finish fields docs intial ver,add test for related name, fix child_name(s) in reverse relations

docs_src/fields/docs003.py

@@ -0,0 +1,41 @@
+import orm
+import databases
+import sqlalchemy
+
+database = databases.Database("sqlite:///db.sqlite")
+metadata = sqlalchemy.MetaData()
+
+
+class Album(orm.Model):
+    __tablename__ = "album"
+    __metadata__ = metadata
+    __database__ = database
+
+    id = orm.Integer(primary_key=True)
+    name = orm.String(length=100)
+
+
+class Track(orm.Model):
+    __tablename__ = "track"
+    __metadata__ = metadata
+    __database__ = database
+
+    id = orm.Integer(primary_key=True)
+    album = orm.ForeignKey(Album, nullable=False)
+    title = orm.String(length=100)
+    position = orm.Integer()
+
+
+album = await Album.objects.create(name="Brooklyn")
+await Track.objects.create(album=album, title="The Bird", position=1)
+
+# explicit preload of related Album Model
+track = await Track.objects.select_related("album").get(title="The Bird")
+assert track.album.name == 'Brooklyn'
+# Will produce: True
+
+# even without explicit select_related if ForeignKey is not nullable,
+# the Album Model is still preloaded.
+track2 = await Track.objects.get(title="The Bird")
+assert track2.album.name == 'Brooklyn'
+# Will produce: True