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My Personal MongoDB Guide
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MongoBD-Guide-7.0.md

Startup and Shutdown

In the terminal type mongosh to start cli client

$ mongosh

This will give the following output:

Current Mongosh Log ID: 66b5d45f5650b1dc223f83cc
Connecting to:          mongodb://127.0.0.1:27017/?directConnection=true&serverSelectionTimeoutMS=2000&appName=mongosh+1.3.1
Using MongoDB:          7.0.12
Using Mongosh:          1.3.1

For mongosh info see: https://docs.mongodb.com/mongodb-shell/

------
   The server generated these startup warnings when booting:
   2024-08-09T12:29:26.815+05:30: Access control is not enabled for the database. Read and write access to data and configuration is unrestricted
------

Type cls to clear the terminal.

Type exit to exit mongosh.

Databases

show dbs Statement

To display all databases, enter show dbs

test> show dbs
admin     41 kB
config  73.7 kB
local   73.7 kB

use Statement

Type use <database-name> to select a particular database. If the database does not exist, it is created.

For example, use admin will select the admin database.

test> use admin
switched to db admin

Typing use school will create a new database school which will then be selected.

test> use students
switched to db students

Currently the show dbs command will not show the school database as it does not contain any data.

Note

Any newly created database will not be listed in show dbs, as it's empty. To change this, collections will have to be added to it.

Database Drop/Deletion

db.dropDatabase() will delete the selected database.

For example with the school database selected,

db.dropDatabase() will drop the school database.

school> db.dropDatabase()
{ ok: 1, dropped: 'school' }

{ ok: 1, dropped: 'school' } means deletion is successful.

To go back to the previous state, type

school> use school
db.createCollection("students")

Creating Collections

Type db.createCollection("<collection-name>") to create a new collection.

For example with the school database selected, typing db.createCollection("students") will create a new collection students.

school> db.createCollection("students")
{ ok: 1 }

{ ok: 1 } means collection creation is successful.

Now show dbs will display the school database.

Display Collections

show collections will display all collections within the selected database:

school> show collections
students

GeeksForGeeks
MongoDB Docs

Rename Collection

To rename any collecection simply enter:

db.originalCollectionName.renameCollection('newCollectionName')

GeeksForGeeks
MongoDB Docs

Delete Collection

db.collection.drop()

GeeksForGeeks
MongoDB Docs

Inserting Objects

school> db.students.insertOne({name: "Spongebob", age: 30, gpa: 3.2})
{
  acknowledged: true,
  insertedId: ObjectId("66afc2c13aaa44348d3380e4")
}

Find

db.students.find() will display all objects.

school> db.students.find().limit(1)
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  }
]

Insert Many

The insertMany() function can import many objects at once. Just make an Array containing all the elements and pass it to the function

school> db.students.insertMany([{name:"Patrick", age:38, gpa:1.5}, {name:"Sandy", age:27, gpa:4.0}, {name: "Gary", age:18, gpa:2.5}])`

A successful insertion will give the following message:

{
  acknowledged: true,
  insertedIds: {
    '0': ObjectId("66afd3763aaa44348d3380e5"),
    '1': ObjectId("66afd3763aaa44348d3380e6"),
    '2': ObjectId("66afd3763aaa44348d3380e7")
  }
}

Now db.students.find() will give:

school> db.students.find()
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5
  }
]

Data Types

There are many supported data types including Strings, Boolean, Date, null, Array, Object and various other types for numbers. For the more info, click here

school> db.students.insertOne({
  name:"Larry", 
  age: 32,
  gpa: 2.8,
  fullTime: false,
  registerDate: new Date(),
  graduationDate: null,
  courses: ["Biology", "Chemistry", "Calculus"],
  address: { street:"123 Fake St.",
             city: "Bikini Bottom",
             zip: 12345
           }
})

The Date() constructor by default, will return the current date and time. But you can make a Date instance with specific Date and Time by passing it as a string:

Date("2023-01-02T00:00:00");

Upon successful insertion:

{
  acknowledged: true,
  insertedId: ObjectId("66afe0293aaa44348d3380e8")
}

Sort

Sorting students in ascending order by name:

school> db.students.find().sort({name:1})

Sorting students in descending order by name:

school> db.students.find().sort({name:-1})

Sorting students in ascending order by gpa:

school> db.students.find().sort({gpa:1})

Sorting students in descending order by gpa:

school> db.students.find().sort({gpa:-1})

Limit

The limit() function can limit the number of documents/objects returned

Th below statement, returns only one document

school> db.students.find().limit(1)
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  }
]

By default, objects in a collection are sorted by their ObjectID values in ascending order

The first elements in this sequence is objects is returned, when using limit()

To return three documents:

school> db.students.find().limit(3)
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  }
]

To find student with the highest GPA:

school> db.students.find().sort({gpa:-1}).limit(1)
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  }
]

Find with Query & Projection

You can use the find method to search for documents that match a specified query. It's parameters are as follows:

db.collectionName.find({query}, {projection})

Query Parameter

To find objects where the fields match specified values:

db.collectionName.find({fieldKey: "fieldValue"})

For example, to find all entries where name is assigned "Spongebob":

school> db.students.find({name: "Spongebob"})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2
  }
]

To find all entries where gpa is assigned 4.0:

school> db.students.find({gpa: 4.0})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4
  }
]

To find all entries where fullTime is assigned false:

school> db.students.find({fullTime: false})
[
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

To find all entries where fullTime is assigned true:

school> db.students.find({gpa:40, fullTime:true})

The above query does not return anything, since it does not match any entries.

Projection Parameter

To return only the specified fields:

db.collectionName.find({}, {requiredFieldKey: true})

OR

db.collectionName.find({}, {requiredFieldKey: 1})

To display only the name fields of students:

db.students.find({}, {name: true})

OR

db.students.find({}, {name: 1})

Example:

school> db.students.find({}, {name: true})
[
  { _id: ObjectId("66afc2c13aaa44348d3380e4"), name: 'Spongebob' },
  { _id: ObjectId("66afd3763aaa44348d3380e5"), name: 'Patrick' },
  { _id: ObjectId("66afd3763aaa44348d3380e6"), name: 'Sandy' },
  { _id: ObjectId("66afd3763aaa44348d3380e7"), name: 'Gary' },
  { _id: ObjectId("66afe0293aaa44348d3380e8"), name: 'Larry' }
]

This would return the _id and name fields. Although it's not specified, the _id key and values are also returned by default.

To exclude a given field:

db.collectionName.find({}, {excludedFieldKey: false})

For example, to return only the name key and exclude the _id key:

school> db.students.find({}, {_id:false, name: true})
[
  { name: 'Spongebob' },
  { name: 'Patrick' },
  { name: 'Sandy' },
  { name: 'Gary' },
  { name: 'Larry' }
]

To return the name and gpa keys and exclude the _id key:

school> db.students.find({}, {_id:false, name:true, gpa:true})
[
  { name: 'Spongebob', gpa: 3.2 },
  { name: 'Patrick', gpa: 1.5 },
  { name: 'Sandy', gpa: 4 },
  { name: 'Gary', gpa: 2.5 },
  { name: 'Larry', gpa: 2.8 }
]

Update One

db.students.updateOne(filter, update)

Set operator

school> db.students.updateOne({name:"Spongebob"},{$set:{fullTime:true}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}
school> db.students.find({name:"Spongebob"})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: true
  }
]
school> db.students.updateOne({_id: ObjectId("66afc2c13aaa44348d3380e4")}, {$set:{fullTime:false}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}
school> db.students.find({_id: ObjectId("66afc2c13aaa44348d3380e4")})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  }
]

Unset Operator

Removes fields

school> db.students.updateOne({_id: ObjectId("66afc2c13aaa44348d3380e4")}, {$unset:{fullTime:""}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}
school> db.students.find({_id: ObjectId("66afc2c13aaa44348d3380e4")})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2
  }

Update Many

All entries will have fullTime added with valure false

school> db.students.updateMany({}, {$set:{fullTime:false}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 5,
  modifiedCount: 4,
  upsertedCount: 0
}
school> db.students.find()
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Unset Again

Removes the fullTime property whare the name filed has a value of Gary

db.students.updateOne({name:"Gary"}, {$unset:{fullTime:""}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}
school> db.students.find({name:"Gary"})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5
  }
]

Removes the fullTime property where the name field has a value of Sandy

school> db.students.updateOne({name:"Sandy"}, {$unset:{fullTime:""}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}
school> db.students.find({name:"Sandy"})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4
  }
]

Both Sandy and Gary have their fullTime fields removed.

school> db.students.find()
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Exists operator

Selects all entries which do not have the fullTime property.

Adds the fulTime proerties to those entries.

Sets those vales of FullTime in those entries to true.

db.students.updateMany({fullTime:{$exists:false}}, {$set:{fullTime:true}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 2,
  modifiedCount: 2,
  upsertedCount: 0
}

Gary and Sandy now have fullTime set to true

school> db.students.find()
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Delete One

db.students.deleteOne({name:"Larry"})
{ acknowledged: true, deletedCount: 1 }
school> db.students.find({name:"Larry"})

school>
school> db.students.find()
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  }
]

Delete Many

db.students.deleteMany({fullTime:false})
{ acknowledged: true, deletedCount: 2 }
school> db.students.find()
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  }
]

Delete Many with Exists operator

school> db.students.deleteMany({registerDate:{$exists:false}})
{ acknowledged: true, deletedCount: 2 }
school> db.students.find()

school>

Comparison operators

Not Equals Operator

Reinsert all elements with

db.students.insertMany([{_id:ObjectId("66afc2c13aaa44348d3380e4"),name:'Spongebob',age:30,gpa:3.2,fullTime:false},{_id:ObjectId("66afd3763aaa44348d3380e5"),name:'Patrick',age:38,gpa:1.5,fullTime:false},{_id:ObjectId("66afd3763aaa44348d3380e6"),name:'Sandy',age:27,gpa:4,fullTime:true},{_id:ObjectId("66afd3763aaa44348d3380e7"),name:'Gary',age:18,gpa:2.5,fullTime:true},{_id:ObjectId("66afe0293aaa44348d3380e8"),name:'Larry',age:32,gpa:2.8,fullTime:false,registerDate:ISODate("2024-08-04T20:10:17.770Z"),graduationDate:null,courses:['Biology','Chemistry','Calculus'],address:{street:'123FakeSt.',city:'BikiniBottom',zip:12345}}])

Returns all entries except entries where name is Spongebob

school> db.students.find({name:{$ne:"Spongebob"}})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Less Than Operator

school> db.students.find({age:{$lt:20}})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  }
]

Less Than Equal To Operator

school> db.students.find({age:{$lte:27}})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  }
]

Greater Than Operator

school> db.students.find({age:{$gt:27}})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Greater Than Equal To Operator

school> db.students.find({age:{$gte:27}})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Combined Operations

school> db.students.find({gpa:{$gte:3, $lte:4}})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  }
]

In Operator

For multiple matches, will return all matching elements.

school> db.students.find({name:{$in:["Spongebob", "Patrick", "Sandy"]}})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  }
]

Not In Operator

Opposite of in Operator. Returns non matching items.

school> db.students.find({name:{$nin:["Spongebob", "Patrick", "Sandy"]}})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Logical Operators

And Operator

school> db.students.find({$and: [{fullTime:true}, {age: {$lte: 22}}]})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  }
]

Or Operator

school> db.students.find({$or: [{fullTime:true}, {age: {$lte: 22}}]})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  }
]

NOR Operation

school> db.students.find({$nor: [{fullTime:true}, {age: {$lte: 22}}]})
[
  {
    _id: ObjectId("66afc2c13aaa44348d3380e4"),
    name: 'Spongebob',
    age: 30,
    gpa: 3.2,
    fullTime: false
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e5"),
    name: 'Patrick',
    age: 38,
    gpa: 1.5,
    fullTime: false
  },
  {
    _id: ObjectId("66afe0293aaa44348d3380e8"),
    name: 'Larry',
    age: 32,
    gpa: 2.8,
    fullTime: false,
    registerDate: ISODate("2024-08-04T20:10:17.770Z"),
    graduationDate: null,
    courses: [ 'Biology', 'Chemistry', 'Calculus' ],
    address: { street: '123 Fake St.', city: 'Bikini Bottom', zip: 12345 }
  }
]

Lets make some alternations

db.students.find({age:{$lt:30}})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: 18,
    gpa: 2.5,
    fullTime: true
  }
]

Setting Gary's age to null

school> db.students.updateOne({name:"Gary"}, {$set:{age:null}})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}

Now

school> db.students.find({age:{$lt:30}})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  }
]

NOT Operator

Ruturns all entries where age is not greater than or equal to 30

school> db.students.find({age:{$not:{$gte:30}}})
[
  {
    _id: ObjectId("66afd3763aaa44348d3380e6"),
    name: 'Sandy',
    age: 27,
    gpa: 4,
    fullTime: true
  },
  {
    _id: ObjectId("66afd3763aaa44348d3380e7"),
    name: 'Gary',
    age: null,
    gpa: 2.5,
    fullTime: true
  }
]

Sources:

https://www.mongodb.com/docs/mongodb-shell/

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