Getting started with ObjectBox Swift

Learn how to use ObjectBox NoSQL DB to persist data with swift for an Offline-first iOS app experience. ObjectBox performs well on all CRUD operations and is fully ACID compliant.

To see ObjectBox in action, you need to

1. Install ObjectBox if you haven't already.

2. Define your Entities, i.e. the classes you want to persist.

3. import ObjectBox into your source file

Define your Entities

ObjectBox uses code generation to read and write your objects instead of forcing you to inherit from a base object. To mark an object as an entity, you have two options:

• Conform to the Entity protocol or

• add // objectbox:entity before the type as an annotation for the code generator.

Then supply an ID property and parameter-less initializer init(), and you're good to go:

import ObjectBox

class ExampleEntity: Entity {
    var id: Id = 0
    
    required init() {
        // no properties, so nothing to do here, ObjectBox calls this
    }
}

That is all you need to get going. Build your project and ObjectBox's code generator will generate the boilerplate code to persist and read objects of this type.

You initialize an Id with 0 for all entities. This tells ObjectBox your object isn't persisted, yet. When you persist objects, the ID will be changed to the actual value. And once an entity has a non-zero ID, persisting changes will update the existing record instead of creating a new one.

So the ID is managed by ObjectBox. Conversely, you do not want to modify it yourself.

Initialize a Store

To create or access a database on disk, use the ObjectBox.Store class. The Store behaves much like a database connection: you keep the instance around to maintain an open connection to the data in a folder on disk. Usually for the lifetime of your app.

let store = try Store(directoryPath: "/Users/jenna/Documents/mydatabase/")

Getting "Missing argument for parameter 'model'..." here? Build the project first. Background: The ObjectBox code generator creates a second Store() initializer without the model parameter. It does this after parsing all your entities, which happens at build time. Thus, make sure to build your project at least once after declaring your entities. Otherwise Xcode's CodeSense auto-completion will not propose the right initializer in its list.

Of course, you would usually save your database in one of the standard system directories, like .applicationSupportDirectory, .documentsDirectory or .cachesDirectory:

let databaseName = "notes"
let appSupport = try FileManager.default.url(for: .applicationSupportDirectory,
                                             in: .userDomainMask,
                                             appropriateFor: nil,
                                             create: true)
                                             .appendingPathComponent(Bundle.main.bundleIdentifier!)
let directory = appSupport.appendingPathComponent(databaseName)
try? FileManager.default.createDirectory(at: directory,
                                         withIntermediateDirectories: true,
                                         attributes: nil)

let store = try Store(directoryPath: directory.path)

Working with Object Boxes

Since ObjectBox is all about sticking objects in boxes, you interact with objects using aBoxinterface. For each object class, there is a matching Box instance.

To manage your entities, you retrieve the ObjectBox.Box<T> instance for its class from yourStore. Boxes are lightweight and can be discarded, but then you have to pass the Store around. You will almost always prefer to pass long-lived Box instances around instead, for example in segues between UIViewControllers.

let exampleEntityBox = store.box(for: ExampleEntity.self)
// Similarly:
let personBox = store.box(for: Person.self)
let noteBox: Box<Note> = store.box()

Wherever you have access to a Box, you can use it to persist objects and fetch objects from disk. Boxes are thread safe. Here are some of the basic operations:

• put: Persist an object, which may overwrite an existing object with the same ID. In other words, use putto insert or update objects. When put succeeds, an ID will be assigned to the entity. There are put variants that support writing multiple objects at once, which is more efficient than writing each with its own call to put.

• get: When you have an object's ID, you can get to the object very efficiently using get. To get all objects of a type, use all.

• remove: Deletes a previously persisted object from its box. There are method overloads to remove multiple entities, and removeAll to delete all objects and empty the box.

• count: The number of objects stored in this box.

• query: Lets you provide a query expression to retrieve objects by certain criteria. See the page on queries for details.

Check the API docs for Box for a list of operations.

Put and Get Example

Once you have a box, it is simple to persist an entity. To illustrate the change of IDs, we added assertions to the code; you don't need these, of course.

// let's start with an empty box
assert(try exampleEntityBox.isEmpty())

let exampleEntity = ExampleEntity()
assert(exampleEntity.id.value == 0)

let newID = try exampleEntityBox.put(exampleEntity)
// Change of ID with the `put`:
assert(exampleEntity.id.value != 0)
assert(exampleEntity.id == newID)

// Check the Box contents did indeed change:
assert(try exampleEntityBox.count() == 1)
assert(try exampleEntityBox.all().first?.id == newID)

// Getting to a specific object
guard let foundEntity = try exampleEntityBox.get(newID) 
    else { fatalError("Object should be in the box") }
assert(exampleEntity.id == foundEntity.id)

// Cleaning up
try exampleEntityBox.removeAll()
assert(try exampleEntityBox.count() == 0)

Put with structs

Structs basically work the same way as classes. However, since structs are value types, ObjectBox can only adjust their ID if you pass them by reference. So if you have a mutable struct, remember to pass it by reference:

// objectbox: entity
struct Author {
    var id: Id // Do not initialize the ID to 0 for structs.
    var name: String
    var age: Int
}

let exampleEntityBox = store.box(for: Author.self)
var exampleEntity = Author(id: 0, name: "Nnedi Okorafor", age: 45)

// Put the struct and update the ID:
try exampleEntityBox.put(&exampleEntity)
assert(exampleEntity.id != 0)

Alternately, you can manually update the struct's ID field by using putAndReturnID() or putAndReturnIDs() to get the ID a struct was written as:

exampleEntity.id = exampleEntityBox.putAndReturnID(exampleEntity)

Given immutable structs are such a common occurrence, ObjectBox generates a convenience method for you to help with updating the ID on an immutable struct, put(struct:), which will automatically create a new copy of your struct with the ID filled out:

// objectbox: entity
struct Author {
    let id: Id // Do not initialize the ID to 0 for structs.
    let name: String
    let age: Int
}

// Let's start with an empty box:
let exampleEntityBox = store.box(for: Author.self)
let exampleEntity = Author(id: 0, name: "Nnedi Okorafor", age: 45)

// Put the immutable struct:
let newEntity = try exampleEntityBox.put(struct: exampleEntity)
assert(newEntity.id != 0)

Note that, after writing exampleEntity, you must use newEntity from then on. If you called put(struct:) or put() on exampleEntity again, ObjectBox would not know that this object has already been saved, and would write a second copy of it to the database.

But what if you know you already saved an immutable entity, and you already made a copy because you changed one of its fields, and don't need another copy? Then you can call put(), just like above:

// Modify object:
let futureExampleEntity = Author(id: newEntity.id, name: newEntity:name,
                                        age: newEntity.age + 1)

// Write out changes:
try exampleEntityBox.put(futureExampleEntity)

So beyond having to use a special call the first time you write out an entity, everything is the same as with classes.

For ObjectBox to work with structs, there needs to be an init() method on your struct that accepts all its persisted properties. In the above example, the default initializer provided for the struct by Swift does just fine, but if you have properties that are not persisted, or you are defining your own initializer, you may also have to provide that initializer.

Note that for structs you will usually not want to specify a default value of 0 for the ID like you do for classes. If you do, the default initializer will omit the "id:" parameter and there would be no way to initialize the ID without writing your own initializer.

Transactions

Transactions in ObjectBox let you group together several operations and ensure that either all of them complete, or none does, always leaving your data relations in a consistent state. If you do not run your own transaction, ObjectBox will implicitly create one for every call:

• A put runs an implicit transaction.

• Prefer the put variant that takes an array of entities (like put([person1, person2])) whenever possible to increase performance.

For a high number of interactions inside loops, consider wrapping the loop in explicit transactions. Store exposes methods like runInTransaction for this purpose.

// Bad/slow, each Put runs inside a new transaction
for i in (1...1000) {
    try box.put(AnEntity(number: i))
}

// Possible, but still inefficient
try store.runInTransaction {
    for i in (1...1000) {
        try box.put(AnEntity(number: i))
    }
}

// Much better
let allEntities: [AnEntity] = (1...1000).map(AnEntity.init(number:))
try box.put(allEntities)

For details, check the Transaction guide and the API docs for Store for details.