pokedex/db/multilang.py

   1 from functools import partial
   2
   3 from sqlalchemy.ext.associationproxy import association_proxy
   4 from sqlalchemy.orm import aliased, compile_mappers, mapper, relationship, synonym
   5 from sqlalchemy.orm.collections import attribute_mapped_collection
   6 from sqlalchemy.orm.scoping import ScopedSession
   7 from sqlalchemy.orm.session import Session, object_session
   8 from sqlalchemy.schema import Column, ForeignKey, Table
   9 from sqlalchemy.sql.expression import and_, bindparam, select
  10 from sqlalchemy.types import Integer
  11
  12 def create_translation_table(_table_name, foreign_class, relation_name,
  13     language_class, relation_lazy='select', **kwargs):
  14     """Creates a table that represents some kind of data attached to the given
  15     foreign class, but translated across several languages.  Returns the new
  16     table's mapped class.  It won't be declarative, but it will have a
  17     `__table__` attribute so you can retrieve the Table object.
  18
  19     `foreign_class` must have a `__singlename__`, currently only used to create
  20     the name of the foreign key column.
  21
  22     Also supports the notion of a default language, which is attached to the
  23     session.  This is English by default, for historical and practical reasons.
  24
  25     Usage looks like this:
  26
  27         class Foo(Base): ...
  28
  29         create_translation_table('foo_bars', Foo, 'bars',
  30             name = Column(...),
  31         )
  32
  33         # Now you can do the following:
  34         foo.name
  35         foo.name_map['en']
  36         foo.foo_bars['en']
  37
  38         foo.name_map['en'] = "new name"
  39         del foo.name_map['en']
  40
  41         q.options(joinedload(Foo.bars_local))
  42         q.options(joinedload(Foo.bars))
  43
  44     The following properties are added to the passed class:
  45
  46     - `(relation_name)`, a relation to the new table.  It uses a dict-based
  47       collection class, where the keys are language identifiers and the values
  48       are rows in the created tables.
  49     - `(relation_name)_local`, a relation to the row in the new table that
  50       matches the current default language.
  51     - `(relation_name)_class`, the class created by this function.
  52
  53     Note that these are distinct relations.  Even though the former necessarily
  54     includes the latter, SQLAlchemy doesn't treat them as linked; loading one
  55     will not load the other.  Modifying both within the same transaction has
  56     undefined behavior.
  57
  58     For each column provided, the following additional attributes are added to
  59     Foo:
  60
  61     - `(column)_map`, an association proxy onto `foo_bars`.
  62     - `(column)`, an association proxy onto `foo_bars_local`.
  63
  64     Pardon the naming disparity, but the grammar suffers otherwise.
  65
  66     Modifying these directly is not likely to be a good idea.
  67     """
  68     # n.b.: language_class only exists for the sake of tests, which sometimes
  69     # want to create tables entirely separate from the pokedex metadata
  70
  71     foreign_key_name = foreign_class.__singlename__ + '_id'
  72
  73     Translations = type(_table_name, (object,), {
  74         '_language_identifier': association_proxy('local_language', 'identifier'),
  75     })
  76
  77     # Create the table object
  78     table = Table(_table_name, foreign_class.__table__.metadata,
  79         Column(foreign_key_name, Integer, ForeignKey(foreign_class.id),
  80             primary_key=True, nullable=False,
  81             info=dict(description="ID of the %s these texts relate to" % foreign_class.__singlename__)),
  82         Column('local_language_id', Integer, ForeignKey(language_class.id),
  83             primary_key=True, nullable=False,
  84             info=dict(description="Language these texts are in")),
  85     )
  86     Translations.__table__ = table
  87
  88     # Add ye columns
  89     # Column objects have a _creation_order attribute in ascending order; use
  90     # this to get the (unordered) kwargs sorted correctly
  91     kwitems = kwargs.items()
  92     kwitems.sort(key=lambda kv: kv[1]._creation_order)
  93     for name, column in kwitems:
  94         column.name = name
  95         table.append_column(column)
  96
  97     # Construct ye mapper
  98     mapper(Translations, table, properties={
  99         'foreign_id': synonym(foreign_key_name),
 100         'local_language': relationship(language_class,
 101             primaryjoin=table.c.local_language_id == language_class.id,
 102             innerjoin=True),
 103     })
 104
 105     # Add full-table relations to the original class
 106     # Foo.bars_table
 107     setattr(foreign_class, relation_name + '_table', Translations)
 108     # Foo.bars
 109     setattr(foreign_class, relation_name, relationship(Translations,
 110         primaryjoin=foreign_class.id == Translations.foreign_id,
 111         collection_class=attribute_mapped_collection('local_language'),
 112     ))
 113     # Foo.bars_local
 114     # This is a bit clever; it uses bindparam() to make the join clause
 115     # modifiable on the fly.  db sessions know the current language and
 116     # populate the bindparam.
 117     # The 'dummy' value is to trick SQLA; without it, SQLA thinks this
 118     # bindparam is just its own auto-generated clause and everything gets
 119     # fucked up.
 120     local_relation_name = relation_name + '_local'
 121     setattr(foreign_class, local_relation_name, relationship(Translations,
 122         primaryjoin=and_(
 123             Translations.foreign_id == foreign_class.id,
 124             Translations.local_language_id == bindparam('_default_language_id',
 125                 value='dummy', type_=Integer, required=True),
 126         ),
 127         foreign_keys=[Translations.foreign_id, Translations.local_language_id],
 128         uselist=False,
 129         #innerjoin=True,
 130         lazy=relation_lazy,
 131     ))
 132
 133     # Add per-column proxies to the original class
 134     for name, column in kwitems:
 135         # Class.(column) -- accessor for the default language's value
 136         setattr(foreign_class, name,
 137             association_proxy(local_relation_name, name))
 138
 139         # Class.(column)_map -- accessor for the language dict
 140         # Need a custom creator since Translations doesn't have an init, and
 141         # these are passed as *args anyway
 142         def creator(language, value):
 143             row = Translations()
 144             row.local_language = language
 145             setattr(row, name, value)
 146             return row
 147         setattr(foreign_class, name + '_map',
 148             association_proxy(relation_name, name, creator=creator))
 149
 150     # Add to the list of translation classes
 151     foreign_class.translation_classes.append(Translations)
 152
 153     # Done
 154     return Translations
 155
 156 class MultilangSession(Session):
 157     """A tiny Session subclass that adds support for a default language.
 158
 159     Needs to be used with `MultilangScopedSession`, below.
 160     """
 161     default_language_id = None
 162
 163     def __init__(self, *args, **kwargs):
 164         if 'default_language_id' in kwargs:
 165             self.default_language_id = kwargs.pop('default_language_id')
 166
 167         super(MultilangSession, self).__init__(*args, **kwargs)
 168
 169     def execute(self, clause, params=None, *args, **kwargs):
 170         if not params:
 171             params = {}
 172         params.setdefault('_default_language_id', self.default_language_id)
 173
 174         return super(MultilangSession, self).execute(
 175             clause, params, *args, **kwargs)
 176
 177 class MultilangScopedSession(ScopedSession):
 178     """Dispatches language selection to the attached Session."""
 179
 180     def __init__(self, *args, **kwargs):
 181         super(MultilangScopedSession, self).__init__(*args, **kwargs)
 182
 183     @property
 184     def default_language_id(self):
 185         """Passes the new default language id through to the current session.
 186         """
 187         return self.registry().default_language_id
 188
 189     @default_language_id.setter
 190     def default_language_id(self, new):
 191         self.registry().default_language_id = new