In modern web applications, offline support is becoming increasingly important, as users expect to be able to access and manipulate data even without an internet connection. IndexedDB is a powerful client-side database that can store large amounts of data locally in the browser, while PostgreSQL is a popular server-side database that can handle complex data operations efficiently.

To provide seamless data synchronization between IndexedDB and PostgreSQL, we need to establish a reliable and efficient mechanism. In this article, we will explore an approach to achieve data synchronization between these two databases.

Step 1: Data Model Definition

The first step is to define the data models for both IndexedDB and PostgreSQL. These models should match each other to ensure smooth synchronization. You can use an object-relational mapping (ORM) library like Sequelize or TypeORM for PostgreSQL, and the native IndexedDB API for IndexedDB.

Here’s an example of a simple note model defined for both databases:

// Model definition for IndexedDB
class Note {
  constructor(id, title, content) {
    this.id = id;
    this.title = title;
    this.content = content;
  }
}

// Model definition for PostgreSQL (using Sequelize)
const Note = sequelize.define('note', {
  id: {
    type: Sequelize.INTEGER,
    primaryKey: true,
    autoIncrement: true,
  },
  title: Sequelize.STRING,
  content: Sequelize.TEXT,
});

Step 2: Sync Strategy

To synchronize data between IndexedDB and PostgreSQL, we need to determine a synchronization strategy. One popular approach is to use a queue-based system, where changes made in IndexedDB are queued and sent to the server to be applied to the PostgreSQL database.

Queue Data Structure

We can define a simple queue data structure to hold the pending changes:

class SyncQueue {
  constructor() {
    this.queue = [];
  }

  enqueue(change) {
    this.queue.push(change);
  }

  dequeue() {
    return this.queue.shift();
  }

  isEmpty() {
    return this.queue.length === 0;
  }
}

Sync Process

The synchronization process involves two main steps:

1. Push Changes: Whenever a modification is made in IndexedDB, we enqueue the change in the sync queue. The queue can be stored in IndexedDB itself to ensure persistence.

2. Apply Changes: A background process periodically checks the sync queue for pending changes. It dequeues each change, applies it to the PostgreSQL database, and removes it from the queue upon successful synchronization.

Step 3: Implementing Sync Logic

We can now implement the synchronization logic using the strategy defined in Step 2.

Push Changes (IndexedDB to PostgreSQL)

Whenever a change is made to data in IndexedDB (e.g., creating a new note or updating an existing one), we push the change to the sync queue:

function pushChangeToQueue(change) {
  // Enqueue the change in the sync queue (persisted in IndexedDB)
  syncQueue.enqueue(change);
}

Apply Changes (Queue to PostgreSQL)

A background process periodically checks the sync queue for pending changes and applies them to the PostgreSQL database:

function applyChangesFromQueue() {
  while (!syncQueue.isEmpty()) {
    const change = syncQueue.dequeue();

    // Apply the change to the PostgreSQL database
    applyChangeToPostgreSQL(change);
  }
}

Step 4: Handling Offline Mode

In an offline scenario, we need to handle the synchronization process differently. We can use the navigator.onLine property to detect the network status.

Offline Queue

To handle offline mode, we can create a separate offline queue to store pending changes made in IndexedDB:

class OfflineQueue {
  constructor() {
    this.queue = [];
  }

  enqueue(change) {
    this.queue.push(change);
  }

  isEmpty() {
    return this.queue.length === 0;
  }
}

Push Changes (Offline)

Whenever a change is made to data in IndexedDB while offline, we push the change to the offline queue instead of the sync queue:

function pushChangeToOfflineQueue(change) {
  // Enqueue the change in the offline queue (persisted in IndexedDB)
  offlineQueue.enqueue(change);
}

Apply Changes (Queue to PostgreSQL)

When the network connection is restored, we can then apply the pending changes from the offline queue to the PostgreSQL database:

function applyOfflineChanges() {
  if (navigator.onLine) {
    while (!offlineQueue.isEmpty()) {
      const change = offlineQueue.dequeue();

      // Apply the change to the PostgreSQL database
      applyChangeToPostgreSQL(change);
    }
  }
}

Conclusion

Implementing data synchronization between IndexedDB and PostgreSQL allows us to build web applications that provide seamless offline support. By following a synchronization strategy involving queues and background processes, we can ensure that data changes made offline are applied to the server-side database when the connection is restored.

Remember to handle conflicts and design error handling mechanisms to account for any issues that may arise during the synchronization process.

#webdevelopment #databases