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REALM MODEL CLASSES
THE PAST, PRESENT AND FUTURE
Emanuele Zattin - Realm
@emanuelez
20-02-2016 - Realm Meetup Tokyo
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REALM MODEL CLASSES
At the current stage Realm is imposing several limitations
on how model classes are defined
They are POJOs, but not quite, so let's see why
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RULES ON THE NAME OF
GETTERS AND SETTERS
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Getters must me called:
> get()
> is() is allowed for boolean fields
Setters must be called:
> set()
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This limitation usually goes unnoticed because the
accessors generated by Android Studio follow such rules
already!
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WHY?
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The Java Annotation Processing API does not allow to
introspect how methods are implemented.
This means that right now Realm has to "guess" which
methods are accessors for which fields.
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ACCESSORS CANNOT
CONTAIN ANY LOGIC
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Want to validate user input?
public void setName(String name) {
if (name == null) {
// handle the case
}
this.name = name;
}
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Want to convert or decorate data?
public String getName() {
return "Mr. " + name;
}
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Right now this is 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();
}
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WHY?
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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.
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NO CUSTOM METHODS
ALLOWED
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Right now it's not possible to have a method such as this
one:
public String getFullName() {
return this.lastName + " " + this.firstName;
}
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Once again the current workaround consists on static
utility methods:
public static String getFullName(Person person) {
return person.getLastName() + " " + person.getFirstName();
}
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WHY?
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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 be hard to enforce and
easy to forget, causing many subtle bugs so we decided
to disallow it.
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NO INTERFACE
IMPLEMENTATION
ALLOWED
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Currently on Realm model classes you cannot do this:
public class Person
extends RealmObject
implements Parcelable { // ← ☹
// fields and accessors
}
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WHY?
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This is of course a consequence of the lack of support
for custom methods.
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NO CUSTOM
toString()
equals()
hashCode()
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Again, this is currently not possible.
public class Person extends RealmObject {
private String firstName;
private int age;
// getters & setters
public void toString() {
return firstName + " is " + age + " years old"
}
}
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WHY?
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Again, we could allow this, but decided not to because
the misuse would be too easy and provoke subtle bugs
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THIS IS NOT GOOD
ENOUGH!
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THE PROBLEM:
ANNOTATION
PROCESSING IS NOT
POWERFUL ENOUGH
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THE SOLUTION
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BYTECODE WEAVING
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In the past few months we have been working on a
project.
Internally it's being called Better Objects
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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$
> realmSet$
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Public fields? No problem!
public class Person extends RealmObject {
public String name;
public int age;
}
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Accessors with custom names
public class Person extends RealmObject {
private String name;
public String thisIsMyNameGetter() {
return this.name;
}
}
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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;
}
}
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Custom methods
public class Person extends RealmObject {
public String firstName;
public int lastName;
public String getFullName() {
return this.firstName + " " + this.lastName;
}
}
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Implement interfaces
public class Person extends RealmObject implements Parcelable {
private String name;
private int age;
// Tedious Parcelable API methods here
}
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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";
}
}
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!
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WHEN???
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Currently in the last stages of review.
Soon to be merged to master and made available as
SNAPSHOT
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THE FUTURE
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ͫΞ͜Ο
RealmObject?
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Currently being discussed as Github issue 2296
github.com/realm/realm-java/pull/2296
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THANK YOU!