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3.7.
Permissions Roles and Definitions
3.8. How to do add validation to Forms
Validate Input
To avoid user errors validations must be carried out and a feedback to the user is required indicating the error/requirement.
How to write Validators
Required Validators
Common requirements for validation in Bungeni are:
Validate field against db-constraints
Required Field
A required fields must contain a value.
This is normally handled at database schema level:
reporters = rdb.Table(
"reporters",
metadata,
rdb.Column( "reporter_id", rdb.Integer, rdb.ForeignKey('users.user_id'), primary_key=True ),
rdb.Column( "initials", rdb.Unicode(4), nullable=False ),
)
The field 'initials' will be a required field.
In the descriptor you may define a field as required, this overrides the definition in the schema:
class UserDescriptor( ModelDescriptor ):
fields = [
dict( name="user_id", omit=True),
dict( name="middle_name", label=_(u"Middle Name"), required=True),
]
or using the property:
class UserDescriptor( ModelDescriptor ):
fields = [
dict( name="birth_country",
property = schema.Choice( title=_(u"Country of Birth"),
source=DatabaseSource(domain.Country,
'country_name', 'country_id'),
required=True )
),
]
Maximum length of Input
If the database has a restriction e.g. VARCHAR(16) the user has to be warned if the input does not fit
This is handled at database schema level.
Check Type of Input
make sure that in a number field you may input only numbers
This is handled at database schema level
Unique values
give the user a feedback if the value is already present
Custom validations
If we need a special validation for a certain field (e.g. an email) this can be defined at the descriptor.
class UserDescriptor( ModelDescriptor ):
fields = [
#dict( name="email", label=_(u"Email")),
dict( name="email",
property = schema.TextLine( title =_(u"Email"),
description=_(u"Email address"),
constraint=check_email,
required=True
),
),
dict( name="login", label=_(u"Login Name")),
]
The constraint check_mail is a function that returns True if the input is a valid mail address otherwise an exception will be raised whose message will be displayed to the user.
class NotAnEmailAddress(schema.ValidationError):
"""This is not a valid email address"""
def check_email( email ):
if EMAIL_RE.match( email ) is None:
raise NotAnEmailAddress(email)
return False
return True
EMAIL_RE = "([0-9a-zA-Z_&.+-]+!)*[0-9a-zA-Z_&.+-]+@(([0-9a-zA-Z]([0-9a-zA-Z-]*[0-9a-z-A-Z])?\.)+[a-zA-Z]{2,6}|([0-9]{1,3}\.){3}[0-9]{1,3})$"
Validate one field against another
Validations of this kind can be implemented using invariants.
There are two ways to go about this. One is supply a base interface with an invariant already defined. The second is an additional syntax via the descriptor. You can define a sequence of functions to act as invariants via the descriptor attribute schema_invariants. You'll need to raise an invariant exception
For example the date of death must be after the date of birth and if a user is dead he must have the status 'active_p = 'D''
class DeathBeforeLifeError(schema.interfaces.ValidationError):
"""One cannot die before being born"""
def DeathBeforeLife(User):
"""Check if date of death is after date of birth"""
if User.date_of_death is None: return
if User.date_of_death < User.date_of_birth:
raise DeathBeforeLifeError
def IsDeceased(User):
"""If a user is deceased a date of death must be given"""
if User.active_p is None:
if User.date_of_death is None:
return
else:
raise interface.Invalid("If a user is deceased he must have the status 'D'")
if User.active_p == 'D':
if User.date_of_death is None:
raise interface.Invalid("A Date of Death must be given if a user is deceased")
else:
if User.date_of_death is not None:
raise interface.Invalid("If a user is deceased he must have the status 'D'")
Add the functions to the descriptor:
class UserDescriptor( ModelDescriptor ):
fields = [
dict( name="user_id", omit=True),
dict( name="date_of_birth", label=_(u"Date of Birth")),
dict( name="date_of_death", label=_(u"Date of Death")),
dict( name="active_p", label=_(u"Active")),
]
schema_invariants = [DeathBeforeLife, IsDeceased]
Access the data of the parent to validate
field must be filled to constraints of the parent
example: a sitting date must be inside the dates for a session.