Delete Realm Object By Value

Question

I started trying Realm for IOS, so I created two classes:

Files Model

import Foundation
import RealmSwift

    class FilesModel: Object {
        
        @objc dynamic var id : Int = 0
        @objc var fileName = ""
        @objc dynamic var dateOfCreation = Date()
        @objc dynamic var dateOfModification = Date()
        @objc dynamic var type = ""
        var file = List<Data>()
    
    }

Groups Model

import Foundation
import RealmSwift

class GroupsModel: Object {
    
    @objc dynamic var id : Int = 0
    @objc dynamic var name = ""
    @objc dynamic var dateOfCreation = Date()
    @objc dynamic var dateOfModification = Date()
    @objc dynamic var filesCount = Int()
    var files = List<FilesModel>()
    
    override static func primaryKey() -> String? {
        return "id"
    }
}

Now the thing is I am copying files into groups model file Object but I need to delete the parent object. think of it as a move I am moving files into the folder. what I have done is I save a copy of the file into the folder and delete the file from outside the folder.

Problem

when I delete the file outside the folder it will also delete the file inside.

My understanding of the problem

classes is a reference type so I am copying reference. So when I delete the reference it will delete the file from the whole project.

I have tried many solutions like deep copy and detached. Thanks in Advance.

Jay · Accepted Answer · 2021-11-30 19:33:22Z

2

The issue is this statement

I am moving files into the folder

While that may be what you want to do, the objects you're moving aren't actually being moved. When you add a managed object to a a List property, it adds a reference to the object, not the object itself.

In other words, when a FilesModel is added to a GroupsModel files List property, it's a reference to the object. If you delete the FilesModel, it will also be gone from the List. But, removing it from the List does not change the original object.

However, Lists can also contain Embedded Objects - an embedded object only ever exists within it's parent object. Perhaps that would be an option?

So like this. Here's a couple of models

class FileModel: EmbeddedObject {
    @Persisted var fileName = ""
}

class GroupsModel: Object {
    @Persisted var files = List<FilesModel>()
}

Then instantiate a group and add a couple of file objects to it

let group = GroupsModel()

let f0 = FileModel()
f0.fileName = "some filename"

let f1 = FileModel()
f1.fileName = "another filename"

group.files.append(objectsIn: [f0, f1])

results in a group with two files that only ever appear within that group.

Another option is to simply make a copy of the object

let objectCopy = MyObject(value: objectToCopy)

and then add the objectCopy to your Groups model. But again, by doing that Realm will instantiate the objectCopy and actually add it back to Realm (possibly overwriting the original object).

answered Nov 30, 2021 at 19:33

Jay

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3 Comments

Muhammad Ahmad Over a year ago

hi, Jay Thank you so much for the answer. It helped me ALOT. but i am still facing the issue with is i have saved data in EmbeddedObject but i didn't find anything on how to read data from EmbeddedObject

Jay Over a year ago

@MuhammadAhmad An embedded object is just an object and is 'read' like any other object. So for example if you wanted to read a property of the first embedded object from a group, as shown in my answer, read the group from Realm and it would be let fileName = group.files[0].fileName.

Muhammad Ahmad Over a year ago

Thank You So Much. You Are a Saviour. @Jay

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