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Home Interviews How would you ensure atomicity across multiple object stores in a single transaction? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 06 Jul 2025
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In IndexedDB, you can ensure atomicity across multiple object stores by using a single transaction that spans all the stores you want to access or modify.

What Is Atomicity in IndexedDB?

Atomicity means:

All operations within a transaction either succeed together or fail together — the database is never left in a partial state.

How to Ensure Atomic Operations Across Multiple Stores

Step-by-Step:

const db = await openIndexedDB(); // Assume this opens your DB

const tx = db.transaction(["users", "notes"], "readwrite");

const userStore = tx.objectStore("users");
const noteStore = tx.objectStore("notes");

// Add a user
userStore.put({ id: "u1", name: "Alice" });

// Add a note for that user
noteStore.put({ id: "n1", userId: "u1", content: "My note" });

// Commit is automatic if no error occurs
tx.oncomplete = () => {
    console.log("Transaction committed successfully.");
};

tx.onerror = () => {
    console.error("Transaction failed and was rolled back:", tx.error);
};

If any operation inside the transaction fails, all changes are rolled back automatically.

Key Rules for Atomic Transactions

Rule Explanation
Use the same transaction All operations must be within the same IDBTransaction instance
Use readwrite mode Required if you're writing to the stores
Add all needed stores in one go transaction(["users", "notes"]) — you cannot add stores after
Don’t do async delays inside it IndexedDB transactions auto-close if you yield to the event loop

Pitfall: No await or setTimeout Inside Transactions

const tx = db.transaction(["users", "notes"], "readwrite");

// Don't do this
await fetch("/something");
noteStore.put(...); // Will throw TransactionInactiveError

Transactions auto-close as soon as the JavaScript thread yields.

✅ Instead, prepare all async data before starting the transaction.

Good Pattern with Error Handling

try {
    const tx = db.transaction(["users", "notes"], "readwrite");
    const userStore = tx.objectStore("users");
    const noteStore = tx.objectStore("notes");

    userStore.put({ id: "u1", name: "Alice" });
    noteStore.put({ id: "n1", userId: "u1", content: "Hello!" });

    await new Promise((resolve, reject) => {
        tx.oncomplete = resolve;
        tx.onerror = () => reject(tx.error);
        tx.onabort = () => reject(tx.error);
    });

    console.log("Transaction successful.");
} catch (err) {
    console.error("Transaction failed:", err);
}

Summary

Tip Why it Matters
Use a single transaction([...]) call Ensures atomicity across object stores
Use readwrite mode Required for writes
No async gaps inside transaction Prevents auto-close issues
Use .oncomplete, .onerror, .onabort Detect and respond to success/failure
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