MongoDB Shell (mongosh) basics - Step-by-Step Execution

Concept Flow - MongoDB Shell (mongosh) basics

Start mongosh

↓

Connect to MongoDB

↓

Show databases

↓

Select database

↓

Show collections

↓

Run queries or commands

↓

Exit mongosh

This flow shows how you start the MongoDB shell, connect to the server, explore databases and collections, run commands, and then exit.

Execution Sample

MongoDB

mongosh
show dbs
db = db.getSiblingDB('testdb')
db.createCollection('users')
db.users.insertOne({name: 'Alice'})
db.users.find()

This code starts the shell, lists databases, switches to 'testdb', creates a collection, inserts a document, and finds documents.

Execution Table

Step	Command	Action	Result
1	mongosh	Start MongoDB shell	Connected to MongoDB server
2	show dbs	List all databases	[admin, local, testdb]
3	db = db.getSiblingDB('testdb')	Switch to 'testdb' database	Switched to 'testdb'
4	db.createCollection('users')	Create 'users' collection	Collection 'users' created
5	db.users.insertOne({name: 'Alice'})	Insert document into 'users'	Inserted 1 document with _id
6	db.users.find()	Find all documents in 'users'	[{_id: ObjectId(...), name: 'Alice'}]
7	exit	Exit mongosh	Shell closed

💡 User exits the shell with 'exit' command

Variable Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	After Step 6	Final
db	default	testdb	testdb	testdb	testdb	testdb
users collection	none	none	created	created with 1 document	created with 1 document	created with 1 document

Key Moments - 3 Insights

Why do we use db.getSiblingDB('testdb') instead of just db?

Because 'db' starts as the default database (usually 'test'), getSiblingDB switches to the named database without restarting the shell. See execution_table step 3.

What does insertOne return and why is _id important?

insertOne returns an object with the inserted document's _id, which uniquely identifies the document. This is shown in execution_table step 5.

Why does find() return an array with ObjectId?

Because find() returns documents matching the query; each document has a unique _id of type ObjectId. See execution_table step 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'db' after step 3?

A 'testdb'

B 'admin'

C 'local'

D 'default'

💡 Hint

Check the variable_tracker table under 'db' after Step 3

At which step is the 'users' collection created?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Action' column in execution_table for collection creation

If you run db.users.find() before inserting any documents, what would the result be?

A A document with _id

B An error

C An empty array []

D The collection is deleted

💡 Hint

Think about what find() returns when no documents exist in the collection

Concept Snapshot

MongoDB Shell (mongosh) basics:
- Start shell with 'mongosh'
- Use 'show dbs' to list databases
- Switch DB with db.getSiblingDB('name')
- Create collections with createCollection()
- Insert documents with insertOne()
- Query documents with find()
- Exit shell with 'exit'

Full Transcript

This lesson shows how to use the MongoDB shell called mongosh. First, you start the shell by typing 'mongosh'. Then, you can list all databases using 'show dbs'. To work with a specific database, use db.getSiblingDB('databaseName'). You can create a collection with createCollection('collectionName'). To add data, use insertOne() with a document. To see data, use find(). Finally, exit the shell by typing 'exit'. Each step changes the state of the shell and database, which we tracked in the tables.