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Why Identify Users?

When users interact with your app anonymously, you see disconnected events. When you identify users, those events connect into a journey: Anonymous tracking: 
Event: button_clicked
Event: page_viewed
Event: purchase_made
Identified tracking: 
User user_123:
  → button_clicked
  → page_viewed
  → purchase_made
Now you can answer questions like “What do users do before they purchase?” or “How many times did this user visit?”

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Setting User ID

Set the user ID once, and all future events include it: 
// When user logs in
grain.setUserId('user_123');

// All these events now belong to user_123
grain.track('dashboard_viewed');
grain.track('report_generated');
grain.track('settings_updated');
When to set user ID:
  • Right after user logs in
  • When app loads (if user already authenticated)
  • After successful signup

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The identify() Method

identify() is an alias for setUserId() - they do the same thing: 
// These are equivalent
grain.identify('user_123');
grain.setUserId('user_123');
Use whichever reads better in your code. Many analytics tools use identify(), so we support both for familiarity.

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Getting Current User ID

Check which user is currently identified: 
const userId = grain.getUserId();

if (userId) {
  console.log(`Tracking as user: ${userId}`);
} else {
  console.log('Anonymous tracking');
}
This is useful for conditionally showing features or debugging.

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User ID in Initialization

You can set the user ID when creating the client: 
const grain = createGrainAnalytics({
  tenantId: 'your-tenant-id',
  userId: 'user_123'
});

// Events immediately track with this user ID
grain.track('app_opened');
This is convenient when you know the user ID upfront, like in server-side code or after authentication.

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Clearing User ID

When users log out, clear the user ID to stop associating events with them: 
// User logs out
grain.setUserId(null);

// Events are now anonymous
grain.track('logged_out');
Always clear user IDs on logout! Otherwise, the next user’s events will be attributed to the previous user.

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Persistent vs Session-Based

The SDK doesn’t persist user IDs automatically. When the page reloads, you need to set it again: 
// On app load, restore user from your auth system
const currentUser = getCurrentUser(); // Your auth logic

if (currentUser) {
  grain.setUserId(currentUser.id);
}
Why not persist automatically? User sessions are managed by your authentication system (Auth0, Firebase, etc.). Grain follows your lead instead of duplicating session logic.

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Best Practices

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Use Stable IDs

Use IDs that don’t change, like database IDs or UUIDs: 
// ✅ Good: Stable user ID
grain.setUserId('user_8f3a2c1b');

// ❌ Bad: Email might change
grain.setUserId('user@example.com');

// ❌ Bad: Session ID changes every session
grain.setUserId('session_xyz123');

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Set Early

Identify users as early as possible to capture all their events: 
// React example
function App() {
  const { user } = useAuth();

  useEffect(() => {
    if (user) {
      grain.setUserId(user.id);
    } else {
      grain.setUserId(null);
    }
  }, [user]);

  // ... rest of app
}

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Don’t Switch Frequently

Avoid switching between many different user IDs from the same client. This can trigger rate limiting. Learn more in Security.

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User Properties

After identifying users, you can add properties to their profile. This is covered in detail in User Properties. 
// Identify user
grain.setUserId('user_123');

// Add properties
await grain.setProperty({
  plan: 'premium',
  signup_date: '2024-01-15'
});

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Anonymous to Identified

You can track users anonymously first, then identify them later: 
// Anonymous tracking
grain.track('landing_page_viewed');
grain.track('signup_button_clicked');

// User signs up - now identify them
grain.setUserId('user_123');

// Identified tracking
grain.track('account_created');
Events before identification remain anonymous. Only events after setUserId() are associated with the user.

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Server-Side Identification

In backend code, set the user ID for each request: 
// API route handler
app.post('/api/action', async (req, res) => {
  const userId = req.user.id;
  
  grain.setUserId(userId);
  await grain.track('api_action_performed', {
    endpoint: '/api/action'
  }, { flush: true });
  
  // ... handle request
});
In serverless environments, create a new Grain instance per request to avoid mixing user IDs: 
// Serverless function
export async function handler(event) {
  const grain = createGrainAnalytics({
    tenantId: 'your-tenant-id',
    userId: event.userId
  });

  await grain.track('function_executed', {}, { flush: true });
  
  return { statusCode: 200 };
}

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React Integration

When using React hooks, user identification happens automatically through the provider: 
import { GrainProvider } from '@grainql/analytics-web/react';

function App() {
  const { user } = useAuth();

  return (
    <GrainProvider 
      config={{ 
        tenantId: 'your-tenant-id',
        userId: user?.id  // Updates automatically when user changes
      }}
    >
      <YourApp />
    </GrainProvider>
  );
}
Learn more in React Integration.

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Next Steps

User Properties

Add attributes to user profiles

Security

Understand user ID security