DevTinder Project - API Development: Feed API and Pagination

Code Demonstration Link

• DevTinder Backend Repository Project

Overview

Today's focus is on enhancing the Get /user/feed API by implementing pagination. The API is designed to retrieve user profiles while filtering out specific users and limiting the number of results per request.

API Details

Endpoint:

• GET /user/feed

Purpose:

• Fetch profiles of other users while excluding:
  • The logged-in user.
  • Existing connections.
  • Ignored users.
  • Users who have already received a connection request.

Thought Process for API Development

1. Filtering Out Unwanted Users

• Use a Set data structure to collect and store the following user IDs:

  • fromUserId and toUserId from all connection requests associated with the logged-in user.
  • This prevents duplicate filtering and ensures an optimized query.

• Use MongoDB operators:

  • $nin: Exclude multiple user IDs in a single query.
  • $ne: Ensure the logged-in user's profile is not included in the query results.

2. Implementing Pagination

• Why Pagination?

  • If there are 1000+ users, returning all users at once would be inefficient.
  • Pagination ensures that only a specific number of users are retrieved per request.

• Fetching page and limit from Request Parameters:

  • page: Determines which page of users the client is requesting.
  • limit: Defines the maximum number of users to be returned.

• Calculating the Skip Value:

  • The formula for calculating skipped records:
    Copy

    skip = (page - 1) * limit
    

  • skip: Number of users to ignore before returning results.

• Applying Skip and Limit in the Query:

  • skip() is used to move past the number of users from previous pages.
  • limit() ensures only the requested number of users is retrieved.

Key Concepts

1. Set-Based Filtering for Efficient Querying

• Using a Set prevents duplicates and ensures only valid user IDs are excluded from the query.
• This helps in maintaining fast query performance.

2. MongoDB Query Optimization

• $nin: Excludes all users in the filter list.
• $ne: Ensures the logged-in user's profile does not appear in the results.

3. Pagination for Better Performance

• Pagination prevents excessive data loading, reducing server response time.
• Allows for smooth user experience with "Load More" or infinite scrolling features.

   userRouter.get("/user/feed", userAuth, async (req, res) => {
  try {
    const loggedInUser = req.user;

    const page = parseInt(req.query.page || 1);
    let limit = parseInt(req.query.limit || 10);
    limit = limit > 50 ? 50 : limit;
    const skip = (page - 1) * limit;

    const connectionRequest = await ConnectionRequestModel.find({
      $or: [{ fromUserId: loggedInUser._id }, { toUserId: loggedInUser._id }],
    }).select("fromUserId toUserId");

    const hideUsersFromFeed = new Set();
    connectionRequest.forEach((req) => {
      hideUsersFromFeed.add(req.fromUserId.toString());
      hideUsersFromFeed.add(req.toUserId.toString());
    });

    const users = await User.find({
      $and: [
        { _id: { $nin: Array.from(hideUsersFromFeed) } },
        { _id: { $ne: loggedInUser._id } },
      ],
    })
      .select(USER_SAFE_DATA)
      .skip(skip)
      .limit(limit);

    res.send(users);
  } catch (error) {
    res.status(400).send("ERROR: " + error.message);
  }
});
module.exports = userRouter;

Benefits of This Approach

1. Improved Performance:

   • Querying a subset of users per request optimizes response times.

2. Scalability:

   • Ensures that the API remains efficient even with a large number of users.

3. Better User Experience:

   • Users receive paginated data, making the browsing experience smooth.

Conclusion

The Get /user/feed API now supports pagination, ensuring that user profiles are efficiently retrieved while maintaining a smooth and scalable user experience. Filtering with MongoDB queries and pagination techniques enhances the performance and usability of the DevTinder app.