/usr/share/pyshared/elixir/ext/associable.py is in python-elixir 0.7.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 | '''
Associable Elixir Statement Generator
==========
Associable
==========
About Polymorphic Associations
------------------------------
A frequent pattern in database schemas is the has_and_belongs_to_many, or a
many-to-many table. Quite often multiple tables will refer to a single one
creating quite a few many-to-many intermediate tables.
Polymorphic associations lower the amount of many-to-many tables by setting up
a table that allows relations to any other table in the database, and relates
it to the associable table. In some implementations, this layout does not
enforce referential integrity with database foreign key constraints, this
implementation uses an additional many-to-many table with foreign key
constraints to avoid this problem.
.. note:
SQLite does not support foreign key constraints, so referential integrity
can only be enforced using database backends with such support.
Elixir Statement Generator for Polymorphic Associations
-------------------------------------------------------
The ``associable`` function generates the intermediary tables for an Elixir
entity that should be associable with other Elixir entities and returns an
Elixir Statement for use with them. This automates the process of creating the
polymorphic association tables and ensuring their referential integrity.
Matching select_XXX and select_by_XXX are also added to the associated entity
which allow queries to be run for the associated objects.
Example usage:
.. sourcecode:: python
class Tag(Entity):
name = Field(Unicode)
acts_as_taggable = associable(Tag)
class Entry(Entity):
title = Field(Unicode)
acts_as_taggable('tags')
class Article(Entity):
title = Field(Unicode)
acts_as_taggable('tags')
Or if one of the entities being associated should only have a single member of
the associated table:
.. sourcecode:: python
class Address(Entity):
street = Field(String(130))
city = Field(String(100))
is_addressable = associable(Address, 'addresses')
class Person(Entity):
name = Field(Unicode)
orders = OneToMany('Order')
is_addressable()
class Order(Entity):
order_num = Field(primary_key=True)
item_count = Field(Integer)
person = ManyToOne('Person')
is_addressable('address', uselist=False)
home = Address(street='123 Elm St.', city='Spooksville')
user = Person(name='Jane Doe')
user.addresses.append(home)
neworder = Order(item_count=4)
neworder.address = home
user.orders.append(neworder)
# Queries using the added helpers
Person.select_by_addresses(city='Cupertino')
Person.select_addresses(and_(Address.c.street=='132 Elm St',
Address.c.city=='Smallville'))
Statement Options
-----------------
The generated Elixir Statement has several options available:
+---------------+-------------------------------------------------------------+
| Option Name | Description |
+===============+=============================================================+
| ``name`` | Specify a custom name for the Entity attribute. This is |
| | used to declare the attribute used to access the associated |
| | table values. Otherwise, the name will use the plural_name |
| | provided to the associable call. |
+---------------+-------------------------------------------------------------+
| ``uselist`` | Whether or not the associated table should be represented |
| | as a list, or a single property. It should be set to False |
| | when the entity should only have a single associated |
| | entity. Defaults to True. |
+---------------+-------------------------------------------------------------+
| ``lazy`` | Determines eager loading of the associated entity objects. |
| | Defaults to False, to indicate that they should not be |
| | lazily loaded. |
+---------------+-------------------------------------------------------------+
'''
from elixir.statements import Statement
import sqlalchemy as sa
__doc_all__ = ['associable']
def associable(assoc_entity, plural_name=None, lazy=True):
'''
Generate an associable Elixir Statement
'''
interface_name = assoc_entity._descriptor.tablename
able_name = interface_name + 'able'
if plural_name:
attr_name = "%s_rel" % plural_name
else:
plural_name = interface_name
attr_name = "%s_rel" % interface_name
class GenericAssoc(object):
def __init__(self, tablename):
self.type = tablename
#TODO: inherit from entity builder
class Associable(object):
"""An associable Elixir Statement object"""
def __init__(self, entity, name=None, uselist=True, lazy=True):
self.entity = entity
self.lazy = lazy
self.uselist = uselist
if name is None:
self.name = plural_name
else:
self.name = name
def after_table(self):
col = sa.Column('%s_assoc_id' % interface_name, sa.Integer,
sa.ForeignKey('%s.id' % able_name))
self.entity._descriptor.add_column(col)
if not hasattr(assoc_entity, '_assoc_table'):
metadata = assoc_entity._descriptor.metadata
association_table = sa.Table("%s" % able_name, metadata,
sa.Column('id', sa.Integer, primary_key=True),
sa.Column('type', sa.String(40), nullable=False),
)
tablename = "%s_to_%s" % (able_name, interface_name)
association_to_table = sa.Table(tablename, metadata,
sa.Column('assoc_id', sa.Integer,
sa.ForeignKey(association_table.c.id,
ondelete="CASCADE"),
primary_key=True),
#FIXME: this assumes a single id col
sa.Column('%s_id' % interface_name, sa.Integer,
sa.ForeignKey(assoc_entity.table.c.id,
ondelete="RESTRICT"),
primary_key=True),
)
assoc_entity._assoc_table = association_table
assoc_entity._assoc_to_table = association_to_table
def after_mapper(self):
if not hasattr(assoc_entity, '_assoc_mapper'):
assoc_entity._assoc_mapper = sa.orm.mapper(
GenericAssoc, assoc_entity._assoc_table, properties={
'targets': sa.orm.relation(
assoc_entity,
secondary=assoc_entity._assoc_to_table,
lazy=lazy, backref='associations',
order_by=assoc_entity.mapper.order_by)
})
entity = self.entity
entity.mapper.add_property(
attr_name,
sa.orm.relation(GenericAssoc, lazy=self.lazy,
backref='_backref_%s' % entity.table.name)
)
if self.uselist:
def get(self):
if getattr(self, attr_name) is None:
setattr(self, attr_name,
GenericAssoc(entity.table.name))
return getattr(self, attr_name).targets
setattr(entity, self.name, property(get))
else:
# scalar based property decorator
def get(self):
attr = getattr(self, attr_name)
if attr is not None:
return attr.targets[0]
else:
return None
def set(self, value):
if getattr(self, attr_name) is None:
setattr(self, attr_name,
GenericAssoc(entity.table.name))
getattr(self, attr_name).targets = [value]
setattr(entity, self.name, property(get, set))
# self.name is both set via mapper synonym and the python
# property, but that's how synonym properties work.
# adding synonym property after "real" property otherwise it
# breaks when using SQLAlchemy > 0.4.1
entity.mapper.add_property(self.name, sa.orm.synonym(attr_name))
# add helper methods
def select_by(cls, **kwargs):
return cls.query.join([attr_name, 'targets']) \
.filter_by(**kwargs).all()
setattr(entity, 'select_by_%s' % self.name, classmethod(select_by))
def select(cls, *args, **kwargs):
return cls.query.join([attr_name, 'targets']) \
.filter(*args, **kwargs).all()
setattr(entity, 'select_%s' % self.name, classmethod(select))
return Statement(Associable)
|