Send only changed properties to cloud by default when updating object

[mtrezza]

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

The Parse Swift SDK requires additional code overhead and developer considerations when updating objects. Specifically, to send only changed properties to the server, the SDK requires the developer to create an object clone from ParseObject.mergeable and override an internal method ParseObject.merge . The same behavior is achieved by other Parse SDKs without these efforts.

The disadvantages are:

• Developer needs to manually maintain custom properties in the overridden ParseObject.merge method. For example, if a new custom property is added to the object but not to the internal method, it creates data inconsistencies that may lead to bugs that are difficult to track down.
• Adds code complexity for what is supposed to be one of the simplest operations - updating an object.

Feature / Enhancement Description

The Parse Swift SDK should send only the changed properties to the server by default. Without requiring the developer to override an internal method of ParseObject and without having to clone the object from ParseObject.mergeable.

Example Use Case

The following examples compare how to update a saved object in the Parse ObjC SDK vs. the Parse Swift SDK.

// Parse ObjC SDK
PFObject *obj = [PFObject objectWithClassName:@"Example"];
obj[@"key"] = @"value1";
[obj save];
obj[@"key"] = @"value2";
[obj save];

// Parse Swift SDK
struct Example: ParseObject {
  var objectId: String?
  var createdAt: Date?
  var updatedAt: Date?
  var ACL: ParseACL?
  var originalData: Data? 
  var key: String?

  func merge(with object: Self) throws -> Self { 
    var updated = try mergeParse(with: object) 
    if updated.shouldRestoreKey(\.key, original: object) { 
      updated.key = object.key 
    }
    return updated
  }
}

let obj = Example()
obj.key = "value1"
obj.save()
var objMergable = obj.mergeable
objMergable.key = "value2"
objMergable.save()

Alternatives / Workarounds

n/a

References

• Partially updating an object sends the full object to the server #242

[parse-github-assistant]

Thanks for opening this issue!

• 🎉 We are excited about your ideas for improvement!

[mtrezza]

PR #406 was a great step towards simplification.

To follow up on the example above, the code after the PR would be:

// Parse ObjC SDK
PFObject *obj = [PFObject objectWithClassName:@"Example"];
obj[@"key"] = @"value1";
[obj save];
obj[@"key"] = @"value2";
[obj save];

// Parse Swift SDK
struct Example: ParseObject {
  var objectId: String?
  var createdAt: Date?
  var updatedAt: Date?
  var ACL: ParseACL?
  var originalData: Data? 
  var key: String?
}

let obj = Example()
obj.key = "value1"
obj.save()
let updatedObj = try obj.key.set(\.key, to: "value2")
let savedUpdatedObj = try await updatedObj.save()

// or without declaring new vars for every state
var obj = Example()
obj.key = "value1"
obj.save()
obj = try obj.key.set(\.key, to: "value2")
obj = try await obj.save()

Is that correct?

If so, I think we can reword the warning in the migration guide, but not remove it completely. Because a developer still has to keep in mind that there is a special approach (even though simplified thanks to #406) needed to only send updated keys to the server, and they cannot simply use obj.key = "value2".