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iosswiftcore-datarelationships

Creating core data for chat app in swift

I’m developing an application similar to an simple chat app and I need to use core data to save/fetch the chats based on specific user. I have now successfully created a model to save users, now I need to link them to their chats. For Saving user data I’ve created Entity UserData and below are my swift files

UserData+CoreDataProperties.swift

import Foundation
import CoreData

extension UserData {

    @NSManaged var firstName: String?
    @NSManaged var userStatus: String?
    @NSManaged var userId: String?
    @NSManaged var userStatus: String?
    @NSManaged var lastName: String?
    @NSManaged var profilePic: String?

}

UserData.swift

class UserData: NSManagedObject {


    convenience init(WithDictionary dict:NSDictionary){


        let appDelegate =  UIApplication.sharedApplication().delegate as! AppDelegate

        let managedContext = appDelegate.managedObjectContext

        let newEntity =  NSEntityDescription.entityForName("UserData", inManagedObjectContext:managedContext)

        // initializer on NSManagedObject class
        self.init(entity: newEntity!, insertIntoManagedObjectContext: managedContext)

        self.userId =  (dict.valueForKey(ID) != nil) && !(dict.valueForKey(ID) is NSNull)
            ? dict.valueForKey(ID) as! String
            : ""

       //similary initializing other variables

        //Saving to database

        do {
            try managedContext.save()

        } catch let error as NSError  {
            print("Could not save \(error), \(error.userInfo)")
        }

    }

I was able to successfully save the user list using this class. Now I’ve created a ChatData Entity, below is its structure.

ChatData+CoreDataProperties.swift

import Foundation
import CoreData

extension ChatData {

    @NSManaged var chatId: String?
    @NSManaged var chatOwnerName: String?
    @NSManaged var chatReadStatus: Boolean?
    @NSManaged var chatText: String?
    @NSManaged var chatTimestamp: String?
    @NSManaged var chatType: String?
    @NSManaged var imageData: String?
    @NSManaged var imageUrl: String?

}

Now for each specific user I should be able to create multiple ChatData objects corresponding to particular userId. I don’t have much experience with core data. I’ve looked at some samples on creating relationship, but I’m still not sure how it works. Do I need to create a relationship? If so how should I do it to make this work?

Solution

  • You can modify UserData like this

    extension UserData {
   @NSManaged var firstName: String?
   @NSManaged var userStatus: String?
   @NSManaged var userId: String?
   @NSManaged var userStatus: String?
   @NSManaged var lastName: String?
   @NSManaged var profilePic: String?
   @NSManaged var chats: Set<ChatData>?
}

    and ChatData like this

    extension ChatData {
   @NSManaged var chatId: String?
   @NSManaged var chatOwnerName: String?
   @NSManaged var chatReadStatus: Boolean?
   @NSManaged var chatText: String?
   @NSManaged var chatTimestamp: String?
   @NSManaged var chatType: String?
   @NSManaged var imageData: String?
   @NSManaged var imageUrl: String?
   @NSManaged var user: UserData?
}

    The corresponding core data model has a one-to-many releationship from UserData to ChatData (some attributes are missing):

    enter image description here

    Some code that shows how you can create a user with two messages:

    let user=userWithName("MyName")
let chat01=chatWithText("How do you doing?")
let chat02=chatWithText("Fine.")
user?.chats=[chat01!,chat02!]
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
appDelegate.saveContext()

    with 

    func userWithName(name:String) -> UserData? {
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext
    let userEntity =  NSEntityDescription.entityForName("UserData", inManagedObjectContext:managedContext)
    let user = NSManagedObject(entity: userEntity!, insertIntoManagedObjectContext: managedContext) as! UserData
    user.firstName=name
    return user
}

func chatWithText(text:String) -> ChatData? {
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext
    let chatEntity =  NSEntityDescription.entityForName("ChatData", inManagedObjectContext:managedContext)
    let chat = NSManagedObject(entity: chatEntity!, insertIntoManagedObjectContext: managedContext) as! ChatData
    chat.chatText=text
    return chat
}