How to Use the MongoDB $min Operator to Update Field Values

Summary: in this tutorial, you’ll learn how to use the MongoDB $min operator in the update() method to update the values of one or more fields.

Introduction to the MongoDB $min operator

The $min operator is a field update operator that allows you to update the value of a field to a specified value if the specified value is less than (<) the current value of the field.

The $min operator has the following syntax:

{ $min: {<field1>: <value1>, ...} }

If the current value of a field is greater than or equal to the value that you want to update, the $min operator won’t update the value.

If the field doesn’t exist, the $min operator creates the field and sets its value to the specified value.

MongoDB $min operator example

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]}
 ])

The following example uses the $min operator to update the price of the document _id 5:

db.products.updateOne({
    _id: 5
}, {
    $min: {
        price: 699
    }
})

The query found a matching document. However, it didn’t update any:

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 0 }

The reason is that the new value 699 is greater than the current value 599.

The following example uses the $min operator to update the price of the document _id 5:

db.products.updateOne({
    _id: 5
}, {
    $min: {
        price: 499
    }
})

In this case, the price field of the document _id 5 is updated to 499:

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

This query verifies the update:

db.products.find({
    _id: 5
}, {
    name: 1,
    price: 1
})

Output:

{ "_id" : 5, "name" : "SmartPhone", "price" : 499 }

Summary

• Use the $min operator to update the value of a field to a specified value when the specified value is less than the current field value.