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
|
"""
# 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
class Mapper:
def __init__(self, class_, table, properties = None, identitymap = None):
self.class_ = class_
self.table = table
self.props = {}
if properties is not None:
for key, column in properties.iteritems():
desc = (key, column)
self.props["key_" + key] = desc
self.props["column_" + column.label] = desc
self.props["column_" + column.name] = desc
else:
for column in table.columns:
desc = (column.name, column)
self.props["key_" + column.name] = desc
self.props["column_" + column.label] = desc
self.props["column_" + column.name] = desc
if identitymap is not None:
self.identitymap = identitymap
else:
self.identitymap = _global_identitymap
def _create(self, row):
instance = self.class_()
for desc in self.props.values():
setattr(instance, desc[0], row[desc[1].name])
return instance
def instance(self, row):
return self.identitymap.get(row, self.class_, self.table, creator = self._create)
def get(self, id):
"""returns an instance of the object based on the given ID."""
pass
def _select_whereclause(self, whereclause = None, **params):
statement = sql.select([self.table], whereclause)
return self._select_statement(statement, **params)
def _select_statement(self, statement, **params):
result = []
cursor = ResultProxy(statement.execute(**params))
while True:
row = cursor.fetchone()
if row is None:
break
result.append(self.instance(row))
return result
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 ResultProxy:
def __init__(self, cursor):
self.cursor = cursor
metadata = cursor.description
self.props = {}
i = 0
for item in metadata:
self.props[item[0]] = i
self.props[i] = i
i+=1
def fetchone(self):
row = self.cursor.fetchone()
if row is not None:
return RowProxy(self, row)
else:
return None
class RowProxy:
def __init__(self, parent, row):
self.parent = parent
self.row = row
def __getitem__(self, key):
return self.row[self.parent.props[key]]
class IdentityMap:
def __init__(self):
self.map = {}
self.keystereotypes = {}
def get(self, row, class_, table, creator = None):
"""given a database row, a class to be instantiated, and a table corresponding
to the row, returns a corrseponding object instance, if any, from the identity
map. the primary keys specified in the table will be used to indicate which
columns from the row form the effective key of the instance."""
key = (class_, table, tuple([row[column.name] for column in table.primary_keys]))
try:
return self.map[key]
except KeyError:
return self.map.setdefault(key, creator(row))
_global_identitymap = IdentityMap()
|
