Array of embedded documents queries in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an embedded document in MongoDB?

An embedded document is a document stored inside another document as a value of a field. It helps group related data together in one place.

beginner

How do you query for documents where an array contains an embedded document with a specific field value?

Use dot notation with the field inside the embedded document. For example, { 'arrayField.fieldName': value } finds documents where the array has an embedded document with that field value.

intermediate

What does the $elemMatch operator do in MongoDB queries?

$elemMatch matches documents where at least one element in an array meets multiple conditions. It helps when you want to match several criteria inside the same embedded document in the array.

intermediate

How can you update a specific embedded document inside an array in MongoDB?

Use the positional operator $ to update the first matching embedded document. For example, db.collection.updateOne({ 'arrayField.field': value }, { $set: { 'arrayField.$.fieldToUpdate': newValue } }) updates the matched embedded document.

intermediate

What is the difference between querying with 'arrayField.field': value and using $elemMatch?

'arrayField.field': value matches if any embedded document in the array has that field value. $elemMatch lets you specify multiple conditions that must all be true in the same embedded document.

Which MongoDB query finds documents where an array contains an embedded document with field 'score' equal to 10?

A { 'array.$.score': 10 }

B { 'array.score': 10 }

C { 'array': 10 }

D { 'array': { $elemMatch: { score: 5 } } }

Using 'array.score': 10 matches documents where any embedded document in 'array' has 'score' equal to 10.

What does the $elemMatch operator allow you to do?

A Remove embedded documents from an array

B Match documents with empty arrays

C Update all embedded documents in an array

D Match multiple conditions inside the same embedded document in an array

$elemMatch matches array elements that satisfy all specified conditions together.

How do you update the first embedded document in an array that matches a condition?

A Use the positional operator $ in the update query

B Use $elemMatch in the update query

C Use $push operator

D Use $unset operator

The positional operator $ identifies the first matching array element to update.

Which query matches documents where an array contains an embedded document with 'score' 10 and 'grade' 'A' in the same element?

A { 'array.score': 10, 'array.grade': 'A' }

B { 'array': { $all: [10, 'A'] } }

C { 'array': { $elemMatch: { score: 10, grade: 'A' } } }

D { 'array.$.score': 10, 'array.$.grade': 'A' }

$elemMatch ensures both conditions apply to the same embedded document.

What is the result of querying { 'array.score': { $gt: 5 } }?

A Documents where any embedded document in 'array' has 'score' greater than 5

B Documents where all embedded documents in 'array' have 'score' greater than 5

C Documents where 'array' contains the number 5

D Documents where 'score' field is greater than 5 outside the array

This query matches if at least one embedded document in 'array' has 'score' > 5.

Explain how to query for documents where an array contains an embedded document matching multiple conditions.

Think about matching several things inside one embedded document in the array.

Describe how to update a specific embedded document inside an array in MongoDB.

Remember the $ operator points to the matched array element.