MutationEvent.decodeModel don't decode LazyReference on delete mutation

[gbitaudeau]

Describe the bug

Consider the sample schema (given there : https://docs.amplify.aws/lib/datastore/relational/q/platform/ios/#updated-schema )

enum PostStatus {
  ACTIVE
  INACTIVE
}

type Post @model @auth(rules: [{allow: public}]) {
  id: ID!
  title: String!
  rating: Int!
  status: PostStatus!
  # new field with @hasMany
  comments: [Comment] @hasMany
}

# new model
type Comment @model {
  id: ID!
  content: String
  post: Post @belongsTo
}

I use the LazyReference (using generatemodelsforlazyloadandcustomselectionset option for codegen)

When I use Amplify.DataStore.observe on Comment, if a comment is deleted, the post is not well set on it using MutationEvent.decodeModel, so there is no way to know which post lost a comment.

var postsSubscription:  AmplifyAsyncThrowingSequence<MutationEvent>?

// Then in the body of your code, subscribe to the subscription
func subscribeToPosts() async {
    let commentsSubscription = Amplify.DataStore.observe(Comment.self)
    self. commentsSubscription = commentsSubscription

    do {
        for try await changes in commentsSubscription {
            let comment = try change.decodeModel(as: Comment.self)
            let post = try await comment.post //eror here
        }
    } catch {
        print("Subscription received error: \(error)")
    }
}

Steps To Reproduce

Steps to reproduce the behavior:
1. Setup an env with the previously given code
2. Delete a comment

Expected behavior

The LazyReference must load successfully using let post = try await comment.post

Amplify Framework Version

2.19.0

Amplify Categories

DataStore

Dependency manager

Swift PM

Swift version

5.9

CLI version

12.4.0

Xcode version

15.0

Relevant log output

No response

Is this a regression?

No

Regression additional context

No response

Platforms

iOS

OS Version

iOS 17.0.1

Device

iPhone 14 Pro

Specific to simulators

No response

Additional context

I found a workaround in the generated Comment.init(from decoder: Decoder), I replaced:

_post = try values.decodeIfPresent(LazyReference<Post>.self, forKey: .post) ?? LazyReference(identifiers: nil)

with

_post = try values.fixDecodeLazyReference(type: LazyReference< Post >.self, forKey: . post)

And I added the following extension:

extension KeyedDecodingContainer {
    func fixDecodeLazyReference<T>(type: LazyReference<T>.Type, forKey key: Key) throws -> LazyReference<T> {
        if let identifiers = try? self.decodeIfPresent([LazyReferenceIdentifier].self, forKey: key) {
            return LazyReference(identifiers: identifiers)
        }
        if let result = try self.decodeIfPresent(type, forKey: key) {
            return result
        }
            
        return LazyReference(identifiers: nil)
    }
}

[harsh62]

Thanks for opening the issue. Our team will look into it and provide an update on the issue.

[harsh62]

Hey @gbitaudeau .. Sorry for the delay. I wanted to ask you further if this is still a problem? I tried this on a latest version of Amplify and everything seems to be working fine.

Adding of the post and comment.

            var post = Post(
                id: "1",
                title: "1",
                status: .draft,
                content: "1")
            let comment = Comment(id: "1", content: "1", post: post)

                try await Amplify.DataStore.save(post)
                try await Amplify.DataStore.save(comment)

Deleting of the comment

                var post = try await Amplify.DataStore.query(Post.self).first!
                try await post.comments!.fetch()
                try await Amplify.DataStore.delete(post.comments!.first!)

Following is my observe query snippet

    // You must hold a reference to your subscription.
    var postsSubscription:  AmplifyAsyncThrowingSequence<MutationEvent>?

    // Then in the body of your code, subscribe to the subscription
    func subscribeToPosts() async {
        let postsSubscription = Amplify.DataStore.observe(Comment.self)
        self.postsSubscription = postsSubscription

        do {
            for try await changes in postsSubscription {
                // handle incoming changes
                if changes.mutationType == "delete" {
                    let comment = try changes.decodeModel(as: Comment.self)
                    let post = try await comment.post
                    print("Subscription received mutation: \(changes)")
                }

            }
        } catch {
            print("Subscription received error: \(error)")
        }
    }

Finally, I don't understand how when decoding a post in the comments with [LazyReferenceIdentifier].self works?

If this is still an issue, would you be able to share the entire code snippet end to end that has the problem so that I can further investigate the issue.

Just FYI, I am using the latest version of Amplify Swift and Amplify CLI.

Thanks.

[gbitaudeau]

Hi @harsh62 , sorry, I try again on my side and the problem still occurs, but I didn't give you the right steps to reproduce it.

Your code is good.
The problem only occurs when I delete a comment on another device or using this mutation in Amplify studio :

mutation MyMutation {
  deleteComment(input: {id: "XXX", _version: 1}) {
    _deleted
    _lastChangedAt
    _version
    createdAt
    content
    id
    post {
      id
      _deleted
    }
    updatedAt
  }
}

Hope with this you can reproduce it.

[harsh62]

@gbitaudeau I have a potential fix ready that seems to be working correctly for me. Would you be able to validate the fix on my working branch (named: 3252). The PR is also linked to the issue for your reference.

[gbitaudeau]

Hi @harsh62 tests are ok on my side 👍 on your branch.

[harsh62]

@gbitaudeau A fix for the issue has been released in https://github.com/aws-amplify/amplify-swift/releases/tag/2.26.2. Thanks for your patience.

[github-actions]

⚠️COMMENT VISIBILITY WARNING⚠️

Comments on closed issues are hard for our team to see.
If you need more assistance, please open a new issue that references this one.
If you wish to keep having a conversation with other community members under this issue feel free to do so.