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: JSON / JSON with Comments (json)

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

This 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 quries returns the following documents:

{ "_id" : 1, "name" : "xPhone", "spec" : { "ram" : 4 } } { "_id" : 5, "name" : "SmartPhone", "spec" : { "ram" : 4 } }
Code language: JSON / JSON with Comments (json)

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: JSON / JSON with Comments (json)

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("2020-05-14T00:00:00Z") }
Code language: JSON / JSON with Comments (json)

Summary

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