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SEP	5
Title	ItemBuilder API
Author	Ismael Carnales, Pablo Hoffman
Created	2009-07-24
Status	Obsoleted by :doc:`sep-008` System Message: ERROR/3 (`<stdin>`, line 7); backlink Unknown interpreted text role "doc".

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 classes.

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'))

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SEP-005: Detailed ItemBuilder API use