sep-005.rst

SEP	5
Title	ItemBuilder API
Author	Ismael Carnales, Pablo Hoffman
Created	2009-07-24
Status	Obsoleted by :doc:`sep-008`

SEP-005: Detailed ItemBuilder API use

Item class for examples:

#!python
class NewsItem(Item):
    url = fields.TextField()
    headline = fields.TextField()
    content = fields.TextField()
    published = fields.DateField()

gSetting expanders

#!python
class NewsItemBuilder(ItemBuilder):
    item_class = NewsItem

    headline = reducers.Reducer(extract, remove_tags(), unquote(), strip)

This approach will override the Reducer class for BuilderFields depending on their Item Field class:

• MultivaluedField = PassValue
• TextField = JoinStrings
• other = TakeFirst

gSetting reducers

#!python
class NewsItemBuilder(ItemBuilder):
    item_class = NewsItem

    headline = reducers.TakeFirst(extract, remove_tags(), unquote(), strip)
    published = reducers.Reducer(extract, remove_tags(), unquote(), strip)

As with the previous example this would select join_strings as the reducer for content

gSetting expanders/reducers new way

#!python
class NewsItemBuilder(ItemBuilder):
    item_class = NewsItem

    headline = BuilderField(extract, remove_tags(), unquote(), strip)
    content = BuilderField(extract, remove_tags(), unquote(), strip)

    class Reducer:
        headline = TakeFirst

gExtending ItemBuilder

#!python
class SiteNewsItemBuilder(NewsItemBuilder):
    published = reducers.Reducer(extract, remove_tags(), unquote(),
                                 strip, to_date('%d.%m.%Y'))

gExtending ItemBuilder using statich methods

#!python
class SiteNewsItemBuilder(NewsItemBuilder):
    published = reducers.Reducer(NewsItemBuilder.published, to_date('%d.%m.%Y'))

gUsing default_builder

#!python
class DefaultedNewsItemBuilder(ItemBuilder):
    item_class = NewsItem

    default_builder = reducers.Reducer(extract, remove_tags(), unquote(), strip)

This will use default_builder as the builder for every field in the item class. As a reducer is not set reducers will be set based on Item Field classess.

gReset default_builder for a field

#!python
class DefaultedNewsItemBuilder(ItemBuilder):
    item_class = NewsItem

    default_builder = reducers.Reducer(extract, remove_tags(), unquote(), strip)
    url = BuilderField()

gExtending default ItemBuilder

#!python
class SiteNewsItemBuilder(NewsItemBuilder):
    published = reducers.Reducer(extract, remove_tags(), unquote(), strip, to_date('%d.%m.%Y'))

gExtending default ItemBuilder using static methods

#!python
class SiteNewsItemBuilder(NewsItemBuilder):
    published = reducers.Reducer(NewsItemBuilder.default_builder, to_date('%d.%m.%Y'))