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arski7 on 09/27/07

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SqlAlchemy Versionable


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  1. """
  2. Test of Versionable using extensions
  3.  
  4. Why does the before_update or before_insert not cause the
  5. items added to the lists to save? If you call save
  6. twice they do?
  7. """
  8.  
  9. from sqlalchemy import *
  10. from sqlalchemy.orm import *
  11.  
  12. metadata = MetaData('sqlite://')
  13.  
  14. #######
  15. class VersionExt(MapperExtension):
  16. """will update changes"""
  17. def before_update(self, mapper, connection, instance):
  18. instance._doversion()
  19. return EXT_CONTINUE
  20.  
  21. def before_insert(self, mapper, connection, instance):
  22. instance._doversion()
  23. return EXT_CONTINUE
  24.  
  25.  
  26. version_table = Table("version", metadata,
  27. Column("id", Integer, primary_key=True),
  28. Column('assoc_id', None, ForeignKey('version_associations.assoc_id')),
  29. Column("whatchanged", String(255), nullable=False),
  30. Column("version", Integer),
  31. )
  32.  
  33.  
  34. ## association table
  35. version_associations_table = Table("version_associations", metadata,
  36. Column('assoc_id', Integer, primary_key=True),
  37. Column('type', String(50), nullable=False),
  38. Column('version', Integer, default=0),
  39. )
  40.  
  41. class Version(object):
  42. def __init__(self, chg):
  43. self.whatchanged = chg
  44. member = property(lambda self: getattr(self.association, '_backref_%s' % self.association.type))
  45.  
  46. class VersionAssoc(object):
  47. def __init__(self, name):
  48. self.type = name
  49.  
  50. def versionable(cls, name, uselist=True):
  51. """versionable 'interface'.
  52.  
  53.  
  54. """
  55. mapper = class_mapper(cls)
  56. table = mapper.local_table
  57. mapper.add_property('version_rel', relation(VersionAssoc, backref='_backref_%s' % table.name))
  58.  
  59. if uselist:
  60. # list based property decorator
  61. def get(self):
  62. if self.version_rel is None:
  63. self.version_rel = VersionAssoc(table.name)
  64. return self.version_rel.versions
  65. setattr(cls, name, property(get))
  66. else:
  67. # scalar based property decorator
  68. def get(self):
  69. return self.version_rel.versions[0]
  70. def set(self, value):
  71. if self.version_rel is None:
  72. self.version_rel = VersionAssoc(table.name)
  73. self.version_rel.versions = [value]
  74. setattr(cls, name, property(get, set))
  75.  
  76. mapper(Version, version_table)
  77.  
  78. mapper(VersionAssoc, version_associations_table, properties={
  79. 'versions':relation(Version, backref='association'),
  80. })
  81.  
  82. ######
  83. # sample # 1, users
  84.  
  85. users = Table("users", metadata,
  86. Column('id', Integer, primary_key=True),
  87. Column('name', String(50), nullable=False),
  88. # this column ties the users table into the change association
  89. Column('assoc_id', None, ForeignKey('version_associations.assoc_id'))
  90. )
  91.  
  92. class User(object):
  93. def _doversion(self):
  94. v1 = Version('what was changed?')
  95. self.versions.append(v1)
  96. v1.version = 1
  97. print ' in _doversion '
  98.  
  99. mapper(User, users, extension=VersionExt())
  100. versionable(User, 'versions', uselist=True)
  101.  
  102. ######
  103. # use it !
  104. metadata.create_all()
  105.  
  106. u1 = User()
  107. u1.name = 'bob'
  108.  
  109.  
  110. sess = create_session()
  111. sess.save(u1)
  112. sess.flush()
  113. # uncommenting these saves causes the versions to now be saved?
  114. # sess.save(u1)
  115. # sess.flush()
  116. sess.clear()
  117.  
  118. # query objects, get their versions
  119.  
  120. bob = sess.query(User).filter_by(name='bob').first()
  121. print [v.whatchanged for v in bob.versions]
  122. if bob.versions:
  123. print 'bob changed: %s ct = %s ' % (bob.versions[0].whatchanged, len(bob.versions))
  124. else:
  125. print 'no versions'

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