MongoDB $exists

Summary: in this tutorial, you’ll learn how to use the MongoDB $exists operator.

Introduction to the MongoDB $exists operator

The $exists is an element query operator that has the following syntax:

{ field: { $exists: <boolean_value> } }
Code language: CSS (css)

When the <boolean_value> is true, the $exists operator matches the documents that contain the field with any value including null.

If the <boolean_value> is false, the $exists operator matches the documents that don’t contain the field.

The MongoDB $exists doesn’t correspond to the EXISTS operator in SQL.

Notice that MongoDB 4.2 or later doesn’t treat the $type: 0 as the synonym for $exists:false anymore.

MongoDB $exists operator examples

We’ll use the following products collection:

db.products.insertMany([
	{ "_id" : 1, "name" : "xPhone", "price" : 799, "releaseDate" : ISODate("2011-05-14T00:00:00Z"), "spec" : { "ram" : 4, "screen" : 6.5, "cpu" : 2.66 }, "color" : [ "white", "black" ], "storage" : [ 64, 128, 256 ] },
	{ "_id" : 2, "name" : "xTablet", "price" : 899, "releaseDate" : ISODate("2011-09-01T00:00:00Z"), "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("2015-01-14T00:00:00Z"), "spec" : { "ram" : 12, "screen" : 9.7, "cpu" : 3.66 }, "color" : [ "blue" ], "storage" : [ 16, 64, 128 ] },
	{ "_id" : 4, "name" : "SmartPad", "price" : 699, "releaseDate" : ISODate("2020-05-14T00:00:00Z"), "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("2022-09-14T00:00:00Z"), "spec" : { "ram" : 4, "screen" : 9.7, "cpu" : 1.66 }, "color" : [ "white", "orange", "gold", "gray" ], "storage" : [ 128, 256 ] },
	{ "_id" : 6, "name" : "xWidget", "spec" : { "ram" : 64, "screen" : 9.7, "cpu" : 3.66 }, "color" : [ "black" ], "storage" : [ 1024 ] },
	{ "_id" : 7, "name" : "xReader","price": null, "spec" : { "ram" : 64, "screen" : 6.7, "cpu" : 3.66 }, "color" : [ "black", "white" ], "storage" : [ 128 ] }
])
Code language: JavaScript (javascript)

1) Using the MongoDB $exists operator example

The following example uses the $exists operator to select documents where the price field exists:

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

It returned the following documents:

{ "_id" : 1, "name" : "xPhone", "price" : 799 }
{ "_id" : 2, "name" : "xTablet", "price" : 899 }
{ "_id" : 3, "name" : "SmartTablet", "price" : 899 }
{ "_id" : 4, "name" : "SmartPad", "price" : 699 }
{ "_id" : 5, "name" : "SmartPhone", "price" : 599 }
{ "_id" : 7, "name" : "xReader", "price" : null }
Code language: JSON / JSON with Comments (json)

In this example, the $exists operator matches the documents that have the price field including the non-null and null values.

The following query uses the $exists operator that select documents whose price field exists and has a value greater than 799:

db.products.find({
    price: {
        $exists: true,
        $gt: 699
    }
}, {
    name: 1,
    price: 1
});
Code language: CSS (css)

Output:

{ "_id" : 1, "name" : "xPhone", "price" : 799 }
{ "_id" : 2, "name" : "xTablet", "price" : 899 }
{ "_id" : 3, "name" : "SmartTablet", "price" : 899 }
Code language: JSON / JSON with Comments (json)

2) Using the MongoDB $exists operator to query documents that don’t have a specified field

The following example uses the $exists operator to select documents that don’t have the price field:

db.products.find({
    price: {
        $exists: false
    }
}, {
    name: 1,
    price: 1
});
Code language: CSS (css)

It returned one document that doesn’t have the price field:

{ "_id" : 6, "name" : "xWidget" }
Code language: JSON / JSON with Comments (json)

Summary

• Use the { field: {$exists: true} } to select documents that contain the field. It also includes the documents where the field contains null.
• Use the { field: {$exists: false} } to match documents where the field doesn’t exist.