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The MongoDB Query Language (MQL)

LESSON

Google slide deck available here

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License

(CC BY-NC-SA 3.0)

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Overview

A whole lecture or spread out across multiple lecture periods
Handouts / asynchronous learning
Supplemental reading material - read on your own / not part of formal teaching
Complement to University courses Introduction to MongoDB and MongoDB for SQL Pros

At a Glance

Suggested Uses

Learning Objectives

Length:

70 minutes

Level:

Intermediate

Prerequisites:

Querying in Relational and Non-Relational Databases

At the end of this lesson, learners will be able to:

Describe the use cases for the MongoDB Query Language (MQL).
Perform basic CRUD operations using MQL.
Execute queries using MQL find() and delete().
Use the most common MQL query operators to optimize searches.

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License

(CC BY-NC-SA 3.0)

This lesson is a part of the courses Querying in Non-Relational Databases and Introduction to Modern Databases with MongoDB.

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MongoDB Atlas (cloud)
MongoDB Community (local install)

MongoDB Shell (open source)

This lesson includes exercises

Follow along using these tools

Create a Database

Connect to Your Database

For more instructions on how to use MongoDB Atlas with your students, see Atlas for Educators

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MongoDB Query Language

Simple syntax

Designed to query documents

Only queries a single collection

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MongoDB Query Language

MQL is designed for single collection queries and it is typically used for creating, reading, updating, or deletion (CRUD) operations.

MQL query operators:

Comparison
Logical
Element
Array
Evaluation

Bitwise
Comment
Geospatial
Projection, Update and Update Modifiers

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MQL Find()

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MQL Find()

db.<collection>.find()

Query filter document

db.collection.find({ <field1>: <value1>, ... })

Specifying query operators

db.<collection>.find({ <field1>: { <operator1>: <value1> }, ... })

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MQL Find()

db.<collection>.find()

Query filter document

db.collection.find({ <field1>: <value1>, ... })

Specifying query operators

db.<collection>.find({ <field1>: { <operator1>: <value1> }, ... })

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MQL Find()

db.<collection>.find()

Query filter document

db.collection.find({ <field1>: <value1>, ... })

Specifying query operators

db.<collection>.find({ <field1>: { <operator1>: <value1> }, ... })

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MQL Find(): Important Note

The collection is implicit in MQL based on the query’s criteria.

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Quiz

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Quiz

Which of the following is true for MongoDB MQL find()?

The collection to be queried is part of the query filter document
Query operators can be used to specify conditions in the query filter document
Multiple collections can be queried within a single MQL find()

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Quiz

Which of the following is true for MongoDB MQL find()?

The collection to be queried is part of the query filter document
Query operators can be used to specify conditions in the query filter document
Multiple collections can be queried within a single MQL find()

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Quiz

Which of the following is true for MongoDB MQL find()?

The collection to be queried is part of the query filter document
Query operators can be used to specify conditions in the query filter document
Multiple collections can be queried within a single MQL find()

This is incorrect. The collection is explicitly specified as part of the find syntax, specifically db.collection.find() rather than as part of the query filter document.

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Quiz

Which of the following is true for MongoDB MQL find()?

The collection to be queried is part of the query filter document
Query operators can be used to specify conditions in the query filter document
Multiple collections can be queried within a single MQL find()

This is correct. Query operators can be used to specify conditions within the query filter document.

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Quiz

Which of the following is true for MongoDB MQL find()?

The collection to be queried is part of the query filter document
Query operators can be used to specify conditions in the query filter document
Multiple collections can be queried within a single MQL find()

This incorrect. The syntax of MQL find() limits the query to a single specified collection.

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MQL Query Exercise

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Using MQL Exercise

Let’s use MQL to find people whose age is below 30.

We’ll walk through:

Syntax.
Creating the data and then querying the database to get the results.

We’ll do these via the MongoDB Shell.

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db.people.find(

{

“age”: { $lt: 30 }

}

)

Let’s find the fields in our documents

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db.people.find(

{

“age”: { $lt: 30 }

}

)

With the age field value being $lt (less than) 30

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>>> db.people.insertMany([{ "user_id": "Eoin", "age": 29, "Status": "A"}, { "user_id": "Daniel", "age": 25, "Status": "A", "Country": "USA" }])

…

{

acknowledged : true,

insertedIds : [

ObjectId(5f11c32ae89fad25d8875c1c),

ObjectId(5f11c32ae89fad25d8875c1d)

]

}

Let’s insert some real data on people!

MQL: Exercise

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Let’s find people whose age is below 30

>>> db.people.find({"age":{"$lt":30}})

{ "_id": ObjectId(5f11c32ae89fad25d8875c1c), "user_id" : "Eoin", "age" : 29, "Status" : "A"}

{ "_id": ObjectId(5f11c32ae89fad25d8875c1d), "user_id" : "Daniel", "age" : 25, "Status" : "A", "Country" : "USA" }

MQL: Exercise

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Find the people whose age is great than ($gt) 25.

>>> db.people.find({"age":{"<a>":}})

{ "_id": ObjectId(5f11c32ae89fad25d8875c1c), "user_id" : "Eoin", "age" : 29, "Status" : "A"}

Using the same window, change <a> to the operator for greater than.

Change to the value necessary to find all people whose age is greater than 25.

MQL: Exercise

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Create Read Update Delete (CRUD)

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MQL Create

insertOne(): Insert one document into a collection.

insertMany(): Insert an array of documents into a collection.

writeConcern: Sets the level of acknowledgment requested from MongoDB for write operations.

ordered: For insertMany() �there is an additional option �for controlling whether the documents are inserted in ordered or unordered fashion.

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>> db.cows.insertOne({name: "daisy", milk: 8}, {writeConcern: {w: "majority"}})

{

"acknowledged" : true,

"insertedId" : ObjectId("5f4e0c5b2d4b45b7f11b6d50")

}

>>> db.cows.insertMany([{name: "buttercup", milk: 9}, {name: "rose", milk: 7}], {writeConcern: {w: "majority"}, ordered: false})

{

"acknowledged" : true,

"insertedIds" : [

ObjectId("5f4e0ce52d4b45b7f11b6d51"),

ObjectId("5f4e0ce52d4b45b7f11b6d52")

]

}

Example: MQL Create

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MQL Read

find(): Selects documents and returns cursor.

findOne(): Returns first document that satisfies criteria.

findAndModify(): Modifies and returns a single document.

findOneAndDelete(): Deletes & returns the deleted document.

findOneAndUpdate(): Updates a single document.

findOneAndReplace(): Replaces a single document.

We have already covered the R/Read with the find() function, however there are several other find functions that are also worth flagging here.

find(): returns a cursor to the results for the query document. The query document holds the criteria you want to filter the documents on and the projection document further refines the criteria by selecting specific fields to be returned.

findAndModify(): finds and then updates atomically a single document.

findOne() finds and returns a single document.

findOneAndXXX(): includes findOneAndDelete(), findOneAndUpdate(), findOneAndReplace(). These perform the related action again on a single document returning the original document (whether deleted, updated, or replaced). In the case of findOneAndUpdate() and findOneAndReplace() you can specify returnNewDocument: true to return the updated document or the replaced document (the new document).

findOneAndUpdate() and findOneAndReplace() perform a read and an atomic write.

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>>> db.cows.findAndModify({query: {name: "daisy", milk: 8}, update: { $set: {milk: 12} }})

{

"_id" : ObjectId("5f4e0c5b2d4b45b7f11b6d50"),

"name" : "daisy",

"milk" : 8

}

Example: MQL Read

>> db.cows.find({name: "daisy", milk: 8})

{ "_id" : ObjectId("5f4e0c5b2d4b45b7f11b6d50"), "name" : "daisy", "milk" : 8 }

>>> db.cows.find({name: "daisy", milk: 12})

{ "_id" : ObjectId("5f4e0c5b2d4b45b7f11b6d50"), "name" : "daisy", "milk" : 12 }

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MQL Update

updateOne(): Update one document into a collection

updateMany(): Update an array of documents into a collection.

Update in similar fashion to Create has two functions, updateOne and updateMany, which operate on a single document and on an array of documents respectively.

Both functions take a filter document which specifies which documents to be updated. If the filter document is empty the first document in the collection is updated. These functions also take a second document as an argument which contains the various options that can be configured.

The default behaviour is not to insert a new document if the update cannot find a suitable document or documents that match the filter document. It is possible using the upsert: True parameter in the second document supplied to the function (the options document) to set that if a document isn’t found that a new one will be inserted (hence the term upsert - update and insert).

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>>> db.cows.find({})

{ "_id" : ObjectId("5f4e0c5b2d4b45b7f11b6d50"), "name" : "daisy", "milk" : 9 }

{ "_id" : ObjectId("5f4e0ce52d4b45b7f11b6d51"), "name" : "buttercup", "milk" : 10 }

{ "_id" : ObjectId("5f4e0ce52d4b45b7f11b6d52"), "name" : "rose", "milk" : 8 }

Example: MQL Update

>>> db.cows.updateOne({name: "daisy", milk: 12},{ $set: {milk: 8} })

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }

>>> db.cows.updateMany({}, {$inc: {milk: 1}})

{ "acknowledged" : true, "matchedCount" : 3, "modifiedCount" : 3 }

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MQL Delete

deleteOne(): Deletes one document from a collection.

deleteMany(): Deletes many documents from a collection.

writeConcern: Sets the level of acknowledgment requested from MongoDB for write operations.

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>>> db.cows.deleteOne({milk: 9})

{ "acknowledged" : true, "deletedCount" : 1 }

>>> db.cows.deleteMany({}, {writeConcern: {w: "majority"}})

{ "acknowledged" : true, "deletedCount" : 2 }

Example: MQL Delete

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MQL: xxxMany ( )

Create: insertMany()

Update: updateMany()

Delete: deleteMany()

The Many variants apply to multiple records, however, insertMany() takes an Array of documents.

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CRUD: MQL Exercise

>>> cowCol = db.getCollection("cow")

Test.cow

>>> cowCol.drop()

>>> for(c=0;c<10;c++) {

cowCol.insertOne({ name: "daisy", milk: c} )

}

{

acknowledged : true,

insertedIds : ObjectId(5f2aefa8fde88235b959f0b1e),

}

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>>> cowCol.findAndModify(({ query: { milk: { $gt: <A> } }, sort: { milk: 1 }, update: { $set: { : true } } }))

{ "_id" : ObjectId("5f4e50da2d4b45b7f11b6d76"), "name" : "daisy", "milk" : 6, "expected_milk" : 5 }

>> cowCol.find({"sell" : true})

{ "_id" : ObjectId("5f4e50da2d4b45b7f11b6d76"), "name" : "daisy", "milk" : 6, "expected_milk" : 5, "sell": true }

Using the shell window, change <A> to update the first document with the milk field value of 6 as the document we want to update.

Change to the highlighted field name shown in the find() query below.

CRUD: MQL Exercise

In this exercise we will use findAndModify ( ) to update a document.

In the same window, you should replace <A> to update the first document with the milk field value of 6 as the document we want to update

You should change to the field which represents milk in the document.

The result should be similar (the ObjectIds will differ) will firstly be the original document as findAndModify needs the option new: true to return the updated document rather than the original document.

The second find output is the updated document and it has the additional field “sell” that we used the $set operator in the findAndModify query to update the document to add the field with a value of true.

cowCol.findAndModify({ query: { milk: { $gt: 5 } }, sort: { milk: 1 }, update: { $set: { sell: true } } })

cowCol.find({"sell" : true})

See: https://docs.mongodb.com/manual/reference/method/db.collection.findAndModify/

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>>> cowCol.updateMany({ milk: { <A>: 5 } }, { : { sell: true } })

{ "acknowledged" : true, "matchedCount" : 4, "modifiedCount" : 3 }

Using the shell window again, change <A> to the greater than operator

Change to the operator we will use to set the value of the field in the documents we will update.

As we already updated one of the eligible documents, only 3 are modified.

CRUD: MQL Exercise

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Quiz

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Quiz

Which of the following are true for MongoDB MQL?

All the CRUD functions in MQL take a filter document
findAndModify() is an atomic operation
findOneAndUpdate() and findOneAndReplace() perform a read and an atomic write
find() is the only CRUD function which returns a cursor

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Quiz

Which of the following are true for MongoDB MQL?

All the CRUD functions in MQL take a filter document
findAndModify() is an atomic operation
findOneAndUpdate() and findOneAndReplace() perform a read and an atomic write
find() is the only CRUD function which returns a cursor

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Quiz

Which of the following are true for MongoDB MQL?

All the CRUD functions in MQL take a filter document
findAndModify() is an atomic operation
findOneAndUpdate() and findOneAndReplace() perform a read and an atomic write
find() is the only CRUD function which returns a cursor

This incorrect. The insertOne and insertMany functions do not take a filter document.

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Quiz

Which of the following are true for MongoDB MQL?

All the CRUD functions in MQL take a filter document
findAndModify() is an atomic operation
findOneAndUpdate() and findOneAndReplace() perform a read and an atomic write
find() is the only CRUD function which returns a cursor

This is correct. The findAndModify function is atomic in terms of the modifications to the single document it operates upon.

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Quiz

Which of the following are true for MongoDB MQL?

All the CRUD functions in MQL take a filter document
findAndModify() is an atomic operation
findOneAndUpdate() and findOneAndReplace() perform a read and an atomic write
find() is the only CRUD function which returns a cursor

This is correct. This is how these functions operate, firstly the read and then the atomic write.

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Quiz

Which of the following are true for MongoDB MQL?

All the CRUD functions in MQL take a filter document
findAndModify() is an atomic operation
findOneAndUpdate() and findOneAndReplace() perform a read and an atomic write
find() is the only CRUD function which returns a cursor

This is correct. All the other functions return a document rather than a cursor.

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MQL Delete

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MQL Delete

Specifically the db.collection.deleteOne() and db.collection.deleteMany() methods but also db.collection.drop().

To delete all documents from a collection, pass an empty filter document {} to the db.collection.deleteMany() method

Additional methods include db.collection.findOneAndDelete() and db.collection.findAndModify(), both offer a sort option. Deletes are also possible via the db.collection.bulkWrite() method.

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MQL Delete

Specifically the db.collection.deleteOne() and db.collection.deleteMany() methods but also db.collection.drop().

To delete all documents from a collection, pass an empty filter document {} to the db.collection.deleteMany() method

Additional methods include db.collection.findOneAndDelete() and db.collection.findAndModify(), both offer a sort option. Deletes are also possible via the db.collection.bulkWrite() method.

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MQL Delete

Specifically the db.collection.deleteOne() and db.collection.deleteMany() methods but also db.collection.drop().

To delete all documents from a collection, pass an empty filter document {} to the db.collection.deleteMany() method

Additional methods include db.collection.findOneAndDelete() and db.collection.findAndModify(), both offer a sort option. Deletes are also possible via the db.collection.bulkWrite() method.

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Quiz

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Quiz

Which of the following are true for MongoDB MQL?

A non-empty filter document must be given for the deleteXXX() methods
Deletes cannot be sorted
Deletes are atomic operations

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Quiz

Which of the following are true for MongoDB MQL?

A non-empty filter document must be given for the deleteXXX() methods
Deletes cannot be sorted
Deletes are atomic operations

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Quiz

Which of the following are true for MongoDB MQL?

A non-empty filter document must be given for the deleteXXX() methods
Deletes cannot be sorted
Deletes are atomic operations

This incorrect. Using {} or an empty document will delete all documents in the collection.

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Quiz

Which of the following are true for MongoDB MQL?

A non-empty filter document must be given for the deleteXXX() methods
Deletes cannot be sorted
Deletes are atomic operations

This incorrect. It is possible with db.collection.findOneAndDelete() or with db.collection.findAndModify(), both offer the ability to sort order of the documents for deletion.

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Quiz

Which of the following are true for MongoDB MQL?

A non-empty filter document must be given for the deleteXXX() methods
Deletes cannot be sorted
Deletes are atomic operations

This is correct. All write operations in MongoDB are atomic, a delete is a write operation.

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MQL Query Operators: Comparison

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MQL Query Operators

Comparison

Logical

Element, Array, Evaluation, Bitwise, Comment, Geospatial, and Projection

Update and Update Modifiers

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MQL Query Operators: Comparison

$lt Exists and less than

$lte: Exists and less than or equal to

$gt: Exists and greater than

$gte: Exists and greater than or equal to

$ne: Does not exist or does but not equal to

$eq: Exists and equal to

$in: Exists and in a set

$nin: Does not exist or not in a set

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>>> cowCol = db.getCollection("cow")

test.cow

>>> for(c=0;c<10;c++) {

cowCol.insertOne({ name: "daisy", milk: c} )

}

{

"acknowledged" : true,

"insertedId" : ObjectId("5f2aefa8fde88235b959f0b1e")

}

>>> cowCol.find({milk:{$gt:6}})

{"_id": ObjectId("5f2aefa8fde88235b959f0b1c"), "name": "daisy", milk: 7}

{"_id": ObjectId("5f2aefa8fde88235b959f0b1d"), "name": "daisy", milk: 8}

{"_id": ObjectId("5f2aefa8fde88235b959f0b1e"), "name": "daisy", milk: 9}

MQL Operators Comparison: Example

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MQL Operator Comparison: Exercise

>>> cowCol = db.getCollection("cow")

test.cow

>>> for(c=0;c<10;c++) {

cowCol.insertOne({ name: "daisy", milk: c} )

}

{

acknowledged : true,

insertedIds : ObjectId(5f2aefa8fde88235b959f0b1e),

}

Let’s insert some real data on cows!

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MQL Operator Comparison: Exercise

Find the docs with the field “milk” greater than 6.

>>> cowCol.find({milk:{$gt:6}})

{ "_id": ObjectId(5f2aefa8fde88235b959f0b1c), "name" : "daisy", "milk" : 7 }

{ "_id": ObjectId(5f2aefa8fde88235b959f0b1d), "name" : "daisy", "milk" : 8 }

{ "_id": ObjectId(5f2aefa8fde88235b959f0b1e), "name" : "daisy", "milk" : 9 }

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MQL Operator Comparison: Exercise

Using updateMany ( ) to update 3 documents. Using the same window, change <a> to the operator for less than or equal. Change to the value necessary to find all the documents whose milk is less than or equal to 3.

>>> cowCol.find({milk:{<a>:}})

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d67"), "name" : "daisy", "milk" : 0 }

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d67"), "name" : "daisy", "milk" : 1 }

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d67"), "name" : "daisy", "milk" : 2 }

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d67"), "name" : "daisy", "milk" : 3 }

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MQL Query Operators Cont.

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MQL Query Operators

Comparison

Logical

Element, Array, Evaluation, Bitwise, Comment, Geospatial, and Projection

Update and Update Modifiers

Diverse Search Parameters

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MQL Query Operators: Logical

$or Match either of two or more values

$not Used with other operators to negate

$nor Match neither of two or more values

$and Match both of two or �more values

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>>> cowCol.find({$and: [ {milk: { $gt: 6 } }, {milk: { $lt: 9 } } ] })

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d6e"), "name": "daisy", "milk": 7 }

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d6f"), "name": "daisy", "milk": 8 }

Logical Operator: Example One

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>>> cowCol.find({milk:{$not:{$gt:6}}})

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d67"), "name": "daisy", "milk": 0 }

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d68"), "name": "daisy", "milk": 1 }

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d69"), "name": "daisy", "milk": 2 }

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d6a"), "name": "daisy", "milk": 3 }

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d6b"), "name": "daisy", "milk": 4 }

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d6c"), "name": "daisy", "milk": 5 }

{"_id": ObjectId("5f4e41d12d4b45b7f11b6d6d"), "name": "daisy", "milk": 6 }

Logical Operator: Example Two

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MQL Query Operators

Comparison

Logical

Element, Array, Evaluation, Bitwise, Comment, Geospatial, and Projection

Update and Update Modifiers

Diverse Search Parameters

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MQL Query Operators: Various categories

$exists: Match documents that have the specific field

$type: Selects documents if a field is of the specified type

$elemMatch: Selects documents if element �in the array field matches all the specified $elemMatch conditions. Limits the contents �of an <array> field from the query results �to contain only the first element matching �the conditions.

$comment: Adds a comment to a query predicate

$expr: Allows use of aggregation expressions within the query language

$geoWithin: Selects geometries within a bounding GeoJSON geometry, requires either a 2dsphere or a 2d index

$: Selects and returns first match in array that meets condition

$slice: Limits the number of elements projected from an array

Here’s a subset of the specific operators available from the Element, Array, Evaluation, Bitwise, Comment, Geospatial, and Projection categories. The documentation site for MongoDB contains the full list along with any caveats for their usage.

$exists is a useful operator that ensures a specific field exists, $type selects documents based on whether or not the field is of a specific type, $elemMatch selects documents if an element in the array field matches it’s specified conditions, $comment is another useful operator as you can add a comment to your query which is logged in the profile log.

Looking at the set of expressions start at the top with $expr which provides the ability to use aggregation expressions within MQL queries. There are several geospatial operators but we’ll just look at $geoWithin which allows for queries bound by a GeoJSON geometry. The $ operator returns the first match in an array that satisfies the condition. Lastly, $slice limits the number of elements that are projected from an array for the results.

These operators span a wide set of functionality. A useful operator is the $comment which sends the comment to the profile log when the MQL statement is executed. This can be helpful when debugging or tracing the performance of your queries.

$expr can built help build more complex aggregation expressions within MQL.

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MQL Query Operators: $expr

$expr Example comparing two fields in the same collection

In this example, we again use cows and milk, however we add the ‘expected_milk’ field. This field is set one above or below the ‘milk’ field, above if ‘milk’ is an odd number or below if ‘milk’ is even.

>>>cowCol = db.getCollection("cow")

Test.cow

>>> cowCol.drop()

>>> for(c=1;c<10;c++) {

a = 0

if(c%2==0) {

a = c-1

} else {

a = c+1

}

cowCol.insertOne({ name: "daisy", milk: c, expected_milk: a} )

}

>>> cowCol.find( { $expr: { $gt: [ "$milk" , "$expected_milk" ] } } ).count()

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Here’s the full result for our previous example…

>>> cowCol.find({ $expr: { $gt: [ "$milk" , "$expected_milk" ] } } )

{ "_id": ObjectId(5f351f10dcb672556f30f5fa), "name" : "daisy", "milk" : 2, "expected_milk" : 1 }

{ "_id": ObjectId(5f351f10dcb672556f30f5fc), "name" : "daisy", "milk" : 4, "expected_milk" : 3 }

{ "_id": ObjectId(5f351f10dcb672556f30f5fe), "name" : "daisy", "milk" : 6, "expected_milk" : 5 }

{ "_id": ObjectId(5f351f10dcb672556f30f600), "name" : "daisy", "milk" : 8, "expected_milk" : 7 }

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MQL Query Operators

Comparison

Logical

Element, Array, Evaluation, Bitwise, Comment, Geospatial, and Projection

Update and Update Modifiers

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MQL Query Operators: Various Categories

$inc: Increments the specific field by the specified amount

$currentDate: Sets the field to the current date, either as a Date or as a Timestamp

$set: Sets the value of the field to the specified value

$setOnInsert: Similar to $set but only performs this when there is an insert of a new document, it won’t update existing documents if present

$rename: Changes a field’s name to the specified name

$max: Only updates the field if the value specified is greater than the existing value

$addToSet: Selects and returns first match in array that meets condition

$push: Adds an item to an array

$each: Modifies the $push and $addToSet operators to append multiple items for array updates

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Query Operators: Exercise

>>> for(c=0;c<10;c++) {cowCol.insertOne({ name: "daisy", milk: c})

}

{

acknowledged : true,

insertedIds : ObjectId(5f2aefa8fde88235b959f0b1e),

}

>>> cowCol = db.getCollection("cow")

Test.cow

>>> cowCol.drop()

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Find the docs where milk is greater than 8

>>> cowCol.find({milk:{$gt:8}})

{ "_id": ObjectId(5f2aefa8fde88235b959f0b1e), "name" : "daisy", "milk" : 9 }

>>> cowCol.find({milk:{$gt:8}})

{ "_id": ObjectId(5f2aefa8fde88235b959f0b1e), "name" : "rose", "milk" : 9 }

>>> cowCol.update({ milk: 9 }, { $set: { "name" : "rose" }, $setOnInsert: { milk: 10 }}, { upsert: true } );

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Using updateMany() to update 3 documents

>>> cowCol.find({milk:{<a>:}})

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d67"), "name" : "daisy", "milk" : 0 }

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d68"), "name" : "daisy", "milk" : 1 }

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d69"), "name" : "daisy", "milk" : 2 }

{ "_id" : ObjectId("5f4e41d12d4b45b7f11b6d6a"), "name" : "daisy", "milk" : 3 }

Using the same window, change <a> to the operator for less than or equal to.

Change to the value necessary to find all the documents whose milk is less than or equal to 3.

75 of 86

Quiz

76 of 86

Quiz

Which of the following are true for MongoDB MQL?

$in and $nin both use sets to determine membership or not
$gt and $gte will both check of documents with fields exceeding or greater than the specified criteria
$eq and $ne check the value is equal or not equal to the specified criteria

77 of 86

Quiz

Which of the following are true for MongoDB MQL?

$in and $nin both use sets to determine membership or not
$gt and $gte will both check of documents with fields exceeding or greater than the specified criteria
$eq and $ne check the value is equal or not equal to the specified criteria

78 of 86

Quiz

Which of the following are true for MongoDB MQL?

$in and $nin both use sets to determine membership or not
$gt and $gte will both check of documents with fields exceeding or greater than the specified criteria
$eq and $ne check the value is equal or not equal to the specified criteria

This is correct. Both the $in and the $nin functions in MQL use a set to determine the membership or not for a particular piece of data.

79 of 86

Quiz

Which of the following are true for MongoDB MQL?

$in and $nin both use sets to determine membership or not
$gt and $gte will both check of documents with fields exceeding or greater than the specified criteria
$eq and $ne check the value is equal or not equal to the specified criteria

This is correct. The logic checks in both the $gt and the $gte will verify whether fields exceed (are greater than) the specified criteria.

80 of 86

Quiz

Which of the following are true for MongoDB MQL?

$in and $nin both use sets to determine membership or not
$gt and $gte will both check of documents with fields exceeding or greater than the specified criteria
$eq and $ne check the value is equal or not equal to the specified criteria

This incorrect. Both $eq and $ne further check for the exists or not of the specified criteria.

81 of 86

Quiz

Which of the following are true for MongoDB MQL?

$and works with multiple (more than two) operators.
$and works with multiple (more than two) fields.
$or can be nested.
$set will not create new fields when you specify multiple field-value pairs.

82 of 86

Quiz

Which of the following are true for MongoDB MQL?

$and works with multiple (more than two) operators.
$and works with multiple (more than two) fields.
$or can be nested.
$set will not create new fields when you specify multiple field-value.

This is correct. The $and operator allows you to use two or more operators together.

83 of 86

Quiz

Which of the following are true for MongoDB MQL?

$and works with multiple (more than two) operators.
$and works with multiple (more than two) fields.
$or can be nested.
$set will not create new fields when you specify multiple field-value pairs.

This is correct. The $and operator allows you to work with multiple fields in a MQL query.

84 of 86

Quiz

Which of the following are true for MongoDB MQL?

$and works with multiple (more than two) operators.
$and works with multiple (more than two) fields.
$or can be nested.
$set will not create new fields when you specify multiple field-value pairs.

This is correct. It can be nested to provide more complex logical conditions.

85 of 86

Quiz

Which of the following are true for MongoDB MQL?

$and works with multiple (more than two) operators.
$and works with multiple (more than two) fields.
$or can be nested.
$set will not create new fields when you specify multiple field-value pairs.

This incorrect. $set will create new fields in single or multiple field-value pairs if they do not already exist.

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