Live Objects with Realm 1 

2 

3 

What is this? Some Sort of Buzzword? 4 

Let me answer that by answering: What They Are Not? 5 

(Immutable | Value) Objects 6 

These are neat: 4 Simple 4 Automatically Thread-Safe 7 

But: 4 Expensive 4 Limitations 4 Modifications of Large Trees can be Cumbersome!* 8 

Swift struct InventoryItem { var name: String var quantity: Int = 1 var category: Category } 9 

Objective-C @interface InventoryItem : NSObject @property (nonatomic, copy) NSString *name; @property (nonatomic, assign) NSInteger quantity; @property (nonatomic, strong) Category *category; - (instancetype)itemWithName:(NSString *)name quantity:(NSInteger)quantity category:(Category *)category; @end 10 

- (InventoryItem *)itemWithName:(NSString *)name { return [Item itemWithName:name quantity:self.quantity category:self.category]; } 11 

Java public final class InventoryItem { private final String name; private final Int quantity; private final Category category; public InventoryItem(String name, Int quantity, Category category) { this.name = name; this.quantity = quantity; this.category = category; } public String getName() { return name; } public Int getQuantity() { return quantity; } public Category getCategory() { return category; } } 12 

How to Interact with These? e.g. Retrieve an InventoryItem from a database, modify the quantity, persist the change in the database. 13 

Retrieve Cursor c = db.query("inventory_items", { "name", "quantity", "categoryId" }, "name = ?", { "Drilling machine" }, null, null, null, 1); c.moveToFirst(); String name = c.getString(c.getColumnIndexOrThrow("name")); Int quantity = c.getInt(c.getColumnIndexOrThrow("quantity")); Long categoryId = c.getLong(c.getColumnIndexOrThrow("categoryId")); Category category = getCategoryById(categoryId); InventoryItem item = InventoryItem(name, quantity, category); 14 

Modify InventoryItem modifiedItem = InventoryItem(item.name, quantity+1, item.category); 15 

Persist // New value for one column ContentValues values = new ContentValues(); values.put("name", modifiedItem.name); values.put("categoryId", modifiedItem.category.id); values.put("quantity", modifiedItem.quantity); int count = db.update( "inventory_items", values, "name = ?", { item.name }); 16 

Underlying Principle Push To & Pull From the Database 17 

You can Limit State and Side-Effects in your Application But it is still there … 18 

The Alternative: Embrace State 19 

Live Objects 4 Fundamentally Different 4 Always Represent the Latest State 4 Navigatable 4 But Not Necessarily Thread-Safe 20 

Example import RealmSwift class InventoryItem : Object { dynamic var name: String dynamic var quantity: Int = 1 dynamic var category: Category? } 21 

Retrieve, Persist, Modify let results = realm.objects(InventoryItem) .filter("name = %@", "Drilling machine") let obj = results.first! realm.write { obj.quantity += 1 } 22 

How does that work? 23 

! Objects store a reference to their row under the hood. They always carry identity. 24 

! Properties are dynamically implemented at runtime. 25 

!→ " !"#→ ✅ Modifications are only allowed within write transactions and directly occur on the database. 26 

!" MVCC algorithm keeps all versions around that are necessary. 27 

MVCC? 28 

Multi-Version- Concurrency-Control 29 

30 

31 

32 

! On every commit all accessors are updated across threads and processes. 33 

! Change Notifications are sent. Per Object / Collection (taking applied filters into account!) 34 

! MVCC algorithm disposes old commits which are not necessary anymore. 35 

Does this mean the whole data is copied every time? 36 

! Not necessary by Copy-on-Write 37 

!"# The Birds and The B-Trees 38 

What are my Advantages? 39 

Advantages of Realm's Live Objects Concept 4 Single source of truth for your model schema 4 No overhead of mapping data around 4 Change notifications for free 40 

Demo 41 

for question in questions { question.ask()! } 42 

Thanks for your attention! @mrackwitz [email protected] 43