Core Data Fetch Requests In Swift

Core Data is a powerful database framework for iOS and macOS apps. This post presents examples of making queries using fetch requests for Core Data objects in Swift:

1. Get Object By ID
2. Fetch A Single Object
3. Filter Fetch Request With Predicate
4. Filter Predicate With Multiple Conditions
5. Fetch All Objects Of One Entity
6. Fetch Request Multiple Entities

Note: in this post persistentContainer will be used to refer to an initialized instance of NSPersistentContainer.

Get Object By ID

To get an object by ID in Core Data, use the existingObject(with:) function on an instance of NSManagedObjectContext:

// Get the managed object ID of the object
let managedObject = // ... an NSManagedObject
let managedObjectID = managedObject.objectID

// Get a reference to a NSManagedObjectContext
let context = persistentContainer.viewContext

// Get the object by ID from the NSManagedObjectContext
let object = try context.existingObject(
    with: managedObjectID
)

Fetch A Single Object

To fetch an object in Core Data, limit a NSFetchRequest to return one result. Then, use the fetch(_:) function on an instance of NSManagedObjectContext:

// Configure a fetch request to fetch at most 1 result
let fetchRequest = // An NSFetchRequest
fetchRequest.fetchLimit = 1

// Get a reference to a NSManagedObjectContext
let context = persistentContainer.viewContext

// Fetch a single object. If the object does not exist,
// nil is returned
let object = try context.fetch(fetchRequest).first

Filter Fetch Request With Predicate

To add a filter to a Core Data fetch request, add a predicate. Then, use the fetch(_:) function on an instance of NSManagedObjectContext:

// Create a fetch request with a string filter 
// for an entity’s name  
let fetchRequest: NSFetchRequest<Entity> 
fetchRequest = Entity.fetchRequest()

fetchRequest.predicate = NSPredicate(
    format: "name LIKE %@", "Robert"
)

// Get a reference to a NSManagedObjectContext
let context = persistentContainer.viewContext

// Perform the fetch request to get the objects
// matching the predicate
let objects = try context.fetch(fetchRequest)

You can see more examples of filter fetch requests with NSPredicate in the following article:

Swift Core Data String Queries

Learn how to find an exact string, regex search, and more in Core Data.

Advanced SwiftRobert Pieta

Filter Predicate With Multiple Conditions

A compound predicate can contain multiple conditions to create a complex fetch request in Core Data. Set a compound predicate on a fetch request and then use the fetch(_:) function on an instance of NSManagedObjectContext:

// Create a fetch request with a compound predicate
let fetchRequest: NSFetchRequest<Entity> 
fetchRequest = Entity.fetchRequest()

// Create the component predicates
let namePredicate = NSPredicate(
    format: "name LIKE %@", "Robert"
)

let planetPredicate = NSPredicate(
    format: "country = %@", "Earth"
)

// Create an "and" compound predicate, meaning the 
// query requires all the predicates to be satisfied.
// In other words, for an object to be returned by 
// an "and" compound predicate, all the component 
// predicates must be true for the object.
fetchRequest.predicate = NSCompoundPredicate(
    andPredicateWithSubpredicates: [
        namePredicate, 
        planetPredicate
    ]
)

// Get a reference to a NSManagedObjectContext
let context = persistentContainer.viewContext

// Perform the fetch request to get the objects 
// matching the compound predicate
let objects = try context.fetch(fetchRequest)

Fetch All Objects Of One Entity

The fetchRequest() function is available on subclasses of NSManagedObject in Core Data. Using fetchRequest() on a Core Data entity creates a fetch request for all objects of that entity type:

// Create a fetch request for a specific Entity type
let fetchRequest: NSFetchRequest<Entity> 
fetchRequest = Entity.fetchRequest()

// Get a reference to a NSManagedObjectContext
let context = persistentContainer.viewContext

// Fetch all objects of one Entity type
let objects = try context.fetch(fetchRequest)

Fetch Request Multiple Entities

One way to create a fetch request targeting multiple entities is to add a shared parent class to multiple entities. For example, a NamedEntity can be created with a String property name.

Then, the Parent entity can be set to NamedEntity in the Entity Inspector in Xcode:

In this example, NamedEntity is set as the parent class of the Business entity and Brand entity. The fetch request in the example will return Business entities and Brand entities with a name property equal to "Apple".

// Create a fetch request for a NamedEntity
let fetchRequest: NSFetchRequest<NamedEntity> 
fetchRequest = NamedEntity.fetchRequest()

// Add a predicate for entities with a name 
// attribute equal to "Apple"
fetchRequest.predicate = NSPredicate(
    format: "name LIKE %@", "Apple"
)

// Get a reference to a NSManagedObjectContext
let context = persistentContainer.viewContext

// Perform the fetch request to get the objects 
// matching the predicate
let objects = try context.fetch(fetchRequest)

// Handle multiple entity types
for object in objects {
    if let object = object as? Business {
        print("Business:", object.name)
    }
    else if let object = object as? Brand {
        print("Person:", object.name)
    }
}

Core Data Queries in Swift

That's it! By using NSFetchRequest and NSPredicate you can make queries and filter by ID, predicate, entity in Core Data using Swift.