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|
"""
# create a mapper from a class and table object
usermapper = Mapper(User, users)
# get primary key
usermapper.get(10)
userlist = usermapper.select(usermapper.table.user_id == 10)
userlist = usermapper.select(
and_(usermapper.table.user_name == 'fred', usermapper.table.user_id == 12)
)
userlist = usermapper.select("user_id =12 and foo=bar", from_obj=["foo"])
usermapper = Mapper(
User,
users,
properties = {
'addresses' : Relation(addressmapper, lazy = False),
'permissions' : Relation(permissions,
# one or the other
associationtable = userpermissions,
criterion = and_(users.user_id == userpermissions.user_id, userpermissions.permission_id=permissions.permission_id),
lazy = True),
'*' : [users, userinfo]
},
)
addressmapper = Mapper(Address, addresses, properties = {
'street': addresses.address_1,
})
"""
import sqlalchemy.sql as sql
import sqlalchemy.schema as schema
import sqlalchemy.engine as engine
class Mapper(object):
def __init__(self, class_, selectable, table = None, properties = None, identitymap = None):
self.class_ = class_
self.selectable = selectable
if table is None:
self.table = self._find_table(selectable)
else:
self.table = table
self.props = {}
for column in self.selectable.columns:
self.props[column.key] = ColumnProperty(column)
if properties is not None:
for key, value in properties.iteritems():
self.props[key] = value
if identitymap is not None:
self.identitymap = identitymap
else:
self.identitymap = _global_identitymap
def instances(self, cursor):
result = []
cursor = engine.ResultProxy(cursor)
localmap = IdentityMap()
while True:
row = cursor.fetchone()
if row is None:
break
identitykey = self._identity_key(row)
if not localmap.has_key(identitykey):
instance = self._create(row, identitykey, localmap)
result.append(instance)
else:
for key, prop in self.props.iteritems():
prop.execute(instance, key, row, identitykey, localmap, True)
return result
def get(self, id):
"""returns an instance of the object based on the given ID."""
pass
def select(self, arg = None, **params):
"""selects instances of the object from the database.
arg can be any ClauseElement, which will form the criterion with which to
load the objects.
For more advanced usage, arg can also be a Select statement object, which
will be executed and its resulting rowset used to build new object instances.
in this case, the developer must insure that an adequate set of columns exists in the
rowset with which to build new object instances."""
if arg is not None and isinstance(arg, sql.Select):
return self._select_statement(arg, **params)
else:
return self._select_whereclause(arg, **params)
def save(self, object):
pass
def delete(self, whereclause = None, **params):
pass
class TableFinder(sql.ClauseVisitor):
def visit_table(self, table):
if hasattr(self, 'table'):
raise "Mapper can only create object instances against a single-table identity - specify the 'table' argument to the Mapper constructor"
self.table = table
def _find_table(self, selectable):
tf = Mapper.TableFinder()
selectable.accept_visitor(tf)
return tf.table
def _select_whereclause(self, whereclause = None, **params):
statement = sql.select([self.selectable], whereclause)
for key, value in self.props.iteritems():
value.setup(key, self.selectable, statement)
return self._select_statement(statement, **params)
def _select_statement(self, statement, **params):
statement.use_labels = True
return self.instances(statement.execute(**params))
def _identity_key(self, row):
return self.identitymap.get_key(row, self.class_, self.table, self.selectable)
def _create(self, row, identitykey, localmap):
instance = self.class_()
for column in self.selectable.primary_keys:
if row[column.label] is None:
return None
for key, prop in self.props.iteritems():
prop.execute(instance, key, row, identitykey, localmap, False)
self.identitymap[identitykey] = instance
localmap[identitykey] = instance
return instance
class MapperProperty:
def execute(self, instance, key, row, isduplicate):
raise NotImplementedError()
def setup(self, key, primarytable, statement):
pass
class ColumnProperty(MapperProperty):
def __init__(self, column):
self.column = column
def execute(self, instance, key, row, identitykey, localmap, isduplicate):
if not isduplicate:
setattr(instance, key, row[self.column.label])
class EagerLoader(MapperProperty):
def __init__(self, mapper, whereclause):
self.mapper = mapper
self.whereclause = whereclause
def setup(self, key, primarytable, statement):
targettable = self.mapper.selectable
if hasattr(statement, '_outerjoin'):
statement._outerjoin = sql.outerjoin(statement._outerjoin, targettable, self.whereclause)
else:
statement._outerjoin = sql.outerjoin(primarytable, targettable, self.whereclause)
statement.append_from(statement._outerjoin)
statement.append_column(targettable)
def execute(self, instance, key, row, identitykey, localmap, isduplicate):
try:
list = getattr(instance, key)
except AttributeError:
list = []
setattr(instance, key, list)
identitykey = self.mapper._identity_key(row)
if not localmap.has_key(identitykey):
subinstance = self.mapper._create(row, identitykey, localmap)
list.append(subinstance)
class IdentityMap(dict):
def get_key(self, row, class_, table, selectable):
return (class_, table, tuple([row[column.label] for column in selectable.primary_keys]))
_global_identitymap = IdentityMap()
|
