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

docs_src/fields/docs001.py

@@ -0,0 +1,36 @@
+import databases
+import sqlalchemy
+
+import orm
+
+database = databases.Database("sqlite:///db.sqlite")
+metadata = sqlalchemy.MetaData()
+
+
+class Department(orm.Model):
+    __database__ = database
+    __metadata__ = metadata
+
+    id = orm.Integer(primary_key=True)
+    name = orm.String(length=100)
+
+
+class Course(orm.Model):
+    __database__ = database
+    __metadata__ = metadata
+
+    id = orm.Integer(primary_key=True)
+    name = orm.String(length=100)
+    completed = orm.Boolean(default=False)
+    department = orm.ForeignKey(Department)
+
+
+department = Department(name='Science')
+course = Course(name='Math', completed=False, department=department)
+
+print(department.courses[0])
+# Will produce:
+# Course(id=None,
+#        name='Math',
+#        completed=False,
+#        department=Department(id=None, name='Science'))

docs_src/fields/docs002.py

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+import databases
+import sqlalchemy
+
+import orm
+
+database = databases.Database("sqlite:///db.sqlite")
+metadata = sqlalchemy.MetaData()
+
+
+class Department(orm.Model):
+    __database__ = database
+    __metadata__ = metadata
+
+    id = orm.Integer(primary_key=True)
+    name = orm.String(length=100)
+
+
+class Course(orm.Model):
+    __database__ = database
+    __metadata__ = metadata
+
+    id = orm.Integer(primary_key=True)
+    name = orm.String(length=100)
+    completed = orm.Boolean(default=False)
+    department = orm.ForeignKey(Department, related_name="my_courses")
+
+department = Department(name='Science')
+course = Course(name='Math', completed=False, department=department)
+
+print(department.my_courses[0])
+# Will produce:
+# Course(id=None,
+#        name='Math',
+#        completed=False,
+#        department=Department(id=None, name='Science'))
+

docs_src/fields/docs003.py

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+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