Live Objects with Realm

Value Objects are preached by followers of the functional reactive programming paradigm in the mobile development community. They are neat, but Live Objects have their own advantages as well. They always reflect the latest modifications across threads and processes. This talk reminds of those and explains how they give a whole new experience when working with persistency as given by the Realm database. Beside a general introduction in both concepts and their differentiation, you can expect a technical deep dive in how the Realm Cocoa bindings are implementing them.

Transcript

1. Live Objects with Realm 1
4. What is this? Some Sort of Buzzword? 4
5. Let me answer that by answering: What They Are Not? 5
6. (Immutable | Value) Objects 6
7. These are neat: 4 Simple 4 Automatically Thread-Safe 7
8. But: 4 Expensive 4 Limitations 4 Modifications of Large Trees can be Cumbersome!* 8
9. Swift struct InventoryItem { var name: String var quantity: Int = 1 var category: Category } 9
10. 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
11. - (InventoryItem *)itemWithName:(NSString *)name { return [Item itemWithName:name quantity:self.quantity category:self.category]; } 11
12. 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
13. How to Interact with These? e.g. Retrieve an InventoryItem from a database, modify the quantity, persist the change in the database. 13
14. 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
15. Modify InventoryItem modifiedItem = InventoryItem(item.name, quantity+1, item.category); 15
16. 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
17. Underlying Principle Push To & Pull From the Database 17
18. You can Limit State and Side-Effects in your Application But it is still there … 18
19. The Alternative: Embrace State 19
20. Live Objects 4 Fundamentally Different 4 Always Represent the Latest State 4 Navigatable 4 But Not Necessarily Thread-Safe 20
21. Example import RealmSwift class InventoryItem : Object { dynamic var name: String dynamic var quantity: Int = 1 dynamic var category: Category? } 21
22. Retrieve, Persist, Modify let results = realm.objects(InventoryItem) .filter("name = %@", "Drilling machine") let obj = results.first! realm.write { obj.quantity += 1 } 22
23. How does that work? 23
24. ! Objects store a reference to their row under the hood. They always carry identity. 24
25. ! Properties are dynamically implemented at runtime. 25
26. !→ " !"#→ ✅ Modifications are only allowed within write transactions and directly occur on the database. 26
27. !" MVCC algorithm keeps all versions around that are necessary. 27
28. MVCC? 28
29. Multi-Version- Concurrency-Control 29
33. ! On every commit all accessors are updated across threads and processes. 33
34. ! Change Notifications are sent. Per Object / Collection (taking applied filters into account!) 34
35. ! MVCC algorithm disposes old commits which are not necessary anymore. 35
36. Does this mean the whole data is copied every time? 36
37. ! Not necessary by Copy-on-Write 37
38. !"# The Birds and The B-Trees 38
39. What are my Advantages? 39
40. 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
41. Demo 41
42. for question in questions { question.ask()! } 42
43. Thanks for your attention! @mrackwitz mr@realm.io 43