pull: Remove element(s) from array.
  • $addToSet: Add element if not present.
  • $rename: Rename a field.
  • $currentDate: Set field to current date/time.

Methods

• updateOne(filter, update, options): Update a single matched document.
• updateMany(filter, update, options): Update multiple matched documents.
• replaceOne(filter, replacement, options): Replace entire document (except _id).

Options include:

• upsert: true: Insert if no match.
• arrayFilters: Conditions to update specific array elements.

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Node.js Examples

1. updateOne with $set and $inc

Update "Laptop Pro" price and decrement stock by 1.

2. updateMany with $set and $push

Change all "Peripherals" category and add "popular" tag to products with stock > 20.

3. replaceOne

Replace entire document for "External HDD".

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Key Takeaways

• updateOne() and updateMany() update specific fields using operators.
• replaceOne() substitutes the entire document (except _id).
• MongoDB updates are atomic per document.
• upsert: true is useful for conditional insert-or-update.
• Always use precise filters to avoid unintended changes.