introduce docs -> models section mostly finished

docs_src/models/docs006.py

@@ -0,0 +1,41 @@
+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('name' in course.__dict__)
+# False <- property name is not stored on Course instance
+print(course.name)
+# Math <- value returned from underlying pydantic model
+print('department' in course.__dict__)
+# False <- related model is not stored on Course instance
+print(course.department)
+# Department(id=None, name='Science') <- Department model
+# returned from RelationshipManager
+print(course.department.name)
+# Science