Session and transaction syntax in MongoDB - Step-by-Step Execution

Concept Flow - Session and transaction syntax

Start Session

↓

Begin Transaction

↓

Perform Operations

↓

Commit Transaction?

No→Abort Transaction

↓

End Session

↓

Commit Transaction

↓

End Session

This flow shows starting a session, beginning a transaction, performing operations, then either committing or aborting the transaction, and finally ending the session.

Execution Sample

MongoDB

const session = db.getMongo().startSession();
session.startTransaction();
db.collection.insertOne({item: 'apple'}, {session});
await session.commitTransaction();
session.endSession();

This code starts a session, begins a transaction, inserts a document within the transaction, commits it, and ends the session.

Execution Table

Step	Action	Session State	Transaction State	Operation Result
1	Start session	Active	No transaction	Session started
2	Start transaction	Active	Transaction started	Transaction begun
3	Insert document with session	Active	Transaction started	Document inserted (pending commit)
4	Commit transaction	Active	Transaction committed	Transaction committed successfully
5	End session	Ended	No transaction	Session ended

💡 Session ended after committing the transaction

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
session.state	None	Active	Active	Active	Active	Ended
transaction.state	None	No transaction	Transaction started	Transaction started	Transaction committed	No transaction

Key Moments - 2 Insights

Why does the insert operation need the session parameter?

The insert operation includes the session parameter to ensure it is part of the ongoing transaction, as shown in step 3 of the execution_table.

What happens if commitTransaction is not called?

If commitTransaction is not called, the transaction remains uncommitted and can be aborted, meaning changes won't be saved, as implied by the branch in the concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, what is the transaction state after step 2?

A No transaction

B Transaction committed

C Transaction started

D Transaction aborted

💡 Hint

Refer to the 'Transaction State' column in row for step 2 in execution_table

At which step does the session end?

A Step 5

B Step 4

C Step 3

D Step 2

💡 Hint

Check the 'Session State' column in execution_table for when it changes to 'Ended'

If the transaction is aborted instead of committed, what would be the transaction state after step 4?

A Transaction committed

B Transaction aborted

C Transaction started

D No transaction

💡 Hint

Consider the alternative path in concept_flow where commitTransaction is not called

Concept Snapshot

MongoDB sessions start with startSession().
Use startTransaction() to begin a transaction.
Operations must include the session to be transactional.
Commit with commitTransaction(), or abort with abortTransaction().
End session with endSession().

Full Transcript

This visual execution shows how MongoDB sessions and transactions work step-by-step. First, a session is started, then a transaction begins. Operations like inserts include the session to be part of the transaction. After operations, the transaction is either committed or aborted. Finally, the session ends. Tracking session and transaction states helps understand the flow and ensures data consistency.