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mongodb / Update Operations
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Update Operations

Data changes over time. A user updates their email, a product price changes, a blog post gets edited. MongoDB provides powerful update operations to modify existing documents. Let's learn how to use updateOne(), updateMany(), and replaceOne().

Update Operators

Just like query operators help you find documents, update operators help you modify them. The most common is $set, but there are many others.

OperatorDescription
$setSets the value of a field
$unsetRemoves a field
$incIncrements a numeric value
$mulMultiplies a numeric value
$renameRenames a field
$pushAdds an element to an array
$pullRemoves an element from an array

Think of update operators as editing tools. $set is like a pen that writes or changes text, $unset is like an eraser, and $inc is like a counter that ticks up or down.

updateOne() - Update First Matching Document

updateOne() updates the first document that matches the filter.
<!-- Update John's age to 31 -->
db.users.updateOne(
  { name: "John" },
  { $set: { age: 31 } }
)

Output:
{
  acknowledged: true,
  matchedCount: 1,
  modifiedCount: 1
}

updateMany() - Update All Matching Documents

updateMany() updates all documents that match the filter.
<!-- Add a "prime" field to all electronics products -->
db.products.updateMany(
  { category: "electronics" },
  { $set: { prime: true } }
)

<!-- Increase all prices by 10% -->
db.products.updateMany(
  {},
  { $mul: { price: 1.1 } }
)

Using $inc to Increment
<!-- Increase view count by 1 -->
db.posts.updateOne(
  { title: "First Post" },
  { $inc: { views: 1 } }
)

<!-- Decrease stock by 5 (use negative value) -->
db.products.updateOne(
  { name: "Laptop" },
  { $inc: { stock: -5 } }
)

Working with Arrays

$push - Add to Array
<!-- Add a new tag to a post -->
db.posts.updateOne(
  { title: "First Post" },
  { $push: { tags: "javascript" } }
)

$pull - Remove from Array
<!-- Remove a tag from a post -->
db.posts.updateOne(
  { title: "First Post" },
  { $pull: { tags: "mongodb" } }
)

replaceOne() - Replace Entire Document

Unlike updateOne() which modifies specific fields, replaceOne() replaces the entire document with a new one.
db.users.replaceOne(
  { name: "John" },
  { name: "John", email: "john.new@example.com", phone: "555-1234" }
)

Upsert - Update or Insert

Sometimes you want to update a document if it exists, or insert it if it doesn't. Use the upsert option.
<!-- If user "Jane" exists, update her age; if not, create her -->
db.users.updateOne(
  { name: "Jane" },
  { $set: { age: 28, email: "jane@example.com" } },
  { upsert: true }
)

Practical Example: Blog Post Analytics
<!-- Insert a blog post -->
db.posts.insertOne({
  title: "MongoDB Updates",
  content: "Learning about update operations...",
  views: 0,
  likes: 0,
  tags: ["mongodb", "database"]
})

<!-- Someone viewed the post -->
db.posts.updateOne(
  { title: "MongoDB Updates" },
  { $inc: { views: 1 } }
)

<!-- Someone liked the post -->
db.posts.updateOne(
  { title: "MongoDB Updates" },
  { $inc: { likes: 1 } }
)

<!-- Add a new tag -->
db.posts.updateOne(
  { title: "MongoDB Updates" },
  { $push: { tags: "nodejs" } }
)

<!-- Check the final document -->
db.posts.findOne({ title: "MongoDB Updates" })

Two Minute Drill

  • updateOne() modifies the first matching document, updateMany() modifies all matches.
  • Use $set to change field values, $inc to increment numbers.
  • Array operators: $push adds, $pull removes elements.
  • replaceOne() replaces the entire document.
  • Upsert ({ upsert: true }) creates a document if it doesn't exist.
  • Always check matchedCount and modifiedCount to confirm your update worked.
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