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             lazy='joined'),
 104     })
 105
 106     # Add full-table relations to the original class
 107     # Foo.bars_table
 108     setattr(foreign_class, relation_name + '_table', Translations)
 109     # Foo.bars
 110     setattr(foreign_class, relation_name, relationship(Translations,
 111         primaryjoin=foreign_class.id == Translations.foreign_id,
 112         collection_class=attribute_mapped_collection('local_language'),
 113     ))
 114     # Foo.bars_local
 115     # This is a bit clever; it uses bindparam() to make the join clause
 116     # modifiable on the fly.  db sessions know the current language and
 117     # populate the bindparam.
 118     # The 'dummy' value is to trick SQLA; without it, SQLA thinks this
 119     # bindparam is just its own auto-generated clause and everything gets
 120     # fucked up.
 121     local_relation_name = relation_name + '_local'
 122     setattr(foreign_class, local_relation_name, relationship(Translations,
 123         primaryjoin=and_(
 124             Translations.foreign_id == foreign_class.id,
 125             Translations.local_language_id == bindparam('_default_language_id',
 126                 value='dummy', type_=Integer, required=True),
 127         ),
 128         foreign_keys=[Translations.foreign_id, Translations.local_language_id],
 129         uselist=False,
 130         #innerjoin=True,
 131         lazy=relation_lazy,
 132     ))
 133
 134     # Add per-column proxies to the original class
 135     for name, column in kwitems:
 136         # Class.(column) -- accessor for the default language's value
 137         setattr(foreign_class, name,
 138             association_proxy(local_relation_name, name))
 139
 140         # Class.(column)_map -- accessor for the language dict
 141         # Need a custom creator since Translations doesn't have an init, and
 142         # these are passed as *args anyway
 143         def creator(language, value):
 144             row = Translations()
 145             row.local_language = language
 146             setattr(row, name, value)
 147             return row
 148         setattr(foreign_class, name + '_map',
 149             association_proxy(relation_name, name, creator=creator))
 150
 151     # Add to the list of translation classes
 152     foreign_class.translation_classes.append(Translations)
 153
 154     # Done
 155     return Translations
 156
 157 class MultilangSession(Session):
 158     """A tiny Session subclass that adds support for a default language.
 159
 160     Needs to be used with `MultilangScopedSession`, below.
 161     """
 162     default_language_id = None
 163
 164     def __init__(self, *args, **kwargs):
 165         if 'default_language_id' in kwargs:
 166             self.default_language_id = kwargs.pop('default_language_id')
 167
 168         super(MultilangSession, self).__init__(*args, **kwargs)
 169
 170     def execute(self, clause, params=None, *args, **kwargs):
 171         if not params:
 172             params = {}
 173         params.setdefault('_default_language_id', self.default_language_id)
 174
 175         return super(MultilangSession, self).execute(
 176             clause, params, *args, **kwargs)
 177
 178 class MultilangScopedSession(ScopedSession):
 179     """Dispatches language selection to the attached Session."""
 180
 181     def __init__(self, *args, **kwargs):
 182         super(MultilangScopedSession, self).__init__(*args, **kwargs)
 183
 184     @property
 185     def default_language_id(self):
 186         """Passes the new default language id through to the current session.
 187         """
 188         return self.registry().default_language_id
 189
 190     @default_language_id.setter
 191     def default_language_id(self, new):
 192         self.registry().default_language_id = new