Understanding One-to-One and One-To-Many relationships While working on my latest project I have decided to write a tutorial about . Core Data Relationships between Entities Persistent Storage has become an essential part of the majority of apps that are released today. When we speak about persistency in iOS, we should only think on . This powerful tool will provide a great experience for you while managing your data storage. iOS Core Data Core Data Relationships Example For the purposes of this tutorial, I have created a simple project with Entities that will handle both and relationships. Core Data One-To-One One-To-Many There are 3 Entities created in the example: - this will be the main entity, that will have relationships with the and entities. Person Phone Friends - an entity that will keep the Person’s mobile phone information. It will be used as a relationship, assuming that the has only one phone. Phone One-To-One Person - an entity that will keep all the Person’s friends. It will be used as a One-To-Many relationship, assuming that the person has more than one friend. Friends As you can see in the above screenshot, I have already created the relationships. I will now explain to you how to that properly (it’s quite straightforward).👇 One-To-One Relationship (Person -> Phone) If you have created the Entities we can proceed with creating the relationship between Person and Phone. You will need to add 3 values in order to create a relationship. - name your relationship. Relationship - add the entity you want to establish a relationship with (in our case Phone). Destination - create an inverse relationship from Phone and pick it under Person. Apple recommends that you always add an inverse value, so never leave this empty. Inverse Part 1 (Person) Part 2 (Phone) Code Each Entity contains its own automatically generated that you can work within the code. This is one of the advantages of Core Data before others. NSManagedObject Here is an example how you can write in and its One-To-One Relationship ( ).👇 Person Phone Simple isn’t it? One-To-Many Relationship (Person -> Friends) I hope that by far you understood how relationships work. Now we will go further and create a relationship. The concept is the same as the relationship, just with some minor changes. One-To-Many One-To-One When creating a relationship, you will have to change the type to from the Data Model Inspector. This isn’t the case with because this type is set to by default_._ One-To-Many To Many One-To-One To One Code Here is an example how you can write in and its One-To-Many Relationship ( ).👇 Person Friends The NSManagedObject contains generic methods like where you can pass either a Friends object or an array of Friends_._ addToFriends() The code that you saw in this tutorial is written in the AppDelegate for simplicity and to provide faster tests, due to the predefined context and Core Data save method. NOTE: I am using Core Data relationship in my latest project: _‎HOT ODDS Each day, we generate a list of the hottest odds in the world. These are odds that have dropped the most…_apple.co ‎1x2 BET - Soccer Tips & Odds If you have liked my tutorial and it helped you, please 👏 or share this story so others can find it as well. Cheers! 🚀

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