How do I create self-relationships in polymorphic inheritance in Elixir and Pylons?
- by Turukawa
I am new to programming and am following the example in the Pylons documentation on creating a Wiki. The database I want to link to the wiki was created with Elixir so I rewrote the Wiki database schema and have continued from there.
In the wiki there is a requirement for a Navigation table which is inherited by Pages and Sections. A section can have many pages, while a page can only have one section. In addition, each sibling node can be chain-referenced to each other.
So:
Nav has "section" (OneToMany) and "before" (OneToOne - to reference preceeding node)
Page has "section" (ManyToOne - many pages in one section) and inherits "before"
Section inherits all from Nav
The code I've written looks like this:
class Nav(Entity):
using_options(inheritance='multi')
name = Field(Unicode(30), default=u'Untitled Node')
path = Field(Unicode(255), default=u'')
section = OneToMany('Page', inverse='section')
after = OneToOne('Nav', inverse='before')
before = OneToMany('Nav', inverse='after')
class Page(Nav):
using_options(inheritance='multi')
content = Field(UnicodeText, nullable=False)
posted = Field(DateTime, default=now())
title = Field(Unicode(255), default=u'Untitled Page')
heading = Field(Unicode(255))
tags = ManyToMany('Tag')
comments = OneToMany('Comment')
section = ManyToOne('Nav', inverse='section')
class Section(Nav):
using_options(inheritance='multi')
Errors received on this:
sqlalchemy.exc.OperationalError: (OperationalError) table nav has no column named aftr_id u'INSERT INTO nav (name, path, aftr_id, row_type) VALUES (?, ?, ?, ?)'
I've also tried:
before = ManyToMany('Nav', inverse='before')
on Nav in the hopes this might break the problem, but also not.
The original SQLAlchemy code from the tutorial for these declarations is as follows:
nav_table = schema.Table('nav', meta.metadata,
schema.Column('id', types.Integer(),
schema.Sequence('nav_id_seq', optional=True), primary_key=True),
schema.Column('name', types.Unicode(255), default=u'Untitled Node'),
schema.Column('path', types.Unicode(255), default=u''),
schema.Column('section', types.Integer(), schema.ForeignKey('nav.id')),
schema.Column('before', types.Integer(), default=None),
schema.Column('type', types.String(30), nullable=False)
)
page_table = schema.Table('page', meta.metadata,
schema.Column('id', types.Integer, schema.ForeignKey('nav.id'), primary_key=True),
schema.Column('content', types.Text(), nullable=False),
schema.Column('posted', types.DateTime(), default=now),
schema.Column('title', types.Unicode(255), default=u'Untitled Page'),
schema.Column('heading', types.Unicode(255)),
)
section_table = sa.Table('section', meta.metadata,
schema.Column('id', types.Integer,
schema.ForeignKey('nav.id'), primary_key=True),
)
orm.mapper(Nav, nav_table, polymorphic_on=nav_table.c.type, polymorphic_identity='nav')
orm.mapper(Section, section_table, inherits=Nav, polymorphic_identity='section')
orm.mapper(Page, page_table, inherits=Nav, polymorphic_identity='page', properties={
'comments':orm.relation(Comment, backref='page', cascade='all'),
'tags':orm.relation(Tag, secondary=pagetag_table)
})
Any help is much appreciated.
