Subclass currently has no primary key relationship - ios

Question

I have JSON that looks like this, which returns a list of Posts:
[
{
"id" : 1,
"message": "Hello"
"urls" : {
"png" : "https://example.com/image.png",
"jpg" : "https://example.com/image.jpg",
"gif" : "https://example.com/image.gif"
}
}
]
As you can see, I need to make two classes. One for the parent object (Post), and one for the object "urls" (PostUrls).
I've done that like so:
class Post: Object, Decodable {
#objc dynamic var id = 0
#objc dynamic var message: String? = nil
#objc dynamic var urls: PostUrls? = nil
override static func primaryKey() -> String? {
return "id"
}
private enum PostCodingKeys: String, CodingKey {
case id
case message
case urls
}
convenience init(id: Int, message: String, urls: PostUrls) {
self.init()
self.id = id
self.message = message
self.urls = urls
}
convenience required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: PostCodingKeys.self)
let id = try container.decode(Int.self, forKey: .id)
let message = try container.decode(String.self, forKey: .message)
let urls = try container.decode(PostUrls.self, forKey: .urls)
self.init(id: id, message: message, urls: urls)
}
required init() {
super.init()
}
}
And
#objcMembers class PostUrls: Object, Decodable {
dynamic var png: String? = nil
dynamic var jpg: String? = nil
dynamic var gif: String? = nil
private enum PostUrlsCodingKeys: String, CodingKey {
case png
case jpg
case gif
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: PostUrlsCodingKeys.self)
png = try container.decodeIfPresent(String.self, forKey: .png)
jpg = try container.decodeIfPresent(String.self, forKey: .jpg)
gif = try container.decodeIfPresent(String.self, forKey: .gif)
super.init()
}
required init() {
super.init()
}
}
But, the problem is that I have no relationship between Post and PostUrls, since there is no primary key to connect the two. Further, this also means that I currently won't be able to control duplicates inside the PostUrls table.
So my question is: how can I create a relationship between the two tables, and prevent duplicates in the PostUrls table?

Answer 1

In this case, you do have a relationship between those objects. Object Post contains object PostUrls. Realm does not require a primary key to have this kind of relationship, because it creates a primary key behind the scenes. So it uses it, even though you can't access it.
To manually set a primaryKey you have to override a func called primaryKey()
#objcMembers class DBFilterModel: Object {
// MARK: Properties
dynamic var id: Int = 0
override public static func primaryKey() -> String? {
return "id"
}
}
This way you tell to realm that you want this property to be used as a Unique Key.
To prevent duplicating them, there are 2 ways. First - try to find an object with that id already existing in your database, if it exists - don't create it.
Second - by adding conflicts handlers to Realm's save methods. You can set that objects with same ID's will be just modified, but not duplicated. Or you could say that you want to throw an error when you try to insert a duplicated object.
realm.add(objects, update: update ? .modified : .error)

Answer 2

The question has two questions within
How do you create a relationship between the two 'tables'
prevent duplicates
Let me address 1)
Start with a class to hold the image type (.jpg etc) and then the url
class ImageUrlClass: Object {
#objc dynamic var imageType = ""
#objc dynamic var imageUrl = ""
}
and then the main class which handles decoding
class Post: Object, Decodable {
#objc dynamic var id: Int = 0
#objc dynamic var message: String = ""
let urlList = List<ImageUrlClass>()
...edited for brevity
convenience init(id: Int, message: String, urls: [String: String]) {
self.init()
self.id = id
self.message = message
//create a ImageUrlClass from each dictionary entry
for url in urls {
let key = url.key
let value = url.value
let aUrl = ImageUrlClass(value: ["imageType": key, "imageUrl": value])
self.urlList.append(aUrl)
}
}
convenience required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: PostCodingKeys.self)
let id = try container.decode(Int.self, forKey: .id)
let message = try container.decode(String.self, forKey: .message)
let urls = try container.decode([String: String].self, forKey: .urls)
self.init(id: id, message: message, urls: urls)
}
}
The above will create a Post object with a List property that contains the image types and urls (a List behaves very similar to an array)
You could further this by adding a LinkingObjects property to the ImageUrlClass which would automagically create an inverse relationship to the Post object when objects are added to the List. Not sure if you need that but it's available.
You can this do this to print out the post properties
let decoder = JSONDecoder()
let post = try! decoder.decode(Post.self, from: encodedData)
print(post.id)
print(post.message)
for url in post.urlList {
let a = url.imageType
let b = url.imageUrl
print(a,b)
}
which would results in an output like this
1
Hello
jpg https://example.com/image.jpg
png https://example.com/image.png
gif https://example.com/image.gif