Calling Mapper().toJSON(object) modifies the underlying object properties

[ldiqual]

Calling Mapper().toJSON(object) modifies the underlying object properties

[thacilima]

I also had this problem just when writing the id (realm object primary key) to json.

My solution bellow:

if map.mappingType == .ToJSON {
    var id = self.id
    id <- map["id"]
}
else {
    id <- map["id"]
}

In this solution you don't need an extra variable and the id will be in your json

[dmorrow]

Using the clone functionality in Realm, you can make this work

let preferencesCopy: Preferences = Preferences(value: preferences)
preferencesCopy.toJSON()

[tristanhimmelman]

Hey there,

Weird issue indeed. It took me a little while to track down...

The custom operator that ObjectMapper uses is used for both Serialization and Deserialization of JSON. In deserialization the object on the left of the operator is being modified but not in serialization. Because of this the object being passed on the left side of the operator gets the flag "inout" in the operator function definition. This tells the compiler that the variable is modifiable within the scope of the function. This seems to be what Realm is unhappy about even though the object is not being modified during serialization. When I removed the flag and the deserialization code, the crash no longer happens...

I can't think of a solution off the top of my head to solve this issue. I will put some more thought into it to see if I can come up with a solution.

Tristan

[zocario]

Hi @tristanhimmelman, I am having the exactly same issue in my project.
During serialization of my Realm objects the App crashes as Realm thinks I am modifying the object when the mapping function is called.

As the issue is closed I guess you've found a solution for this problem?
I am using Xcode 6.3 beta with Swift 1.2, so I am on the "swift-1.2" branch, maybe the fix is not on it?

Enzo

[tristanhimmelman]

Hi @zocario, no unfortunately I have not come up with a solution to this problem yet.

[zocario]

Did you try to talk with Realm guys to find a solution?
@ldiqual Have you made an issue in the Realm-Cocoa repository about this?

[tristanhimmelman]

No I have not contacted them.

I believe the crash occurs because ObjectMapper defines the <- functions using the inout flag. For example:

public func <- <T>(inout left: T, right: Map)

This function is used both for parsing and writing JSON, yet the inout requirement is only necessary when parsing the JSON. Unfortunately I haven't come up with a nice way to split up the mapping functions so that inout isn't present when writing JSON.

[zocario]

Thanks for your precisions, I've just created and issue on the Realm repository to see if they have any suggestions that could be helpful to solve this problem.

[segiddins]

You're correct in the guess that the issue is the spurious inout flag.

[zocario]

As I said in the Realm issue, I'll go with Mantle because I need a full compatibility with Realm, and solving this inout flag issue would mean change the design of your library...
Thanks for your support.

[empty]

I'm also running into this issue. It would be great if ObjectMapper was compatible with Realm.

[schmidan]

[edit] Ha, just now saw this comment/solution #294 [/edit]

If anyone runs into this again. We adopted a quick work-around until we move to another solution:

import ObjectMapper
class Event: Object, Mappable {
    dynamic var mappingIdentifier = "EVENT_NO_ID" {
        didSet {
            realmIdentifier = mappingIdentifier
        }
    }
    dynamic var realmIdentifier = "EVENT_NO_ID"

    func mapping(map: Map) {
       mappingIdentifier <- map["id"]
       ...
    }

    override static func primaryKey() -> String? {
        return "realmIdentifier"
    }
}

We just make sure, that the mapped property isnt the realms primary key.
ugly but in our case so far functional.

[felipowsky]

Workaround:

func mapping(map: Map) {
        var opened = false
        if let realm = self.realm where !realm.inWriteTransaction {
            realm.beginWrite()
            opened = true
        }
        defer { if opened { map.mappingType == .FromJSON ? try! self.realm?.commitWrite() : self.realm?.cancelWrite() } }

        self.name <- map["name"]
        // ...
}

It should be used with caution because it might commit implicit changes to your database.

[geodesicer]

the workaround I use is the following:

class RBase: Object, Mappable {
dynamic var id = NSUUID().UUIDString
dynamic var idz = "" {
didSet {
idz = id
}
}

override class func primaryKey() -> String? {
    return "id"
}

func mapping(map: Map) {
    ....
    idz <- map["id"]
    idz <- map["idz"]
}

Also see the complete code in Subclassing and Realm #462

[morgz]

I get issues with any Realm backed attribute not just the primary key because the <- operator makes realm think we're modifying the underlying object. Shame, I like objectMapper DSL but for JSON serialising a Realm object it appears to be pretty incompatible without starting a write transaction.

[geodesicer]

So far I have only seen that problem when when modifying the "id"-property, and we write a new JSON-file at most property changes due to specific requirements, i.e. using two different database engines and using the JSON-file as a "secure" transport mechanism between databases.

[nabbestemmia]

Thank you guys, I thought to be alone in this situation!

[alexanderkhitev]

@thacilima Hello!
I use your code in Swift 3, but I get error libc++abi.dylib: terminating with uncaught exception of type NSException when I call the let JSON = Mapper().toJSON(messageModel)

MessageModel snippet code

  override static func primaryKey() -> String? {
        return "id"
    }

    func mapping(map: Map) {
        if map.mappingType == .toJSON {
            var id = self.id
            id <- map["id"]
        } else {
            id <- map["id"]
        }
//        id <- map["id"]
        date <- map["date"]
        message <- map["message"]
        imageData <- map["imageData"]
        imageURL <- map["imageURL"]
        senderID <- map["senderID"]
        conversationID <- map["conversationID"]
        isIncoming <- map["isIncoming"]
        isNew <- map["isNew"]
        messageStatus <- map["messageStatus"]
    }

    required convenience init?(map: Map) {
        self.init()
    }

[juanrodriguezarc]

try using a realm transaction and don't use a primary key
let realm = try! Realm() try! realm.write({ print("'HERE'",Mapper().toJSONString(user!, prettyPrint: true)) })

[liangsay]

i try using this one,it's OK, you can try
https://github.com/APUtils/ObjectMapperAdditions