SwiftUI Query Realm Database-CodePudding

In my Realm DB for ChatMessage I have the following data object:

When i follow the tutorial on retrieving data/query :

        let realm = try! Realm()
        let specificPerson = realm.object(ofType: ChatMessage.self, 
forPrimaryKey:  ObjectId("6369ee9db15ac444f96eb5d6"))
        print(specificPerson!.author as String)

I receive fatal error Nil, it cannot find anything. from the line

        print(specificPerson!.author as String)

LiveChat/ChatView.swift:59: Fatal error: Unexpectedly found nil while unwrapping an Optional value

When I do a broader query for all,

    let chatM = realm.objects(ChatMessage.self)
    print(chatM)
    print(type(of: chatM))

I receive empty object

Results<ChatMessage> <0x7fe4d163efa0> (

)
Results<ChatMessage>

I am adding the Chat messages Via

    @ObservedResults(ChatMessage.self, 
sortDescriptor: SortDescriptor(keyPath: "timeStamp", ascending: true)) var messages


    private func addMessage(){
    let message = ChatMessage(room: room, author: userName, text: messageText)
    $messages.append(message)
    messageText = ""
}

CodePudding user response：

Regarding your updated code:

So yes, you are indeed creating the objects (using the .append(_:) method on an @ObservedResults collection) in a correct way. This means that you are likely opening the wrong realm database when you're querying for the objects. Please have a look at Realm's documentation regarding realm configuration, specifically on how to set the default configuration. Calling try! Realm() without any parameters will use this default configuration to open the database.

Original reply

If let chatM = realm.objects(ChatMessage.self) returns an empty Results object, the realm you're querying does not contain any objects of the ChatMessage type. It's as simple as that. Logically, let specificPerson = realm.object(ofType: ChatMessage.self, forPrimaryKey: ObjectId("6369ee9db15ac444f96eb5d6")) would then also return nil.

Without seeing how and where you're creating the missing ChatMessage objects, it's hard to say what's going wrong. Some common missteps:

You are querying the wrong realm database: If you are only every accessing realm through let realm = try! Realm() this shouldn't be a problem.
You haven't actually added any ChatMessage object to the realm database: Simply initializing an object is not enough, You need to explicitly add objects to the Realm database using either Realm.create() or Realm.add():

let realm = try! Realm()
let exampleObject = ChatMessage()
print(realm.objects(ChatMessage.self).count) // Prints "0"

// Add to the realm using either create() or add()
realm.add(exampleObject)

print(realm.objects(ChatMessage.self).count) // Prints "1"