What is predicate in Core Data?

What is predicate in Core Data?

The predicate instance constrains the selection of objects the NSFetchRequest instance is to fetch. If the predicate is empty—for example, if it is an AND predicate whose array of elements contains no predicates—the request has its predicate set to nil . For more about predicates, see Predicate Programming Guide.

What are relationships in Core Data?

Relationship Fundamentals A relationship specifies the entity, or the parent entity, of the objects at the destination. This entity can be the same as the entity at the source (a reflexive relationship).

What is inverse relationship in Core Data?

Inverse relationships enable Core Data to propagate change in both directions when an instance of either the source or destination type changes. Every relationship must have an inverse. When creating relationships in the Graph editor, you add inverse relationships between entities in a single step.

How predicate is used in Core Data?

Core Data fetch requests can use predicates in SwiftUI just like they can with UIKit, all by providing a predicate property to your @FetchRequest property wrapper.

What is the predicate example?

A predicate is the part of a sentence, or a clause, that tells what the subject is doing or what the subject is. Let’s take the same sentence from before: “The cat is sleeping in the sun.” The clause sleeping in the sun is the predicate; it’s dictating what the cat is doing. Cute!

Is Core Data relational?

What you need to know is that Core Data is not a database. That said, when working with Core Data it acts as a relational database hence the confusion. Core Data is a persistence solution for Apple’s platforms and it supports several types of persistent stores, including SQLite.

How predicate is used in core data?

What is NSSet in Swift?

The NSSet , NSMutableSet , and NSCountedSet classes declare the programmatic interface to an unordered collection of objects. NSSet declares the programmatic interface for static sets of distinct objects. In Swift, use this class instead of a Set constant in cases where you require reference semantics.

Should have an inverse Core Data?

A quick Google suggests you should use them: An inverse relationship doesn’t just make things more tidy, it’s actually used by Core Data to maintain data integrity. You should typically model relationships in both directions, and specify the inverse relationships appropriately.

How to tell core data that we’ve updated the relationship?

There is no need to tell Core Data that we’ve updated the relationship. Core Data keeps track of the mutable set that it gave us and updates the relationship. You can delete a relationship by invoking setValue (_:forKey:), passing in nil as the value and the name of the relationship as the key.

Should core data be sorted or unsorted?

Most people new to Core Data expect a sorted array, but Core Data returns a set, which is unsorted. Working with sets has its advantages as you’ll learn later. Enough with the theory, open the project from the previous article or clone it from GitHub.

How does core data handle inverse relationships?

Core Data creates this relationship for us. If a relationship has an inverse relationship, then Core Data takes care of this automatically. You can verify this by asking newAddress for its persons. Updating a relationship isn’t difficult either.

What is the meaning of “relationships”?

Relationships are, just like attributes, accessed using key-value coding. Remember that the data model we created earlier in this series defines a Person entity and an Address entity. A person is linked to one or more addresses and an address is linked to one or more persons.