To understand the Display class, let us create a very simple application. Type in the following code and run it:
Chapter8/crmcontact.py
import os
import cherrypy
from entity import AbstractEntity, Attribute, Picklist
from browse import Browse
from display import Display
from logondb import LogonDB
db="/tmp/crmcontact.db"
class Entity(AbstractEntity):
database = db
class Contact(Entity):
firstname = Attribute(displayname="First Name")
lastname = Attribute(displayname="Last Name",
notnull=True,
primary=True)
gender = Attribute(displayname="Gender",
notnull=True,
validate=Picklist(
Male=1,Female=2,Unknown=0))
telephone = Attribute(displayname="Telephone")
class ContactBrowser(Browse):
edit = Display(Contact, edit=True)
add = Display(Contact, add=True)
current_dir = os.path.dirname(os.path.abspath(__file__))
cherrypy.quickstart(ContactBrowser(Contact),config={
'/':
{ 'log.access_file' :
os.path.join(current_dir,"access.log"),
'log.screen': False,
'tools.sessions.on': True
}
})
When you point your browser to http://localhost:8080, you will be presented with an empty list of contacts that you may expand by clicking the Add button. This will present you with the following screen:
Here you may enter new values, and when you click the add button, a new contact will be added to the database, after which, you will return to the list of contacts, but now with an extra one added.
In the application tree that we constructed, we mounted several instances of the Display class, each with its own initialization parameters. These parameters are merely stored in the instance by the __init__() method for referral later:
Chapter8/display.py
def __init__(self, entity, edit=False, add=False, logon=None, columns=None): self.entity = entity self.edit = edit self.add = add self.logon = logon if columns is None: self.columns = entity.columns else: self.columns = columns
The most important parameter is entity. This will be the Entity class that we want Display to be able to add or edit.
__init__() also takes an edit or add parameter that when set will determine the type of activity this instance of Display will perform. If neither is given, an instance will just be displayed without the possibility of altering its attributes. In the stripped down crmcontact.py application, we created a ContactBrowser class that holds references to two different instances of the Display class. The one in the add class variable is created with an add attribute set to True, while the one in the edit variable is created with an edit attribute set to True. The Add new button in the browser is equipped with a click handler that will replace the browse list with the form that will be served by the Display instance that was created with the add argument.