MongoDB $eq

Summary: in this tutorial, you’ll learn how to use the MongoDB $eq operator to specify an equality condition.

Introduction to the MongoDB $eq operator

The $eq operator is a comparison query operator that allows you to match documents where the value of a field equals a specified value.

The following shows the syntax of $eq operator:

{ <field>: { $eq: <value> } }
Code language: HTML, XML (xml)

The query is equivalent to the following:

{<field>: <value>}
Code language: HTML, XML (xml)

MongoDB $eq operator examples

We’ll use the following products collection for the demonstration:

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" : 9.7, "cpu" : 1.66 },"color":["white","orange","gold","gray"],"storage":[128,256]}
 ])
Code language: JavaScript (javascript)

1) Using $eq operator to check if a field equals a specified value

The following example uses the $eq operator to query the products collection to select all documents where the value of the price field equals 899:

db.products.find({
    price: {
        $eq: 899
    }
}, {
    name: 1,
    price: 1
})
Code language: CSS (css)

The query is equivalent to the following:

db.products.find({
    price: 899
}, {
    name: 1,
    price: 1
})
Code language: CSS (css)

They both match the following documents:

[
  { _id: 2, name: 'xTablet', price: 899 },
  { _id: 3, name: 'SmartTablet', price: 899 }
]
Code language: JavaScript (javascript)

2) Using the $eq operator to check if a field in an embedded document equals a value

The following example uses the $eq operator to search for documents where the value of the ram field in the spec document equals 4:

db.products.find({
    "spec.ram": {
        $eq: 4
    }
}, {
    name: 1,
    "spec.ram": 1
})
Code language: PHP (php)

It is equivalent to the following:

db.products.find({
    "spec.ram": 4

}, {
    name: 1,
    "spec.ram": 1
})
Code language: JavaScript (javascript)

Both of these queries returns the following documents:

[
  { _id: 1, name: 'xPhone', spec: { ram: 4 } },
  { _id: 5, name: 'SmartPhone', spec: { ram: 4 } }
]
Code language: JavaScript (javascript)

3) Using $eq operator to check if an array element equals a value

The following example uses the $eq operator to query the products collection to find all documents where the array color contains an element with the value "black":

db.products.find({
    color: {
        $eq: "black"
    }
}, {
    name: 1,
    color: 1
})
Code language: CSS (css)

It’s equivalent to:

db.products.find({
    color: "black"

}, {
    name: 1,
    color: 1
})
Code language: CSS (css)

Both queries return the following matching documents:

[
  { _id: 1, name: 'xPhone', color: [ 'white', 'black' ] },
  { _id: 2, name: 'xTablet', color: [ 'white', 'black', 'purple' ] }
]
Code language: JavaScript (javascript)

4) Using $eq operator to check if a field equals a date

The following example uses the $eq operator to select documents in the widget collection with the published date is 2020-05-14:

db.products.find({
    releaseDate: {
        $eq: new ISODate("2020-05-14")
    }
}, {
    name: 1,
    releaseDate: 1
})
Code language: CSS (css)

It returned the following document:

[
  {
    _id: 4,
    name: 'SmartPad',
    releaseDate: ISODate("2020-05-14T00:00:00.000Z")
  }
]
Code language: JavaScript (javascript)

Summary

• Use the $eq operator to specify an equality condition.