[wiki:DeveloperGuidelines] | S3ReusableField
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= S3ReusableField =

'''{{{S3ReusableField}}}''' is a DRY helper class for re-usable '''{{{Field}}}''' definitions.

== Define a S3ReusableField ==

A '''{{{S3ReusableField}}}''' is to be defined like a normal [http://web2py.com/book/default/chapter/06?search=Field#DAL,-Table,-Field Field] (though outside any '''{{{Table}}}''' definitions):

{{{
person_id = S3ReusableField("person_id", db.pr_person,
                            sortby = ["first_name", "middle_name", "last_name"],
                            requires = IS_NULL_OR(IS_ONE_OF(db, "pr_person.id",
                                                            shn_pr_person_represent,
                                                            orderby="pr_person.first_name",
                                                            sort=True,
                                                            error_message="Person must be specified!")),
                            represent = lambda id: (id and \
                                        [shn_pr_person_represent(id)] or [NONE])[0],
                            label = T("Person"),
                            comment = shn_person_id_comment,
                            ondelete = "RESTRICT",
                            widget = S3PersonAutocompleteWidget(request))
}}}

This definition does '''not''' create a '''{{{Field}}}''' instance, but just holds the parameters.

== Use S3ReusableFields in Table Definitions ==

To use this in a '''{{{Table}}}''' definition, just call the S3ReusableField instance object to generate a '''{{{Field}}}''' instance:

{{{
resourcename = "mytable"
tablename = "%s_%s" % (module, resourcename)
table = db.define_table(tablename,
                        ...,
                        person_id(), # inserts a Field("person_id") with the pre-defined parameters
                        ...,
                        migrate=migrate)
}}}

'''Note:''' If the '''{{{S3ReusableField}}}''' contains the '''{{{sortby}}}''' attribute, then a '''{{{FieldS3}}}''' instance is generated instead of '''{{{Field}}}'''
== Override Field Attributes ==

You can override the name and any attributes when generating the '''{{{Field}}}''' instance, by just re-specifying them:

{{{
resourcename = "mytable"
tablename = "%s_%s" % (module, resourcename)
table = db.define_table(tablename,
                        ...,
                        person_id("reporter",           # inserts a Field("reporter") with the attributes from person_id,
                                  label=T("Reporter")), # but replaces the label attribute by T("Reporter")
                        ...,
                        migrate=migrate)
}}}

== Deactivate IS_EMPTY_OR ==

To deactivate a '''{{{IS_NULL_OR}}}''' ('''{{{IS_EMPTY_OR}}}''') validator in the '''{{{S3ReusableField}}}''' when generating the '''{{{Field}}}''' instance, you can use the special attribute '''{{{empty}}}''':

{{{
resourcename = "mytable"
tablename = "%s_%s" % (module, resourcename)
table = db.define_table(tablename,
                        ...,
                        person_id(empty=False), # inserts the person_id Field, but removes IS_NULL_OR from .requires
                        ...,
                        migrate=migrate)
}}}

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DeveloperGuidelines