Read & Write Data - Swift SDK

Find a Specific Object by Primary Key

Query All Objects of a Given Type

Filter Queries Based on Object Properties

A filter selects a subset of results based on the value(s) of one or more object properties. Realm Database provides a full-featured query engine that you can use to define filters.

Filter on Object ID Properties

The types in your predicate must match the types of the properties. Avoid comparing ObjectId properties to strings, as Realm Database does not automatically convert strings to ObjectIds.

Sort Query Results

A sort operation allows you to configure the order in which Realm Database returns queried objects. You can sort based on one or more properties of the objects in the results collection. Realm Database only guarantees a consistent order of results if you explicitly sort them.

Query a Relationship

You can query through a relationship the same way you would access a member of a regular Swift or Objective-C object.

Query an Inverse Relationship

You can query through an inverse relationship the same way you would access a member of a regular Swift or Objective-C object.

Aggregate Data

You can use Realm's aggregation operators for sophisticated queries against list properties.

Chain Queries

Because results are lazily evaluated, you can chain several queries together. Unlike traditional databases, this does not require a separate trip to the database for each successive query.

Create a New Object

Initialize Objects with a Value

You can initialize an object by passing an initializer value to Object.init(value:). The initializer value can be a key-value coding compliant object, a dictionary, or an array containing one element for each managed property.

You can even initialize related or embedded objects by nesting initializer values:

Create an Object with JSON

Realm does not directly support JSON, but you can use JSONSerialization.jsonObject(with:options:) to convert JSON into a value that you can pass to Realm.create(_:value:update:).

Nested objects or arrays in the JSON map to to-one or to-many relationships.

The JSON property names and types must match the destination object schema exactly. For example:

• float properties must be initialized with float-backed NSNumbers.
• Date and Data properties cannot be inferred from strings. Convert them to the appropriate type before passing to Realm.create(_:value:update:).
• Required properties cannot be null or missing in the JSON.

Realm ignores any properties in the JSON not defined in the object schema.

Copy an Object to Another Realm

Perform a Background Write

You can add, modify, or delete objects in the background using writeAsync.

With async write, you don't need to pass a thread-safe reference or frozen objects across threads. Instead, call realm.writeAsync. You can provide a completion block for the method to execute on the source thread after the write completes or fails.

Things to consider when performing background writes:

• Async writes block closing or invalidating the realm
• You can explicitly commit or cancel transactions

let realm = try! Realm()
// Query for a specific person object on the main thread
let people = realm.objects(Person.self)
let thisPerson = people.where {
    $0.name == "Dachary"
}.first
// Perform an async write to add dogs to that person's dog list.
// No need to pass a thread-safe reference or frozen object.
realm.writeAsync {
    thisPerson?.dogs.append(objectsIn: [
        Dog(value: ["name": "Ben", "age": 13]),
        Dog(value: ["name": "Lita", "age": 9]),
        Dog(value: ["name": "Maui", "age": 1])
    ])
} onComplete: { _ in
    // Confirm the three dogs were successfully added to the person's dogs list
    XCTAssertEqual(thisPerson!.dogs.count, 3)
    // Query for one of the dogs we added and see that it is present
    let dogs = realm.objects(Dog.self)
    let benDogs = dogs.where {
        $0.name == "Ben"
    }
    XCTAssertEqual(benDogs.count, 1)
}

Modify an Object

You can modify properties of a Realm object inside of a write transaction in the same way that you would update any other Swift or Objective-C object.

Update Properties with Key-value Coding

Object, Result, and List all conform to key-value coding. This can be useful when you need to determine which property to update at runtime.

Applying KVC to a collection is a great way to update objects in bulk. Avoid the overhead of iterating over a collection while creating accessors for every item.

let realm = try! Realm()
let allDogs = realm.objects(Dog.self)
try! realm.write {
    allDogs.first?.setValue("Sparky", forKey: "name")
    // Move the dogs to Toronto for vacation
    allDogs.setValue("Toronto", forKey: "currentCity")
}

Upsert an Object

An upsert either inserts or updates an object depending on whether the object already exists. Upserts require the data model to have a primary key.

You can also partially update an object by passing the primary key and a subset of the values to update:

Delete an Object

Delete Multiple Objects

Delete All Objects of a Specific Type

Delete All Objects in a Realm