Documentation versions

Persistence

For those programmers who have an object oriented model (which is recommended, but not strictly necessary to use Reahl), we provide glue to the object relational mapping tools provided by SqlAlchemy.

Reahl allows you to build and distribute parts of your program as reusable components. Existing tools for the task of migrating an existing database to a newer schema do not take our components into account. Hence, Reahl adds some additional infrastructure to help with database migration. (See the tutorial for more on this topic.)

Here is an example showing the use of SqlAlchemy. Reahl merely provides versions of SqlAlchemy’s Session, Base and metadata objects for use with Reahl applications. Further use is just normal SqlAlchemy.

Our example first comes up with only a (somewhat prettied up) form asking the user to leave a comment:

A screenshot of a form with input for a user's email.

When the user clicks on submit, the new comment is persisted in the database. When the page is refreshed, the form is still rendered, but a list of all the comments in the database is shown below it:

A screenshot of a form with input for a user's email, and also a list of previously entered email addresses.

Read the complete example source code:

from __future__ import print_function, unicode_literals, absolute_import, division

from sqlalchemy import Column, UnicodeText, Integer
from reahl.sqlalchemysupport import Session, Base

from reahl.web.fw import UserInterface
from reahl.web.ui import Button, Form, InputGroup, LabelledBlockInput
from reahl.web.ui import HTML5Page, P, Panel, TextInput
from reahl.component.modelinterface import exposed, EmailField, Field
from reahl.component.modelinterface import Event, Action


class PersistenceUI(UserInterface):
    def assemble(self):
        self.define_view('/', title='Persistence demo', page=HomePage.factory())


class HomePage(HTML5Page):
    def __init__(self, view):
        super(HomePage, self).__init__(view, style='basic')

        self.body.add_child(CommentForm(view))

        for comment in Session.query(Comment).all():
            self.body.add_child(CommentBox(view, comment))


class Comment(Base):
    __tablename__ = 'features_comment'
    
    id = Column(Integer, primary_key=True)
    email_address = Column(UnicodeText)
    text          = Column(UnicodeText)
    
    @exposed
    def fields(self, fields):
        fields.email_address = EmailField(label='Email address', required=True)
        fields.text          = Field(label='Comment', required=True)

    @exposed
    def events(self, events):
        events.submit = Event(label='Submit', action=Action(self.submit))

    def submit(self):
        Session.add(self)


class CommentForm(Form):
    def __init__(self, view):
        super(CommentForm, self).__init__(view, 'myform')

        new_comment = Comment()
        grouped_inputs = InputGroup(view, label_text='Leave a comment')
        self.add_child(grouped_inputs)

        email_input = TextInput(self, new_comment.fields.email_address)
        grouped_inputs.add_child( LabelledBlockInput(email_input) )

        text_input = TextInput(self, new_comment.fields.text)
        grouped_inputs.add_child( LabelledBlockInput(text_input) )

        self.define_event_handler(new_comment.events.submit)
        grouped_inputs.add_child( Button(self, new_comment.events.submit) )


class CommentBox(Panel):
    def __init__(self, view, comment):
        super(CommentBox, self).__init__(view)
        comment_text = 'By %s: %s' % (comment.email_address, comment.text)
        self.add_child(P(view, text=comment_text))
        

Previous topic

Reacting to user events

Next topic

Access control example

Documentation versions