Sub-Operator	Description
$and	Perform a bitwise AND operation
$or	Perform a bitwise OR operation
$xor	Perform a bitwise XOR operation
$not	Perform a bitwise NOT operation

Example: Update Operators

Example 1: Using $currentDate

Imagine you have a collection of blog posts, and when editing. This timestamping operation can be assisted by the $currentDate operator.

// Before Update
db.blogPosts.findOne({ _id: postId })

// Update using $currentDate
db.blogPosts.update(
  { _id: postId },
  { $currentDate: { lastModified: true } }
)

// After Update
db.blogPosts.findOne({ _id: postId })

Output:

// Before Update
{
  _id: ObjectId("5fd0c7b86ee8a1475896a117"),
  title: "MongoDB Update Operators",
  content: "Introduction to MongoDB update operators...",
  lastModified: ISODate("2023-01-01T12:00:00Z")
}
// After Update
{
  _id: ObjectId("5fd0c7b86ee8a1475896a117"),
  title: "MongoDB Update Operators",
  content: "Introduction to MongoDB update operators...",
  lastModified: ISODate("2023-12-13T15:30:00Z")
}

Before Updates

// Retrieve a blog post with a specific ID
db.blogPosts.findOne({ _id: postId })

Before doing any editing, this line first gets a blog post from the MongoDB collection named blogPosts. It does this by looking for a document with the specific _id (a unique identifier), which each blog post has.

Update using $currentDate

// Update the "lastModified" field to the current date and time
db.blogPosts.update({ _id: postId }, { $currentDate: { lastModified: true } })

This line updates a particular post in the blogPosts collection. This update is focused on the document with a given _id (unique identifier). The update operation uses the $currentDate operator to set its value of lastModified field into current date and time. In fact, it’s like adding a time stamp to the blog post showing when it was last modified.

After Update

// Retrieve the updated blog post
db.blogPosts.findOne({ _id: postId })

Following the update, this line retrieves again to observe how things have changed. Now, the lastModified field should be set to today’s date and time so that people can see when this blog post was last altered.

Example 2 : Using $inc and $set

Consider a scenario where you have a collection of products, and you want to update the inventory count and set a new discount for a specific product.

// Before Update
db.products.findOne({ _id: productId })

// Update using $inc and $set
db.products.update(
  { _id: productId },
  {
    $inc: { inventory: -5 }, // Decrement inventory by 5 units
    $set: { discount: 0.1 }  // Set a new discount of 10%
  }
)

// After Update
db.products.findOne({ _id: productId })

Output:

// Before Update
{
  _id: ObjectId("5fd0c7b86ee8a1475896a118"),
  name: "Smartphone XYZ",
  inventory: 100,
  discount: 0.05
}
// After Update
{
  _id: ObjectId("5fd0c7b86ee8a1475896a118"),
  name: "Smartphone XYZ",
  inventory: 95,
  discount: 0.1
}

Before Updates

// Retrieve product information with a specific ID
db.products.findOne({ _id: productId })

This line retrieves a product document from the MongoDB collection products. It seeks a document with exactly the same_id as productId.

Update using $inc and $set

// Update the product with specified changes
db.products.update(
  { _id: productId },
  {
    $inc: { inventory: -5 }, // Decrease inventory by 5 units
    $set: { discount: 0.1 }  // Set a new discount of 10%
  }
)

This block updates a particular product in the products collection. The product is identified by its unique_id. The update operation uses two operators:

• $inc: This operator increments (or in this case, decrements with a negative value) the current value of a field. In this example, it decreases the inventory field by 5 units.
• $set: This operator sets the value of a field. Here, it sets the discount field to 0.1, representing a new discount of 10%.

After Updates

// Retrieve the updated product information
db.products.findOne({ _id: productId })

Following the update, this line retrieves the same product to see the changes. Now, the inventory should be reduced by 5 units, and the discount should reflect the new value of 0.1.

This code is effectively updating a product’s information in MongoDB. It decreases the inventory by 5 units and sets a new discount of 10%, providing a practical example of how to modify data in a MongoDB collection.

Conclusion

MongoDB Updatе Opеrators is еffеctivе data managеmеnt. Thе operators providеs a powerful toolkit for your data to meet evolving requirements. Whether it’s updating fields, arrays, or introducing new elements, MongoDB’s updatе capabilitiеs offеr flexibility and precision.

FAQs on MongoDB Update Operators

How does the $set operator function in MongoDB updates?

The $set operator in MongoDB is used to assign a specific value to a field within a document. It can create new fields if they do not exist and update existing fields with new values.

How does the $addToSet operator differ from $push in MongoDB?

$addToSet adds elements to an array only if they are not already present, ensuring uniqueness. $push, on the other hand, adds elements to the end of an array regardless of their presence.

When should you use the $inc operator in MongoDB?

The $inc operator is ideal for updating numerical fields by incrementing or decrementing their values. It’s commonly used for counters or updating numeric properties like inventory levels.

What is the purpose of the $currentDate operator in MongoDB updates?

The $currentDate operator sets the value of a field to the current date and time. It’s useful for timestamping operations, ensuring that documents reflect their last update time accurately.