Core data relationship in ios

One-to-Many and Many-to-Many Core Data Relationships

core data relationship in ios

Learn Swift coding for iOS with these free tutorials. In Core Data, this is represented using relationships, which are a bit like calculated properties except Core. Basics of CoreData framework, which is a tool for iOS, macOS, tvOS Than you have to get back to User entity and set relationship with Car. This is a tutorial where you'll learn how to work with predicates and relationships in Core Data. It is written by iOS Tutorial Team member.

In this case, the editor will be expecting you to change the name and select a valid type. After you create this new attribute it should look like the picture below.

That is one of the responsabilities of Core Data and it is the framework that will create the logic for your entity internally. After this we want to create a relationship between these two entities, where a task can have multiple notes. You will notice that a warning appears. This is not strictly required, but setting the inverse relationship will help Core Data ensure the consistency of the object graph when a change is made.

Initializing the Persistence Coordinator In iOS 10, you only need to specify the container name with the same name as your. Designing a simple User Interface Since the main goal of this article is not related to how we design user interfaces, I will give you a quick setup to support this article.

To start, go ahead and select the Main. It should look like the picture below. Next, we need to indicate to the Table View which object will be responsible to return objects for it.

Core Data on iOS 10, a brief overview with an Example

Going back to code, add the following instance and method into the ViewController. And with this we have a basic user interface to support this use case for Code Data. I will not extend all user interfaces to fulfill the entire model layer, but you have the idea how to propagate to additional view controllers.

Then add to your ViewController. To fetch objects from the database the best aproach, and the solution Apple wants us to use, is the NSFetchedResultsController. Fetched results controllers can fetch efficiently records from a predicate and a sort order.

Core Data on iOS 5 Tutorial: How To Work with Relations and Predicates

It can also monitor changes to objects in the associated managed object context, and report changes in the result sets to its delegate. After creating it, we will use a var of the same type to access this fetched results controller instance. Likewise, if you define a nonoptional to-many relationship from Employee to Address with a minimum count of 1, simply creating an instance of Employee does not create a new Address instance.

Inverse Relationships Most object relationships are inherently bidirectional. If a Department has a to-many relationship to the Employees who work in a Department, there is an inverse relationship from an Employee to the Department that is to-one.

The major exception is a fetched property, which represents a weak one-way relationship—there is no relationship from the destination to the source. See Weak Relationships Fetched Properties. The recommended approach is to model relationships in both directions and specify the inverse relationships appropriately.

Core Data uses this information to ensure the consistency of the object graph if a change is made see Manipulating Relationships and Object Graph Integrity. Relationship Delete Rules A relationship's delete rule specifies what should happen if an attempt is made to delete the source object. Note the phrasing if an attempt is made. If a relationship's delete rule is set to Deny, it is possible that the source object will not be deleted.

Core Data Relationships – Hacker Noon

Consider again a department's employees relationship and the effect of the different delete rules. Deny If there is at least one object at the relationship destination employeesdo not delete the source object department. One will be used to add a new bank, and the other will show the search view. You create an instance of FailedBankInfo and you populate the properties with values.

Finally, you save the context to make sure the insertion is committed to the database. If you run the application now, you should notice that the table view gets updated correctly with the new instance without requiring a call to reloadData.

This is due to the these functions, both inherited from previous versions of the project: This takes care of four possible changes to the table view: You can enable that by adding the swipe-to-delete functionality, built-in to table views.

You just need to add two methods.

One-to-Many and Many-to-Many Core Data Relationships

The first new method simply indicates which cells in the table are editable. You can either add the following code below tableView: Again, there is a commented-out section of code for this, but instead of using it, replace that code with the following: Build and run, add a few banks, and swipe one of the cells to show the delete button. Also make sure that a XIB is generated. The view will be pushed by a view controller, so you might want to visualize the space taken by a navigation bar.

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This will be displayed when necessary via code to edit dates. For the moment, place the picker outside of the visible area of the view. The Y of the picker should be set to With the picker selected, switch to the Size Inspector tab on the right sidebar and set its position as follows: Add it below the existing initWithNibName: The operation in this case is easy: Add the code for it to the end of the file but before the final end: Add it to the end of the file: Add the necessary code again to the end of the file: Add the following code below viewDidLoad: Add the code for those to the end of the file: Before showing the date picker, the first responder for all text fields is resigned, thus effectively dismissing the keyboard if it was visible.

To test your new view, you need to push it onto the navigation stack when a cell is tapped. Run the app and create a few instances of banks. Each bank record is editable, including the close date. To save data, hit the save button; to discard changes, just tap the back button.

core data relationship in ios

Notice that the date picker and the keyboard never obstruct each other. Changes are reflected in the list of banks with no need to refresh the table view. Think of the classic example of employees and departments — an employee is said to belong to a department, and a department has employees.

In database modeling, relationships can be of three types: This property is usually referred to as cardinality.

core data relationship in ios

In the example from the previous section, there is already a relation modeled in Core Data: This is a one-to-one relationship: The graphical view stresses this point by connecting the two entities with one single arrow line.

In other words, these two only have eyes for each other.

core data relationship in ios

This is just a string identifying the name of the relation. This is the target or the destination class of the relation. The answer to the question: Is the destination a single object or not? If yes, the relation is of type to-one, otherwise it is a to-many. The definition of the inverse function. It is pretty rare to find a domain where this is not needed.

core data relationship in ios

It is also a sort of logical necessity: In your example, a department can have more than one employee, so this is a to-many relation. As a general rule, a one-to-many relation has a many-to-one inverse.

Learn about Relationships with Core Data - Beginning Core Data Tutorial -