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db.collection.updateOne(
{ _id: 1 },
{ $set: { name: "Alice", age: 30 } }
)| Step | Document Before | $set Fields | Document After | Action |
|---|---|---|---|---|
| 1 | { _id: 1, name: "Bob", city: "NY" } | { name: "Alice", age: 30 } | { _id: 1, name: "Alice", city: "NY", age: 30 } | Updated 'name', added 'age' |
| 2 | { _id: 2, city: "LA" } | { name: "Alice", age: 30 } | { _id: 2, city: "LA", name: "Alice", age: 30 } | Added 'name' and 'age' |
| 3 | { _id: 3, name: "Charlie", age: 25 } | { age: 30 } | { _id: 3, name: "Charlie", age: 30 } | Updated 'age' only |
| 4 | N/A | N/A | N/A | No more documents to update, operation ends |
| Document _id | Before $set | After $set |
|---|---|---|
| 1 | { name: "Bob", city: "NY" } | { name: "Alice", city: "NY", age: 30 } |
| 2 | { city: "LA" } | { city: "LA", name: "Alice", age: 30 } |
| 3 | { name: "Charlie", age: 25 } | { name: "Charlie", age: 30 } |
$set operator updates fields in a MongoDB document.
It replaces existing field values or adds new fields if missing.
Syntax: { $set: { field1: value1, field2: value2 } }
Used in update operations like updateOne or updateMany.
Does not remove fields, only sets or adds.$set operator do in MongoDB?$set$set operator is used to update existing fields or add new fields in a MongoDB document without affecting other fields.$unset, replacing documents uses replaceOne, and creating collections is unrelated to $set.$set updates or adds fields [OK]age to 30 in a document using $set?$set syntax$set operator requires an object with field-value pairs inside curly braces: {$set: {field: value}}.$set syntax uses object with field-value pairs [OK]{ name: 'Alice', city: 'Paris' }, what will be the document after running db.users.updateOne({name: 'Alice'}, {$set: {city: 'London', age: 25}})?$set effect on fields$set operator updates existing fields and adds new fields without removing others.city changes from 'Paris' to 'London', and new field age with value 25 is added. The name field remains unchanged.$set updates and adds fields, keeps others [OK]db.products.updateOne({id: 101}, {$set: {price: 20, stock}}). What is the problem?$set operator requires each field to have a value. Here, stock is listed without a value, which is invalid syntax.employees collection to add a new field status with value 'active' only if the field status does not already exist. Which update command using $set is correct?