Realm Model Classes

A tale about overcoming the limitations
of the annotation processor

Transcript

1. REALM MODEL CLASSES A tale about overcoming the limitations of the annotation processor Emanuele Zattin - Realm @emanuelez 10-08-2016 - DroidDevs CPH
3. > Fast, zero-copy, embedded database > Installed on 1 Billion+ devices > Trusted by tens of thousands of devs > Object & model-oriented > Full ACID transactions > Well defined threading model > Cross-platform C++ core with language bindings
4. REALM MODEL CLASSES Up to a few months ago Realm was imposing several limitations on how model classes were defined They were POJOs, but not quite, so let's see why
5. RULES ON THE NAME OF GETTERS AND SETTERS
6. Getters had to be called: > get<FieldName>() > is<FieldName>() was allowed for boolean fields Setters had to be called: > set<FieldName>()
7. This limitation usually went unnoticed because the accessors generated by Android Studio follow such rules already!
8. WHY?
9. The Java Annotation Processing API does not allow to introspect how methods are implemented. This means that Realm had to "guess" which methods were accessors for which fields.
10. LOGIC IN ACCESSORS
11. Wanted to validate user input? public void setName(String name) { if (name == null) { // handle the case } this.name = name; }
12. Wanted to convert or decorate data? public String getName() { return "Mr. " + name; }
13. This was only possible using utility static methods. public static boolean isValidName(String name) { return name != null; } public static String getTitledName(Person person) { return "Mr. " + person.getName(); }
14. WHY?
15. Realm generates proxy classes for your model classes. > Person ⟶ PersonRealmProxy Because of the reason mentioned before Realm cannot replicate your logic in the proxied accessors. This will of course work fine for standalone objects.
16. NO CUSTOM METHODS ALLOWED
17. It was not possible to have a method such as this one: public String getFullName() { return this.lastName + " " + this.firstName; }
18. Once again the workaround consisted on static utility methods: public static String getFullName(Person person) { return person.getLastName() + " " + person.getFirstName(); }
19. WHY?
20. In theory this could be possible if we stated the rule that, in such methods, fields can only be accessed with accessors, but such rule would have been hard to enforce and easy to forget, causing many subtle bugs so we decided to disallow it.
21. NO INTERFACE IMPLEMENTATION ALLOWED
22. On Realm model classes you could not do this: public class Person extends RealmObject implements Parcelable { // ← ☹ // fields and accessors }
23. WHY?
24. This was of course a consequence of the lack of support for custom methods.
25. NO CUSTOM toString() equals() hashCode()
26. Again, this was not possible. public class Person extends RealmObject { private String firstName; private int age; // getters & setters public void toString() { return firstName + " is " + age + " years old" } }
27. WHY?
28. Again, we could allow this, but decided not to because the misuse would be too easy and provoke subtle bugs
29. THIS WAS SIMPLY NOT GOOD ENOUGH!
30. THE PROBLEM: ANNOTATION PROCESSING IS NOT POWERFUL ENOUGH
31. THE SOLUTION
32. BYTECODE WEAVING
33. For months we have been working on a project. Internally it was called Better Objects
34. WHAT DOES IT CONSIST OF? Use the Transform API to: > add custom accessors to model classes > replace field access with accessors The custom accessors are called: > realmGet$<fieldName> > realmSet$<fieldName>
35. Public fields? No problem! public class Person extends RealmObject { public String name; public int age; }
36. Accessors with custom names public class Person extends RealmObject { private String name; public String thisIsMyNameGetter() { return this.name; } }
37. Accessors with custom logic public class Person extends RealmObject { private String name; public void setName(String name) { if (name == null || name.equals("")) { throw new GreatExceptionOfDoom(); } this.name = name; } }
38. Custom methods public class Person extends RealmObject { public String firstName; public int lastName; public String getFullName() { return this.firstName + " " + this.lastName; } }
39. Implement interfaces public class Person extends RealmObject implements Parcelable { private String name; private int age; // Tedious Parcelable API methods here }
40. Custom Object methods public class Person extends RealmObject { public String name; public int age; public String toString() { return this.name + " is " + this.age + " years old"; } }
41. !
42. This has been introduced in 0.88.0 (March 10)
43. BUT WAIT, THERE'S MORE!
44. RealmObject
45. Some people just did not like having to extend a base class
46. A new way! @RealmClass public class User implements RealmModel { // ... }
47. This has been introduced in 0.90.0 (April 21)
48. WE ARE HIRING! https://jobs.lever.co/realm
49. THANK YOU!