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auto-value-firebase

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AutoValue extension for creating Firebase Realtime Database objects

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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`:

```java
@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`.

```java
@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:
 
```java
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.

```java
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:
```java
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();
  }
}
```

```java
@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.

```groovy
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
-------

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.

[AutoValue]: https://github.com/google/auto/tree/master/value
 [Firebase Realtime Database]: https://firebase.google.com/docs/database/
 [android-apt]: https://bitbucket.org/hvisser/android-apt
 [documentation]: https://firebase.google.com/docs/database/android/save-data

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