Coverage for .tox/coverage/lib/python3.11/site-packages/wuttjamaican/db/handler.py: 100%

1# -*- coding: utf-8; -*- 

2################################################################################ 

3# 

4# WuttJamaican -- Base package for Wutta Framework 

5# Copyright © 2024 Lance Edgar 

6# 

7# This file is part of Wutta Framework. 

8# 

9# Wutta Framework is free software: you can redistribute it and/or modify it 

10# under the terms of the GNU General Public License as published by the Free 

11# Software Foundation, either version 3 of the License, or (at your option) any 

12# later version. 

13# 

14# Wutta Framework is distributed in the hope that it will be useful, but 

15# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 

16# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for 

17# more details. 

18# 

19# You should have received a copy of the GNU General Public License along with 

20# Wutta Framework. If not, see <http://www.gnu.org/licenses/>. 

21# 

22################################################################################ 

23""" 

24Database Handler 

25""" 

26 

27import sqlalchemy as sa 

28 

29from wuttjamaican.app import GenericHandler 

30 

31 

32class DatabaseHandler(GenericHandler): 

33 """ 

34 Base class and default implementation for the :term:`db handler`. 

35 """ 

36 

37 def next_counter_value(self, session, key): 

38 """ 

39 Return the next counter value for the given key. 

40 

41 If the DB backend is PostgreSQL, then a proper "sequence" is 

42 used for the counter. 

43 

44 All other backends use a "fake" sequence by creating a 

45 dedicated table with auto-increment primary key, to provide 

46 the counter. 

47 

48 :param session: Current :term:`db session`. 

49 

50 :param key: Unique key indicating the counter for which the 

51 next value should be fetched. 

52 

53 :returns: Next value as integer. 

54 """ 

55 dialect = session.bind.url.get_dialect().name 

56 

57 # postgres uses "true" native sequence 

58 if dialect == 'postgresql': 

59 sql = f"create sequence if not exists {key}_seq" 

60 session.execute(sa.text(sql)) 

61 sql = f"select nextval('{key}_seq')" 

62 value = session.execute(sa.text(sql)).scalar() 

63 return value 

64 

65 # otherwise use "magic" workaround 

66 engine = session.bind 

67 metadata = sa.MetaData() 

68 table = sa.Table(f'_counter_{key}', metadata, 

69 sa.Column('value', sa.Integer(), primary_key=True)) 

70 table.create(engine, checkfirst=True) 

71 with engine.begin() as cxn: 

72 result = cxn.execute(table.insert()) 

73 return result.lastrowid