AutoValue: Firebase Extension

For value classes to be compatible with Firebase Realtime Database, they must:

• contain public "get"-prefixed accessors or public fields, and
• contain an empty, or "default," constructor.

If we want to use AutoValue, the first requirement is achievable -- we can prefix getters with "get" -- though many among us may prefer to name our getters without the "get" prefix.

The second requirement is impossible -- AutoValue simply doesn't generate default constructors.

This library is an AutoValue extension for generating Firebase Realtime Database compatible value classes with easy conversions between your AutoValue and FirebaseValue instances.

Usage

Just add auto-value-firebase to your project and add the @FirebaseValue annotation to your existing @AutoValue annotated classes.

This extension creates Firebase Realtime Database compatible static inner classes, each named FirebaseValue, inside your generated AutoValue classes. From there, it's easy to convert your AutoValue object to a FirebaseValue object.

Example

Here's a simple AutoValue class called Taco:

@AutoValue
public abstract class Taco {

  public static Taco create(String name, List<Ingredient> ingredients, Review review) {
    return new AutoValue_Taco(name, ingredients, review);
  }

  public abstract String name();

  public abstract List<Ingredient> ingredients();

  public abstract Review review();
}

From here, we just add the @FirebaseValue annotation. This generates our FirebaseValue class as a static inner class of AutoValue_Taco.

@AutoValue @FirebaseValue
public abstract class Taco {

  public static Taco create(String name, List<Ingredient> ingredients, Review review) {
    return new AutoValue_Taco(name, ingredients, review);
  }

  public static Taco create(DataSnapshot dataSnapshot) {
    return dataSnapshot.getValue(AutoValue_Taco.FirebaseValue.class).toAutoValue();
  }

  public Object toFirebaseValue() {
    return new AutoValue_Taco.FirebaseValue(this);
  }

  public abstract String name();

  public abstract List<Ingredient> ingredients();

  public abstract Review review();
}

In addition to the empty constructor required by Firebase Realtime Database, the generated FirebaseValue class includes a constructor that takes your AutoValue class as an argument. The generated FirebaseValue class also includes a toAutoValue() method to convert it back to the AutoValue instance.

The create(DataSnapshot) and toFirebaseValue methods aren't required, but this is how I'd recommend converting your AutoValue objects to and from their corresponding FirebaseValue objects.

Collections

The generated FirebaseValue class has a toMap() method that can be used for DatabaseReference's updateChildren(Map<String, Object>) method.

For example, you could add the following method to the Taco class above:

public Map<String, Object> toMap() {
  return new AutoValue_Taco.FirebaseValue(this).toMap();
}

Additionally, if you want to deserialize a collection of objects directly from a DataSnapshot, you could just iterate through its children and convert each object from FirebaseValue to AutoValue. This method could be added to the Taco class above.

public static Map<String, Taco> createMap(DataSnapshot snapshot) {
  Map<String, Taco> tacos = new HashMap<>();
  for (DataSnapshot child : snapshot.getChildren()) {
    tacos.put(child.getKey(), child.getValue(AutoValue_Taco.FirebaseValue.class).toAutoValue());
  }
  return tacos;
}

TypeAdapters

Type adapters can be declared and used as follows:

public class DateAdapter implements TypeAdapter<Date, Long> {
  @Override
  public Date fromFirebaseValue(Long value) {
    return new Date(value);
  }

  @Override
  public Long toFirebaseValue(Date value) {
    return value.getTime();
  }
}

@AutoValue @FirebaseValue
public abstract class Review {

  public static Review create(String description, int rating, Date reviewDate) {
    return new AutoValue_Review(description, rating, reviewDate);
  }

  public abstract String description();

  public abstract int rating();

  @FirebaseAdapter(DateAdapter.class) public abstract Date dateOfReview();
}

Supported types

This extension can generate FirebaseValue classes that contain any types that Firebase Realtime Database supports as described in their documentation except for nested collections.

For example, List<Ingredient> is supported but List<List<Ingredient>> is not. This might come in a later release.

Firebase annotations

Firebase Realtime Database provides four annotations to configure the mapping from your value classes to the cloud database and back. You can annotate your methods with @Exclude or @PropertyName, and you can annotate your classes with @IgnoreExtraProperties or @ThrowOnExtraProperties.

If you want these annotations to be included in your generated FirebaseValue class, just add them to your abstract AutoValue class.

Naming

This extension uses the method names from your AutoValue class to generate the fields and getters on the generated FirebaseValue class.

As a result, it's required that you don't prefix your getters with get.

Download

This extension should be included as an apt dependency (if you're using android-apt).

The @FirebaseValue annotation is packaged separately, and should be included as a provided dependency.

Type adapter support is optional and can be included as a compile dependency.

apt 'me.mattlogan.auto.value:auto-value-firebase:1.1.0'
provided 'me.mattlogan.auto.value:auto-value-firebase-annotation:1.1.0'

// Optional type adapter dependency
compile 'me.mattlogan.auto.value:auto-value-firebase-adapter:1.1.0'

License

Copyright 2017 Matt Logan

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.