18 

    19 This PyAMS module is used to handle inheritance between a parent object and a child which can

    20 "inherit" from some of it's properties, as long as they share the same "target" interface.

    21 

    22     >>> from zope.interface import implementer, Interface, Attribute

    23     >>> from zope.schema import TextLine

    24     >>> from zope.schema.fieldproperty import FieldProperty

    25 

    26     >>> from pyams_utils.adapter import adapter_config

    27     >>> from pyams_utils.interfaces.inherit import IInheritInfo

    28     >>> from pyams_utils.inherit import BaseInheritInfo, InheritedFieldProperty

    29     >>> from pyams_utils.registry import get_global_registry

    30 

    31 Let's start by creating a "content" interface, and a marker interface for objects for which we

    32 want to provide this interface:

    33 

    34     >>> class IMyInfoInterface(IInheritInfo):

    35     ...     '''Custom interface'''

    36     ...     value = TextLine(title="Custom attribute")

    37 

    38     >>> class IMyTargetInterface(Interface):

    39     ...     '''Target interface'''

    40 

    41     >>> @implementer(IMyInfoInterface)

    42     ... class MyInfo(BaseInheritInfo):

    43     ...     target_interface = IMyTargetInterface

    44     ...     adapted_interface = IMyInfoInterface

    45     ...

    46     ...     _value = FieldProperty(IMyInfoInterface['value'])

    47     ...     value = InheritedFieldProperty(IMyInfoInterface['value'])

    48 

    49 Please note that for each field of the interface which can be inherited, you must define to

    50 properties: one using "InheritedFieldProperty" with the name of the field, and one using a classic

    51 "FieldProperty" with the same name prefixed by "_"; this property is used to store the "local"

    52 property value, when inheritance is unset.

    53 

    54 The adapter is created to adapt an object providing IMyTargetInterface to IMyInfoInterface;

    55 please note that the adapter *must* attach the created object to it's parent by setting

    56 __parent__ attribute:

    57 

    58     >>> @adapter_config(context=IMyTargetInterface, provides=IMyInfoInterface)

    59     ... def my_info_factory(context):

    60     ...     info = getattr(context, '__info__', None)

    61     ...     if info is None:

    62     ...         info = context.__info__ = MyInfo()

    63     ...         info.__parent__ = context

    64     ...     return info

    65 

    66 Adapter registration is here only for testing; the "adapter_config" decorator may do the job in

    67 a normal application context:

    68 

    69     >>> registry = get_global_registry()

    70     >>> registry.registerAdapter(my_info_factory, (IMyTargetInterface, ), IMyInfoInterface)

    71 

    72 We can then create classes which will be adapted to support inheritance:

    73 

    74     >>> @implementer(IMyTargetInterface)

    75     ... class MyTarget:

    76     ...     '''Target class'''

    77     ...     __parent__ = None

    78     ...     __info__ = None

    79 

    80     >>> parent = MyTarget()

    81     >>> parent_info = IMyInfoInterface(parent)

    82     >>> parent.__info__

    83     <pyams_utils.tests.test_utils...MyInfo object at ...>

    84     >>> parent_info.value = 'parent'

    85     >>> parent_info.value

    86     'parent'

    87     >>> parent_info.can_inherit

    88     False

    89 

    90 As soon as a parent is defined, the child object can inherit from it's parent:

    91 

    92     >>> child = MyTarget()

    93     >>> child.__parent__ = parent

    94     >>> child_info = IMyInfoInterface(child)

    95     >>> child.__info__

    96     <pyams_utils.tests.test_utils...MyInfo object at ...>

    97 

    98     >>> child_info.can_inherit

    99     True

   100     >>> child_info.inherit

   101     True

   102     >>> child_info.value

   103     'parent'

   104 

   105 Setting child value while inheritance is enabled donesn't have any effect:

   106 

   107     >>> child_info.value = 'child'

   108     >>> child_info.value

   109     'parent'

   110     >>> child_info.inherit_from == parent

   111     True

   112 

   113 You can disable inheritance and define your own value:

   114 

   115     >>> child_info.inherit = False

   116     >>> child_info.value = 'child'

   117     >>> child_info.value

   118     'child'

   119     >>> child_info.inherit_from == child

   120     True

   121 

   122 Please note that parent and child in this example share the same class, but this is not a

   123 requirement; they just have to implement the same marker interface, to be adapted to the same

   124 content interface.

   136 __docformat__ = 'restructuredtext'

   137 

   138