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
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
|
import logging
from contextlib import contextmanager
from Orange.util import Registry
log = logging.getLogger(__name__)
class BackendError(Exception):
pass
class Backend(metaclass=Registry):
"""Base class for SqlTable backends. Implementations should define
all of the methods defined below.
Parameters
----------
connection_params: dict
connection params
"""
display_name = ""
def __init__(self, connection_params):
self.connection_params = connection_params
@classmethod
def available_backends(cls):
"""Return a list of all available backends"""
return cls.registry.values()
# "meta" methods
def list_tables_query(self, schema=None):
"""Return a list of tuples (schema, table_name)
Parameters
----------
schema : Optional[str]
If set, only tables from schema should be listed
Returns
-------
A list of tuples
"""
raise NotImplementedError
def list_tables(self, schema=None):
"""Return a list of tables in database
Parameters
----------
schema : Optional[str]
If set, only tables from given schema will be listed
Returns
-------
A list of TableDesc objects, describing the tables in the database
"""
query = self.list_tables_query(schema)
with self.execute_sql_query(query) as cur:
tables = []
for schema, name in cur.fetchall():
sql = "{}.{}".format(
self.quote_identifier(schema),
self.quote_identifier(name)) if schema else self.quote_identifier(name)
tables.append(TableDesc(name, schema, sql))
return tables
def n_tables_query(self, schema=None) -> str:
"""Return a query to count tables in database.
Parameters
----------
schema : Optional[str]
If set, only tables from schema should be listed
Returns
-------
Query string.
"""
raise NotImplementedError
def n_tables(self, schema=None) -> int:
"""Return number of tables in database.
Parameters
----------
schema : Optional[str]
If set, only tables from given schema will be listed.
Returns
-------
Number of tables in the database.
"""
query = self.n_tables_query(schema)
with self.execute_sql_query(query) as cur:
res = cur.fetchone()
return res[0]
def get_fields(self, table_name):
"""Return a list of field names and metadata in the given table
Parameters
----------
table_name: str
Returns
-------
a list of tuples (field_name, *field_metadata)
both will be passed to create_variable
"""
query = self.create_sql_query(table_name, ["*"], limit=0)
with self.execute_sql_query(query) as cur:
return cur.description
def distinct_values_query(self, field_name: str, table_name: str) -> str:
"""
Generate query for getting distinct values of field
Parameters
----------
field_name : name of the field
table_name : name of the table or query to search
Returns
-------
The query for getting distinct values of field
"""
raise NotImplementedError
def get_distinct_values(self, field_name, table_name):
"""Return a list of distinct values of field
Parameters
----------
field_name : name of the field
table_name : name of the table or query to search
Returns
-------
List[str] of values
"""
query = self.distinct_values_query(field_name, table_name)
with self.execute_sql_query(query) as cur:
values = cur.fetchall()
if len(values) > 20:
return ()
else:
return tuple(str(x[0]) for x in values)
def create_variable(self, field_name, field_metadata,
type_hints, inspect_table=None):
"""Create variable based on field information
Parameters
----------
field_name : str
name do the field
field_metadata : tuple
data to guess field type from
type_hints : Domain
domain with variable templates
inspect_table : Option[str]
name of the table to expect the field values or None
if no inspection is to be performed
Returns
-------
Variable representing the field
"""
raise NotImplementedError
def count_approx(self, query):
"""Return estimated number of rows returned by query.
Parameters
----------
query : str
Returns
-------
Approximate number of rows
"""
raise NotImplementedError
# query related methods
def create_sql_query(
self, table_name, fields, filters=(),
group_by=None, order_by=None, offset=None, limit=None,
use_time_sample=None):
"""Construct an sql query using the provided elements.
Parameters
----------
table_name : str
fields : List[str]
filters : List[str]
group_by: List[str]
order_by: List[str]
offset: int
limit: int
use_time_sample: int
Returns
-------
string containing sql query
"""
raise NotImplementedError
@contextmanager
def execute_sql_query(self, query, params=None):
"""Context manager for execution of sql queries
Usage:
```
with backend.execute_sql_query("SELECT * FROM foo") as cur:
cur.fetch_all()
```
Parameters
----------
query : string
query to be executed
params: tuple
parameters to be passed to the query
Returns
-------
yields a cursor that can be used to access the data
"""
raise NotImplementedError
def quote_identifier(self, name):
"""Quote identifier name so it can be safely used in queries
Parameters
----------
name: str
name of the parameter
Returns
-------
quoted parameter that can be used in sql queries
"""
raise NotImplementedError
def unquote_identifier(self, quoted_name):
"""Remove quotes from identifier name
Used when sql table name is used in where parameter to
query special tables
Parameters
----------
quoted_name : str
Returns
-------
unquoted name
"""
raise NotImplementedError
class TableDesc:
def __init__(self, name, schema, sql):
self.name = name
self.schema = schema
self.sql = sql
def __str__(self):
return self.name
class ToSql:
def __init__(self, sql):
self.sql = sql
def __call__(self):
return self.sql
|
