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9441ffb165
Caller now has to do it. No need to avoid circular deps, no need to do much of anything at all.
205 lines
7.8 KiB
Python
205 lines
7.8 KiB
Python
from functools import partial
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from sqlalchemy.ext.associationproxy import association_proxy
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from sqlalchemy.orm import aliased, compile_mappers, mapper, relationship, synonym
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from sqlalchemy.orm.collections import attribute_mapped_collection
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from sqlalchemy.orm.scoping import ScopedSession
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from sqlalchemy.orm.session import Session, object_session
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from sqlalchemy.schema import Column, ForeignKey, Table
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from sqlalchemy.sql.expression import and_, bindparam, select
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from sqlalchemy.types import Integer
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def create_translation_table(_table_name, foreign_class, relation_name,
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language_class, relation_lazy='select', **kwargs):
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"""Creates a table that represents some kind of data attached to the given
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foreign class, but translated across several languages. Returns the new
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table's mapped class. It won't be declarative, but it will have a
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`__table__` attribute so you can retrieve the Table object.
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`foreign_class` must have a `__singlename__`, currently only used to create
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the name of the foreign key column.
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Also supports the notion of a default language, which is attached to the
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session. This is English by default, for historical and practical reasons.
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Usage looks like this:
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class Foo(Base): ...
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create_translation_table('foo_bars', Foo, 'bars',
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name = Column(...),
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)
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# Now you can do the following:
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foo.name
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foo.name_map['en']
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foo.foo_bars['en']
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foo.name_map['en'] = "new name"
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del foo.name_map['en']
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q.options(joinedload(Foo.bars_local))
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q.options(joinedload(Foo.bars))
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The following properties are added to the passed class:
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- `(relation_name)`, a relation to the new table. It uses a dict-based
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collection class, where the keys are language identifiers and the values
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are rows in the created tables.
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- `(relation_name)_local`, a relation to the row in the new table that
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matches the current default language.
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- `(relation_name)_class`, the class created by this function.
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Note that these are distinct relations. Even though the former necessarily
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includes the latter, SQLAlchemy doesn't treat them as linked; loading one
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will not load the other. Modifying both within the same transaction has
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undefined behavior.
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For each column provided, the following additional attributes are added to
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Foo:
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- `(column)_map`, an association proxy onto `foo_bars`.
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- `(column)`, an association proxy onto `foo_bars_local`.
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Pardon the naming disparity, but the grammar suffers otherwise.
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Modifying these directly is not likely to be a good idea.
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"""
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# n.b.: language_class only exists for the sake of tests, which sometimes
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# want to create tables entirely separate from the pokedex metadata
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foreign_key_name = foreign_class.__singlename__ + '_id'
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Translations = type(_table_name, (object,), {
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'_language_identifier': association_proxy('local_language', 'identifier'),
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})
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# Create the table object
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table = Table(_table_name, foreign_class.__table__.metadata,
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Column(foreign_key_name, Integer, ForeignKey(foreign_class.id),
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primary_key=True, nullable=False,
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info=dict(description="ID of the %s these texts relate to" % foreign_class.__singlename__)),
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Column('local_language_id', Integer, ForeignKey(language_class.id),
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primary_key=True, nullable=False,
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info=dict(description="Language these texts are in")),
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)
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Translations.__table__ = table
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# Add ye columns
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# Column objects have a _creation_order attribute in ascending order; use
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# this to get the (unordered) kwargs sorted correctly
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kwitems = kwargs.items()
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kwitems.sort(key=lambda kv: kv[1]._creation_order)
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for name, column in kwitems:
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column.name = name
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table.append_column(column)
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# Construct ye mapper
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mapper(Translations, table, properties={
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'foreign_id': synonym(foreign_key_name),
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'local_language': relationship(language_class,
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primaryjoin=table.c.local_language_id == language_class.id,
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innerjoin=True),
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})
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# Add full-table relations to the original class
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# Foo.bars_table
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setattr(foreign_class, relation_name + '_table', Translations)
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# Foo.bars
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setattr(foreign_class, relation_name, relationship(Translations,
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primaryjoin=foreign_class.id == Translations.foreign_id,
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collection_class=attribute_mapped_collection('local_language'),
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))
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# Foo.bars_local
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# This is a bit clever; it uses bindparam() to make the join clause
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# modifiable on the fly. db sessions know the current language and
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# populate the bindparam.
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# The 'dummy' value is to trick SQLA; without it, SQLA thinks this
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# bindparam is just its own auto-generated clause and everything gets
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# fucked up.
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local_relation_name = relation_name + '_local'
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setattr(foreign_class, local_relation_name, relationship(Translations,
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primaryjoin=and_(
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Translations.foreign_id == foreign_class.id,
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Translations.local_language_id == bindparam('_default_language_id',
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value='dummy', type_=Integer, required=True),
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),
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foreign_keys=[Translations.foreign_id, Translations.local_language_id],
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uselist=False,
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#innerjoin=True,
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lazy=relation_lazy,
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))
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# Add per-column proxies to the original class
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for name, column in kwitems:
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# Class.(column) -- accessor for the default language's value
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setattr(foreign_class, name,
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association_proxy(local_relation_name, name))
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# Class.(column)_map -- accessor for the language dict
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# Need a custom creator since Translations doesn't have an init, and
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# these are passed as *args anyway
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def creator(language, value):
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row = Translations()
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row.local_language = language
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setattr(row, name, value)
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return row
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setattr(foreign_class, name + '_map',
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association_proxy(relation_name, name, creator=creator))
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# Add to the list of translation classes
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foreign_class.translation_classes.append(Translations)
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# Done
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return Translations
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class MultilangSession(Session):
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"""A tiny Session subclass that adds support for a default language.
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Caller will need to assign something to `default_language` before this will
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actually work.
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"""
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_default_language_id = 0 # Better fill this in, caller
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def __init__(self, *args, **kwargs):
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self.language_class = kwargs.pop('language_class')
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super(MultilangSession, self).__init__(*args, **kwargs)
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@property
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def default_language(self):
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return self.query(self.language_class) \
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.filter_by(id=self._default_language_id) \
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.one()
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@default_language.setter
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def default_language(self, new):
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self._default_language_id = new.id
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@default_language.deleter
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def default_language(self):
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try:
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del self._default_language_id
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except AttributeError:
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pass
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def execute(self, clause, params=None, *args, **kwargs):
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if not params:
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params = {}
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params.setdefault('_default_language_id', self._default_language_id)
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return super(MultilangSession, self).execute(
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clause, params, *args, **kwargs)
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class MultilangScopedSession(ScopedSession):
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"""Dispatches language selection to the attached Session."""
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@property
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def default_language(self):
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return self.registry().default_language
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@default_language.setter
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def default_language(self, new):
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self.registry().default_language = new
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def remove(self):
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del self.registry().default_language
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super(MultilangScopedSession, self).remove()
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