Implement AlbumSerializer in music app and update docs

Expanded the existing service of the music app by introducing the AlbumSerializer. This includes defining required fields, and creating methods for 'create' and 'update' operations. The documentation is correspondingly updated to explain the new AlbumSerializer and its methods.

Author: lipemorais

docs/images/index.md

@@ -464,6 +464,54 @@ Last but not least `destroy` action to delete albums
 
 With `destroy` set the we finish the change on `music.views.py`
 
+Now we go for our `AlbumSerializer`
+
+```python
+class AlbumSerializer(serializers.Serializer):
+    title = serializers.CharField()
+    artist = ArtistSerializer()  # Serializers inherits from Field, so it can be used as fields too
+    release_year = serializers.IntegerField()
+
+    class Meta:
+        fields = ['title', 'artist', 'release_year']
+```
+
+1. First we define our `AlbumSerializer` inheriting from `serializers.Serializer`
+2. With the fields `title`, `artist`, `release_year` with it respective fields
+3. We also need to list the fields inside the class Meta
+
+Additionally we need to add 2 methods to let DRF know how to save and how to update the Albums.
+
+The first is `create`
+
+```python
+    def create(self, validated_data):
+        artist_data = validated_data.pop('artist')
+        artist, created = Artist.objects.get_or_create(name=artist_data['name'])
+        return Album.objects.create(artist=artist, **validated_data)
+```
+1. Where we create the album but since the album has artist as a nested model we need to create it here before try to save the album itself.
+2. Don't forget to import the `Album` model here with `from music.models import Album`
+
+and the `update` method
+```python
+    def update(self, album, validated_data):
+        artist_data = validated_data.pop('artist')
+        artist, created = Artist.objects.get_or_create(name=artist_data['name'])
+
+        album.title = validated_data.get('title', album.title)
+        album.release_year = validated_data.get('release_year', album.release_year)
+        album.artist = artist
+        album.save()
+
+        return album
+```
+1. To update we need to do the same with the `Artist` model, creating/getting it before save the Album
+2. So we get the new fields and save it
+3. Last we return the updated album
+
+With everything set we can see it working live.
+
 ## Bonus content
 
 ### Serializers deep dive

first_api/music/serializers.py

@@ -1,9 +1,37 @@
 from rest_framework import serializers
 
-from music.models import Artist
+from music.models import Artist, Album
 
 
 class ArtistSerializer(serializers.HyperlinkedModelSerializer):
     class Meta:
         model = Artist
         fields = ['name']
+
+
+# You could use the HyperlinkedModelSerializer here but
+# want you to know how a plain serializer works
+# class AlbumSerializer(serializers.HyperlinkedModelSerializer):
+class AlbumSerializer(serializers.Serializer):
+    title = serializers.CharField()
+    artist = ArtistSerializer()  # Serializers inherits from Field, so it can be used as fields too
+    release_year = serializers.IntegerField()
+
+    class Meta:
+        fields = ['title', 'artist', 'release_year']
+
+    def create(self, validated_data):
+        artist_data = validated_data.pop('artist')
+        artist, created = Artist.objects.get_or_create(name=artist_data['name'])
+        return Album.objects.create(artist=artist, **validated_data)
+
+    def update(self, album, validated_data):
+        artist_data = validated_data.pop('artist')
+        artist, created = Artist.objects.get_or_create(name=artist_data['name'])
+
+        album.title = validated_data.get('title', album.title)
+        album.release_year = validated_data.get('release_year', album.release_year)
+        album.artist = artist
+        album.save()
+
+        return album