[wiki:DeveloperGuidelines#DeveloperGuidelines Developer Guidelines] | S3ReusableField
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= S3ReusableField =

'''{{{S3ReusableField}}}''' is a [http://en.wikipedia.org/wiki/DRY 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):

{{{#!python
person_id = S3ReusableField("person_id", "reference pr_person",
                            sortby = ["first_name", "middle_name", "last_name"],
                            requires = IS_NULL_OR(IS_ONE_OF(db, "pr_person.id",
                                                            person_represent,
                                                            orderby="pr_person.first_name",
                                                            sort=True,
                                                            error_message="Person must be specified!")),
                            represent = pr_person_represent,
                            label = T("Person"),
                            comment = pr_person_id_comment,
                            ondelete = "RESTRICT",
                            widget = S3PersonAutocompleteWidget())
}}}

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}}}''' object to generate a '''{{{Field}}}''' instance:

{{{#!python
tablename = "mytable"
self.define_table(tablename,
                  ...,
                  # Insert a Field("person_id") with the pre-defined parameters:
                  person_id(), 
                  ...)
}}}

'''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:

{{{#!python
tablename = mytable"
self.define_table(tablename,
                  ...,
                  # Insert a Field("reporter") with the attributes from person_id:
                  person_id("reporter",           
                            # also override the label:
                            label=T("Reporter"),
                            ),
                  ...)
}}}
== Deactivate IS_EMPTY_OR ==

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

{{{#!python
tablename = "my_table"
self.define_table(tablename,
                  ...,
                  # Inserts the person_id Field, but remove IS_EMPTY_OR from .requires:
                  person_id(empty=False), 
                  ...)
}}}
== Multiple Widgets ==

Besides the normal "widget" attribute to specify a form widget for the resuable field, it is also possible to specify multiple possible widget alternatives, and then apply them in the instances by name. 

To do so, use the "widget'''s'''" (plural!) attribute.

Example:

{{{#!python
organisation_id = S3ReusableField("organisation_id", "reference org_organisation",
                                  requires = IS_EMPTY_OR(IS_ONE_OF(db, "org_organisation.id",
                                                                   org_organisation_represent)),
                                  represent = org_organisation_represent,
                                  label = T("Organisation"),
                                  widgets = {"default": S3OrganisationAutocompleteWidget(default_from_profile=True),
                                             "hierarchical": S3HierarchyWidget(lookup = "org_organisation",
                                                                               represent = org_organisation_represent,
                                                                               multiple = False,
                                                                               leafonly = False,
                                                                               ),
                                             },
                                  )
}}}

Without override or explicit choice, the "default" widget would be used in Field instances.

    ''NB: one should avoid having both "widget" and "widgets" in the same S3ReusableField. However, where both are present, "widget" overrides the "default" alternative in "widgets".''

To choose a widget by name:

{{{#!python
tablename = "my_table"
self.define_table(tablename,
                  ...,
                  # Choose the "hierarchical" widget for this instance:
                  organisation_id(widget="hierarchical"),
                  ...
                  )
}}}

This is especially useful if the choice of the widget depends on a deployment setting.

However, every instance can still override all possible alternatives:

{{{#!python
tablename = "my_table"
self.define_table(tablename,
                  ...,
                  # Specify the widget explicitly:
                  organisation_id(widget=MyCustomWidget()),
                  ...
                  )
}}}

...or enforce the web2py standard widget for the field type:

{{{#!python
tablename = "my_table"
self.define_table(tablename,
                  ...,
                  # Enforce web2py standard widget for the field type:
                  organisation_id(widget=None),
                  ...
                  )
}}}

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DeveloperGuidelines