Summary: in this tutorial, you’ll learn how to use the MongoDB $mul
operator to multiply the value of a field by a number.
Introduction to MongoDB $mul operator
The $mul
is a field update operator that allows you to multiply the value of a field by a specified number.
The $mul
operator has the following syntax:
{ $mul: { <field1>: <number1>, <field2>: <number2>, ... } }
The <field>
that you want to update must contain a numeric value. To specify a field in an embedded document or in an array, you use the dot notation e.g., <embedded_doc>.<field>
or <array>.<index>
.
If the field doesn’t exist in the document, the $mul
operator creates the field and sets its value to zero.
MongoDB $mul operator examples
We’ll use the following products
collection:
db.products.insertMany([
{ "_id" : 1, "name" : "xPhone", "price" : 799, "releaseDate": ISODate("2011-05-14"), "spec" : { "ram" : 4, "screen" : 6.5, "cpu" : 2.66 },"color":["white","black"],"storage":[64,128,256]},
{ "_id" : 2, "name" : "xTablet", "price" : 899, "releaseDate": ISODate("2011-09-01") , "spec" : { "ram" : 16, "screen" : 9.5, "cpu" : 3.66 },"color":["white","black","purple"],"storage":[128,256,512]},
{ "_id" : 3, "name" : "SmartTablet", "price" : 899, "releaseDate": ISODate("2015-01-14"), "spec" : { "ram" : 12, "screen" : 9.7, "cpu" : 3.66 },"color":["blue"],"storage":[16,64,128]},
{ "_id" : 4, "name" : "SmartPad", "price" : 699, "releaseDate": ISODate("2020-05-14"),"spec" : { "ram" : 8, "screen" : 9.7, "cpu" : 1.66 },"color":["white","orange","gold","gray"],"storage":[128,256,1024]},
{ "_id" : 5, "name" : "SmartPhone", "price" : 599,"releaseDate": ISODate("2022-09-14"), "spec" : { "ram" : 4, "screen" : 5.7, "cpu" : 1.66 },"color":["white","orange","gold","gray"],"storage":[128,256]}
])
1) Using the MongoDB $mul to multiply the value of a field
The following example uses the $mul
operator to multiply the price of the document _id 5
by 10%
:
db.products.updateOne({
_id: 5
},
{
$mul: {
price: 1.1
}
})
The output document showed that the query matched one document and updated it:
{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }
The following query verifies the update:
db.products.find({
_id: 5
}, {
name: 1,
price: 1
})
Output:
{ "_id" : 5, "name" : "SmartPhone", "price" : 658.9000000000001 }
2) Using the MongoDB $mul to multiply the values of array elements
The following query uses the $mul
operator to double the values of the first, second, and third array elements in the storage
array of the document _id 1
:
db.products.updateOne({
_id: 1
}, {
$mul: {
"storage.0": 2,
"storage.1": 2,
"storage.2": 2
}
})
Output:
{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }
The following query uses the findOne()
method to select the document with _id 1
to verify the update:
db.products.findOne({
_id: 1
}, {
name: 1,
storage: 1
})
Output:
{ "_id" : 1, "name" : "xPhone", "storage" : [ 128, 256, 512 ] }
3) Using the $mul operator to multiply the values of a field in embedded documents
This example uses the $mul
operator to double the values of the ram
field in the spec
embedded documents of all documents from the products
collection:
db.products.updateMany({}, {
$mul: {
"spec.ram": 2
}
})
Output:
{ "acknowledged" : true, "matchedCount" : 5, "modifiedCount" : 5 }
The following query returns all documents from the products
collection:
db.products.find({}, {
name: 1,
"spec.ram": 1
})
Output:
{ "_id" : 1, "name" : "xPhone", "spec" : { "ram" : 8 } }
{ "_id" : 2, "name" : "xTablet", "spec" : { "ram" : 32 } }
{ "_id" : 3, "name" : "SmartTablet", "spec" : { "ram" : 24 } }
{ "_id" : 4, "name" : "SmartPad", "spec" : { "ram" : 16 } }
{ "_id" : 5, "name" : "SmartPhone", "spec" : { "ram" : 8 } }
Summary
- Use the MongoDB
$mul
operator to multiply the value of a field by a specified number.