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e1bbe78b72
* SQLAlchemy 1.0 introduced "baked queries" - a way to construct Query objects so that they can be cached and reused. * SQLAlchemy 1.2 changed lazyloaded columns to use baked queries under the hood. * Our MultilangQuery class attempts to set _default_language_id right before the query is executed by overriding the __iter__ method. * Baked queries bypass the __iter__ method and call a lower-level method, _execute_and_instances, directly. * This caused problems where _default_language_id wouldn't get set correctly on lazyloaded columns. * To fix, make MultilangQuery override the _execute_and_instances method instead of __iter__. * This is really just a stopgap: the root cause is that query params are not preserved across lazyloads. Tested with SQLAlchemy 0.9.7, 1.1.18, and 1.2.5. Updates #236.
255 lines
10 KiB
Python
255 lines
10 KiB
Python
from sqlalchemy.ext.associationproxy import association_proxy, AssociationProxy
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from sqlalchemy.orm import Query, 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, exists
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from sqlalchemy.sql.operators import ColumnOperators
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from sqlalchemy.types import Integer
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from pokedex.db import markdown
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class LocalAssociationProxy(AssociationProxy, ColumnOperators):
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"""An association proxy for names in the default language
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Over the regular association_proxy, this provides sorting and filtering
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capabilities, implemented via SQL subqueries.
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"""
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def __clause_element__(self):
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q = select([self.remote_attr])
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q = q.where(self.target_class.foreign_id == self.owning_class.id)
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q = q.where(self.target_class.local_language_id == bindparam('_default_language_id'))
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return q
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def operate(self, op, *other, **kwargs):
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q = select([self.remote_attr])
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q = q.where(self.target_class.foreign_id == self.owning_class.id)
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q = q.where(self.target_class.local_language_id == bindparam('_default_language_id'))
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q = q.where(op(self.remote_attr, *other))
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return exists(q)
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def _getset_factory_factory(column_name, string_getter):
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"""Hello! I am a factory for creating getset_factory functions for SQLA.
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I exist to avoid the closure-in-a-loop problem.
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"""
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def getset_factory(underlying_type, instance):
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def getter(translations):
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if translations is None:
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return None
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text = getattr(translations, column_name)
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if text is None:
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return text
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session = object_session(translations)
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language = translations.local_language
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return string_getter(text, session, language)
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def setter(translations, value):
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# The string must be set on the Translation directly.
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raise AttributeError("Cannot set %s" % column_name)
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return getter, setter
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return getset_factory
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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)_table`, 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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For Markdown-formatted columns, `(column)_map` and `(column)` will give
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Markdown objects.
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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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'relation_name': relation_name,
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'__tablename__': _table_name,
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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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doc=u"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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doc=u"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 = list(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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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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getset_factory = None
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string_getter = column.info.get('string_getter')
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if string_getter:
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getset_factory = _getset_factory_factory(
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column.name, string_getter)
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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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LocalAssociationProxy(local_relation_name, name,
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getset_factory=getset_factory))
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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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getset_factory=getset_factory))
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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 MultilangQuery(Query):
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def _execute_and_instances(self, *args, **kwargs):
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# Set _default_language_id param if it hasn't been set by the time the query is executed.
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# XXX This is really hacky and we should figure out a cleaner method.
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if '_default_language_id' not in self._params or self._params['_default_language_id'] == 'dummy':
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self._params = self._params.copy()
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self._params['_default_language_id'] = self.session.default_language_id
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return super(MultilangQuery, self)._execute_and_instances(*args, **kwargs)
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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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Needs to be used with `MultilangScopedSession`, below.
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"""
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default_language_id = None
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markdown_extension_class = markdown.PokedexLinkExtension
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def __init__(self, *args, **kwargs):
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if 'default_language_id' in kwargs:
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self.default_language_id = kwargs.pop('default_language_id')
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markdown_extension_class = kwargs.pop('markdown_extension_class',
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self.markdown_extension_class)
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self.markdown_extension = markdown_extension_class(self)
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kwargs.setdefault('query_cls', MultilangQuery)
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super(MultilangSession, self).__init__(*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_id(self):
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"""Passes the new default language id through to the current session.
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"""
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return self.registry().default_language_id
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@default_language_id.setter
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def default_language_id(self, new):
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self.registry().default_language_id = new
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@property
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def markdown_extension(self):
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return self.registry().markdown_extension
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