Specify a Query

Overview

Most CRUD operations allow you to narrow the set of matched documents by specifying matching criteria in a query document. Query documents contain one or more query operators that apply to specific fields which determine which documents to include in the result set.

In a query document, you can match fields against literal values, such as { title: 'The Room' }, or you can compose query operators to express more complex matching criteria. In this guide, we cover the following categories of query operators in MongoDB and show examples on how to use them:

• Comparison Operators

• Logical Operators

• Element Operators

• Evaluation Operators

To follow along with the examples in this guide, use the following code snippet to insert documents that describe fruits into the myDB.fruits collection:

const myDB = client.db("myDB");
const myColl = myDB.collection("fruits");
await myColl.insertMany([
  { "_id": 1, "name": "apples", "qty": 5, "rating": 3 },
  { "_id": 2, "name": "bananas", "qty": 7, "rating": 1, "microsieverts": 0.1 },
  { "_id": 3, "name": "oranges", "qty": 6, "rating": 2 },
  { "_id": 4, "name": "avocados", "qty": 3, "rating": 5 },
]);

Literal Value Queries

Literal value queries allow you to query for data that exactly matches a value you provide in the query document. A literal value query has two parts: a field name and a value. Documents returned from such a query must contain a field that has exactly the same name as the provided name and a value for that field that is exactly the same as the provided value. The following operation uses a literal query to search for documents containing a field called "name" that has a value of "apples":

const query = { "name": "apples" };
const cursor = myColl.find(query);
for await (const doc of cursor) {
  console.dir(doc);
}

This code snippet returns the following results:

{ "_id": 1, "name": "apples", "qty": 5, "rating": 3 }

myColl.find({
   rating: { $eq: 5 }
});

myColl.find({
   rating: 5
});

Comparison Operators

Comparison operators allow you to query for data based on comparisons with values in a collection. Common comparison operators include $gt for "greater than" comparisons, $lt for "less than" comparisons, and $ne for "not equal to" comparisons. The following operation uses the comparison operator $gt to search for documents with a quantity value greater than 5 and prints them out:

// $gt means "greater than"
const query = { qty: { $gt : 5 } };
const cursor = myColl.find(query);
for await (const doc of cursor) {
  console.dir(doc);
}

This code snippet returns the following results:

{ "_id": 2, "name": "bananas", "qty": 7, "rating": 1 }
{ "_id": 3, "name": "oranges", "qty": 6, "rating": 2 }

Logical Operators

Logical operators allow you to query for data using logic applied to the results of field-level operators. For instance, you can use the $or method to query for documents that match either a $gt comparison operator or a literal value query. The following operation uses the logical operator $not to search for documents with a quantity value that is not greater than 5 and prints them out:

const query = { qty: { $not: { $gt: 5 }}};
const cursor = myColl.find(query);
for await (const doc of cursor) {
  console.dir(doc);
}

This code snippet returns the following results:

{ "_id": 4, "name": "avocados", "qty": 3, "rating": 5 }
{ "_id": 1, "name": "apples", "qty": 5, "rating": 3 }

myColl.find({
  rating: { $eq: 5 },
  qty: { $gt: 4 }
});

myColl.find({
  $and: [
     { rating: { $eq: 5 }},
     { qty: { $gt: 4 }}
  ]
});

For more information on comparison operators, see the reference manual entry for Comparison Query Operators.

Element Operators

Element operators allow you to query based on the presence, absence, or type of a field. The following operation uses the element operator $exists to search for documents containing the microsieverts field:

const query = { microsieverts: { $exists: true } };
const cursor = myColl.find(query);
for await (const doc of cursor) {
  console.dir(doc);
}

This code snippet returns the following results:

{ "_id": 2, "name": "bananas", "qty": 7, "rating": 1, "microsieverts": 0.1 }

For more information on this operator, see the reference manual entry for the $exists operator.

Evaluation Operators

Evaluation operators allow you to execute higher level logic, like regex and text searches, when querying for documents in a collection. Common evaluation operators include $regex and $text. The following operation uses the evaluation operator $mod to search for documents with a quantity value that is divisible by 3 with a remainder of 0:

// $mod means "modulo" and returns the remainder after division
const query = { qty: { $mod: [ 3, 0 ] } };
const cursor = myColl.find(query);
for await (const doc of cursor) {
  console.dir(doc);
}

This code snippet returns the following results:

{ "_id": 3, "name": "oranges", "qty": 6, "rating": 2 }
{ "_id": 4, "name": "avocados", "qty": 3, "rating": 5 }

For more information on this operator, see the reference manual entry for the $mod operator.