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() {
        // 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.

Ways to Define IDs

To specify Entity IDs, you need to have a property of type Id . The code generator will look for one of these configurations, in the following order

1. A property that has a // objectbox: id comment annotation on the line above the property definition.

2. A property named var id: Id.

3. Any other property of the Id type, if there is only one.

You usually don't need more than one property of the Id type. Use ObjectBox's support for object relations if you need to connect entities with each other. In any case, should you need to store a reference to another object for an unusual purpose, simply use annotations to ensure ObjectBox uses the right property as the entity's ID.

Here's an example of using annotations in action:

// objectbox: entity
class ExampleEntity {
    var anotherID: Id = 0
​
    // objectbox: id
    var theEntityIdentifier: Id = 0 // <- this will be used
    
    required init() {
        // nothing to do here
    }
}

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/")

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(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(exampleEntityBox.count() == 1)
assert(exampleEntityBox.all().first?.id == newID)
​
// Getting to a specific object
guard let foundEntity = exampleEntityBox.get(newID) 
    else { fatalError("Object should be in the box") }
assert(exampleEntity.id == foundEntity.id)
​
// Cleaning up
try exampleEntityBox.removeAll()
assert(exampleEntityBox.count() == 0)

Put with structs

Structs basically work the same way as classes. However, since structs are often immutable, ObjectBox doesn't adjust their ID. So if you have a mutable struct, remember to update its ID after you put() it:

// 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)
let exampleEntity = Author(id: 0, name: "Nnedi Okorafor", age: 45)
​
// Put the struct and update the ID:
exampleEntity.id = try exampleEntityBox.put(exampleEntity)
assert(exampleEntity.id != 0)

Given immutable structs are such a common occurrence, ObjectBox generates a convenience method for you to help with updating the ID, 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 using a different call and the initial speed-bump of having to update the ID yourself the first time you write out an entity, everything is the same as with classes.

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
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.