Understanding Parse.com and the Issue at Hand

Introduction to Parse.com

Parse.com is a cloud-based backend-as-a-service (BaaS) platform designed for mobile app developers. It provides a scalable infrastructure for handling tasks such as user authentication, data storage, and API calls. In this article, we’ll explore how Parse.com handles updates on segues and the potential pitfalls that can lead to inconsistent behavior.

Background on Segues

In iOS development, a segue is an instance of the UIStoryboardSegue class used to transition between two view controllers. When a segue is triggered, it involves several steps:

1. Segue preparation: The view controller prepares for the segue by updating its properties and any additional data required.
2. Segue execution: Once prepared, the segue is executed, allowing the transition between view controllers to occur.
3. Post-segue processing: After the segue has completed, the target view controller may need to update its properties based on the results of the previous view controller.

The Issue at Hand

The question presents a scenario where only one property (gotpromoCode) is updated correctly during the segue, while others (promoCode and senderUserId) remain unchanged. This inconsistency occurs even when the code for updating these properties is called before the segue. Understanding why this happens requires an in-depth look into how Parse.com handles updates on segues.

How Parse.com Handles Updates

When using Parse.com with your iOS app, data is stored in a cloud-based database and updated via API calls. When you update user properties using PFUser.currentUser()!.setValue(), it triggers the following sequence of events:

1. Cloud synchronization: The changes are sent to the cloud for storage.
2. Database updates: Parse.com’s server processes the update request, storing it in its database.

Understanding the Problem

To understand why some properties are updated while others are not, we need to examine how segues interact with Parse.com’s cloud-based database:

1. Cloud caching: When you access a property from PFUser.currentUser(), the value is retrieved from the local cache stored on your device.
2. Server-side updates: During the segue, the setValue() method sends an update request to Parse.com’s server. This triggers the cloud synchronization and database updates process.

The Root Cause of Inconsistency

The inconsistency arises because the order in which properties are updated can affect the outcome:

1. gotpromoCode and senderUserId: These properties are updated after their respective API calls have completed.
2. promoCode: This property is updated immediately, triggering a sync request to Parse.com’s server.

Solution Overview

To resolve this inconsistency, we need to ensure that all relevant updates occur synchronously, preventing any potential issues with data consistency:

1. Synchronous updates: By saving the results after setting the values using saveInBackground(), we can guarantee that any subsequent updates occur in a consistent manner.
2. Preventing premature updates: To avoid premature updates, we need to ensure that all necessary updates have completed before proceeding with further actions.

Solution Implementation

Let’s examine how we can implement these solutions:

1. Synchronous Updates

PFUser.currentUser()!.setValue(object.objectId!, forKey: “senderUserId”) PFUser.currentUser()!.saveInBackground()

    By adding `saveInBackground()` to the end of each update statement, we ensure that all changes are synchronized before continuing with other operations.

2.  **Preventing Premature Updates**

    ```markdown
if (self.promocodeText.text?.isEmpty == false )// && PFUser.currentUser()!["gotpromoCode"] == nil )
{
    var query1 = PFQuery(className:"_User")
    query1.whereKey("promoCode", equalTo:self.promocodeText.text!)
    query1.findObjectsInBackgroundWithBlock {
        (objects: [PFObject]?, error: NSError?) -> Void in

        if error == nil {

            PFUser.currentUser()!.setValue(self.promocodeText.text, forKey: "gotpromoCode")
            // The find succeeded.
            print("Successfully retrieved \(objects!.count) scores.")

            // Do something with the found objects
            if let objects = objects {
                for object in objects {
                    print(object.objectId)

                    PFUser.currentUser()!.setValue(object.objectId!, forKey: "senderUserId")
                    print("senderUserId is: \(object.objectId!)")

                }
            }


        } else {
            // Log details of the failure
            print("Error: \(error!) \(error!.userInfo)")
            self.displayAlert("Error!", body: "Promo Code does not exists")

        }

    }

}

To prevent premature updates, we need to make sure that all necessary API calls have completed before updating the user's properties. This ensures that any subsequent updates occur in a consistent manner.

Conclusion

By understanding how segues interact with Parse.com’s cloud-based database and taking steps to synchronize updates, you can resolve inconsistencies that may arise during transitions between view controllers. By implementing synchronous updates and ensuring that all necessary API calls complete before updating user properties, you can maintain data consistency throughout your app.

In conclusion, resolving this issue requires an in-depth understanding of how Parse.com handles updates on segues. By following the solutions outlined above, you can ensure that your app remains consistent and reliable.

Finally, by taking a thorough approach to understanding and addressing potential issues, you can build robust mobile apps that provide seamless user experiences across various platforms.

Last modified on 2025-05-01