Machine Learning & Big Data Blog

23 Common MongoDB Operators & How To Use Them

8 minute read
Shanika Wickramasinghe
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In this article, we will take a look at the most commonly used query operators. We’ll explain what they do, then share examples so you can see how they work.

(This article is part of our MongoDB Guide. Use the right-hand menu to navigate.)

What are MongoDB operators?

MongoDB offers different types of operators that can be used to interact with the database. Operators are special symbols or keywords that inform a compiler or an interpreter to carry out mathematical or logical operations.

The query operators enhance the functionality of MongoDB by allowing developers to create complex queries to interact with data sets that match their applications.

MongoDB offers the following query operator types:

  • Comparison
  • Logical
  • Element
  • Evaluation
  • Geospatial
  • Array
  • Bitwise
  • Comments

MongoDB operators can be used with any supported MongoDB command.

Now, let’s look at commonly used operators. (We won’t touch on them all, there are so many.) We’ll use the following dataset with the find() function to demonstrate each operator’s functionality.

  • Database: supermarket
  • Collections: employees, inventory, payments, promo
use supermarket
db.employees.find()
db.inventory.find()
db.payments.find()
db.promo.find()

Dataset:

Comparison Operators

MongoDB comparison operators can be used to compare values in a document. The following table contains the common comparison operators.

Operator Description
$eq Matches values that are equal to the given value.
$gt Matches if values are greater than the given value.
$lt Matches if values are less than the given value.
$gte Matches if values are greater or equal to the given value.
$lte Matches if values are less or equal to the given value.
$in Matches any of the values in an array.
$ne Matches values that are not equal to the given value.
$nin Matches none of the values specified in an array.

$eq Operator

In this example, we retrieve the document with the exact _id value “LS0009100”.

db.inventory.find({"_id": { $eq: "LS0009100"}}).pretty()

Result:

$gt and $lt Operators

In this example, we retrieve the documents where the `quantity` is greater than 5000.

db.inventory.find({"quantity": { $gt: 5000}}).pretty()

Result:

Let’s find the documents with the ‘quantity’ less than 5000.

db.inventory.find({"quantity": { $lt: 5000}}).pretty()

Result:

$gte and $lte Operators

Find documents with ‘quantity’ greater than or equal to 5000.

db.inventory.find({"quantity": { $gte: 12000}}).pretty()

Result:

The following query returns documents where the quantity is less than or equal to 1000.

db.inventory.find({"quantity": { $lte: 1000}}).pretty()

Result:

$in and $nin Operators

The following query returns documents where the price field contains the given values.

db.inventory.find({"price": { $in: [3, 6]}}).pretty()

Result:

If you want to find documents where the price fields do not contain the given values, use the following query.

db.inventory.find({"price": { $nin: [5.23, 3, 6, 3.59, 4.95]}}).pretty()

Result:

$ne Operator

Find documents where the value of the price field is not equal to 5.23 in the inventory collection.

db.inventory.find({"price": { $ne: 5.23}})

Result:

Logical Operators

MongoDB logical operators can be used to filter data based on given conditions. These operators provide a way to combine multiple conditions. Each operator equates the given condition to a true or false value.

Here are the MongoDB logical operators:

Operator Description
$and Joins two or more queries with a logical AND and returns the documents that match all the conditions.
$or Join two or more queries with a logical OR and return the documents that match either query.
$nor The opposite of the OR operator. The logical NOR operator will join two or more queries and return documents that do not match the given query conditions.
$not Returns the documents that do not match the given query expression.

$and Operator

Find documents that match both the following conditions

  • job_role is equal to “Store Associate”
  • emp_age is between 20 and 30
db.employees.find({ $and: [{"job_role": "Store Associate"}, {"emp_age": {$gte: 20, $lte: 30}}]}).pretty()

Result:

$or and $nor Operators

Find documents that match either of the following conditions.

  • job_role is equal to “Senior Cashier” or “Store Manager”
db.employees.find({ $or: [{"job_role": "Senior Cashier"}, {"job_role": "Store Manager"}]}).pretty()

Result:

Find documents that do not match either of the following conditions.

  • job_role is equal to “Senior Cashier” or “Store Manager”
db.employees.find({ $nor: [{"job_role": "Senior Cashier"}, {"job_role": "Store Manager"}]}).pretty()

Result:

$not Operator

Find documents where they do not match the given condition.

  • emp_age is not greater than or equal to 40
db.employees.find({ "emp_age": { $not: { $gte: 40}}})

Result:

Element Operators

The element query operators are used to identify documents using the fields of the document. The table given below lists the current element operators.

Operator Description
$exists Matches documents that have the specified field.
$type Matches documents according to the specified field type. These field types are specified BSON types and can be defined either by type number or alias.

$exists Operator

Find documents where the job_role field exists and equal to “Cashier”.

db.employees.find({ "emp_age": { $exists: true, $gte: 30}}).pretty()

Result:

Find documents with an address field. (As the current dataset does not contain an address field, the output will be null.)

db.employees.find({ "address": { $exists: true}}).pretty()

Result:

$type Operator

The following query returns documents if the emp_age field is a double type. If we specify a different data type, no documents will be returned even though the field exists as it does not correspond to the correct field type.

db.employees.find({ "emp_age": { $type: "double"}})

Result:

db.employees.find({ "emp_age": { $type: "bool"}})

Result:

Evaluation Operators

The MongoDB evaluation operators can evaluate the overall data structure or individual field in a document. We are only looking at the basic functionality of these operators as each of these operators can be considered an advanced MongoDB functionality. Here is a list of common evaluation operators in MongoDB.

Operator Description
$jsonSchema Validate the document according to the given JSON schema.
$mod Matches documents where a given field’s value is equal to the remainder after being divided by a specified value.
$regex Select documents that match the given regular expression.
$text Perform a text search on the indicated field. The search can only be performed if the field is indexed with a text index.
$where Matches documents that satisfy a JavaScript expression.

$jsonSchema Operator

Find documents that match the following JSON schema in the promo collection.

The $let aggregation is used to bind the variables to a results object for simpler output. In the JSON schema, we have specified the minimum value for the “period” field as 7, which will filter out any document with a lesser value.

let promoschema = {
bsonType: "object",
required: [ "name", "period", "daily_sales" ],
properties: {
"name": {
bsonType: "string",
description: "promotion name"
},
"period": {
bsonType: "double",
description: "promotion period",
minimum: 7,
maximum: 30
},
"daily_sales": {
bsonType: "array"
}
}
}
db.promo.find({ $jsonSchema: promoschema }).pretty()

Result:

$mod Operator

Find documents where the remainder is 1000 when divided by 3000 in the inventory collection.

Note that the document “Milk Non-Fat – 1lt” is included in the output because the quantity is 1000, which cannot be divided by 3000, and the remainder is 1000.

db.inventory.find({"quantity": {$mod: [3000, 1000]}}).pretty()

Result:

$regex Operator

Find documents that contain the word “Packed” in the name field in the inventory collection.

db.inventory.find({"name": {$regex: '.Packed.'}}).pretty()

Result:

$text Operator

Find documents by using a text searching for “Non-Fat” in the name field. If the field is not indexed, you must create a text index before searching.

db.inventory.createIndex({ "name": "text"})

Result:

db.inventory.find({ $text: { $search: "Non-Fat"}}).pretty()

Result:

$where Operator

Find documents from the “payments” collection where the _id field is a string type and equals the given md5 hash defined as a JavaScript function.

db.payments.find({ $where: function() { var value =  isString(this._id) && hex_md5(this._id) == '57fee1331906c3a8f0fa583d37ebbea9'; return value; }}).pretty()

Result:

Array Operators

MongoDB array operators are designed to query documents with arrays. Here are the array operators provided by MongoDB.

Operator Description
$all Matches arrays that contain all the specified values in the query condition.
$size Matches the documents if the array size is equal to the specified size in a query.
$elemMatch Matches documents that match specified $elemMatch conditions within each array element.

$all Operator

Find documents where the category array field contains “healthy” and “organic” values.

db.inventory.find({ "category": { $all: ["healthy", "organic"]}}).pretty()

Result:

$size Operator

Find documents where the category array field has two elements.

db.inventory.find({ "category": { $size: 2}}).pretty()

Result:

$elemMatch Operator

Find documents where at least a single element in the “daily_sales” array is less than 200 and greater than 100.

db.promo.find({ "daily_sales": { $elemMatch: {$gt: 100, $lt: 200}}}).pretty()

Result:

Comment Operator

The MongoDB comment query operator associates a comment to any expression taking a query predicate. Adding comments to queries enables database administrators to trace and interpret MongoDB logs using the comments easily.

$comment Operator

Find documents where the period is equal to 7 in promo collection while adding a comment to the find operation.

db.promo.find({ "period": { $eq: 7}, $comment: "Find Weeklong Promos"}).pretty()

Result:

Adding comments lets users easily identify commands in MongoDB logs. The above operation will be logged as follows.

db.adminCommand( { getLog:'global'} ).log.forEach(x => {print(x)})

Result:

Conclusion

In this article, we have only scratched the surface of MongoDB operators. We can further extend the overall functionality of the database using projection and aggregations.

Related reading

Free E-book: The Beginner’s Guide to MongoDB

MongoDB is the most popular NoSQL database today and with good reason. This e-book is a general overview of MongoDB, providing a basic understanding of the database.


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About the author

Shanika Wickramasinghe

Shanika Wickramasinghe is a software engineer by profession and a graduate in Information Technology. Her specialties are Web and Mobile Development. Shanika considers writing the best medium to learn and share her knowledge. She is passionate about everything she does, loves to travel, and enjoys nature whenever she takes a break from her busy work schedule. You can connect with her on LinkedIn.