source: main/waeup.sirp/trunk/src/waeup/sirp/utils/importexport.txt @ 6045

Importing and Exporting Things
******************************

The waeup package tries to support all special object types to be
exportable and importable.

.. :doctest:
.. :layer: waeup.sirp.testing.WAeUPSIRPUnitTestLayer

As imports and exports of data are a cruical point when doing updates
or to enable data backups, this support must be considered a serious
topic for the base functionality of the whole software.

Exports and imports are implemented using the Zope component framework
capabilities. This means we need some adapters and utilities, which we
register, by grokking the whole package. This is done on startup
automatically, but in doctests (like this one) it is done by the
testlayer.

Furthermore we need something to import/export. As only pickable
classes are importable/exportable and these have to be defined in some
globally reachable module, we first define some silly object in
filesystem and adjust the path to lookup modules:

    >>> import os
    >>> import sys
    >>> os.mkdir('stoneage')
    >>> old_sys_path = sys.path
    >>> open(os.path.join('stoneage', '__init__.py'), 'wb').write(
    ... """
    ... class Cave(object):
    ...   name = 'Unnamed cave'
    ...   dinoports = 2
    ... """)
    >>> sys.path.append(os.getcwd())

Now we can import stoneage.Cave objects.


Exporting XML
=============

One of the major formats we support for data export is XML.

When we want to export an object, we can choose the destination
file. If we do not give a file to write to, we get a StringIO object,
i.e. an in-memory file.

We can export caves. First we create a cave:

    >>> from stoneage import Cave
    >>> mycave = Cave()
    >>> mycave.name = 'Freds Cave'
    >>> mycave.dinoports = 1

Exporting plain XML
-------------------

Now let's export it to XML. To do this we first ask the framework for
an exporter::

    >>> from waeup.sirp.interfaces import IWAeUPXMLExporter
    >>> exporter = IWAeUPXMLExporter(mycave)
    >>> exporter
    <waeup.sirp.utils.importexport.XMLExporter object at 0x...>

All exporters provide an ``export(<obj>)`` method::

    >>> result = exporter.export()

The result is an object of type StringIO. We therefore use its
`read()` method to get the actual XML data::

    >>> print result.read()
    <?xml version="1.0" encoding="utf-8" ?>...


Generating XML files
--------------------

We can also let the results be written to a file::

    >>> result = exporter.export('myexport.xml')
    >>> print open('myexport.xml', 'rb').read()
    <?xml version="1.0" encoding="utf-8" ?>
    <pickle>
      <object>
    ...
    </pickle>


Importing XML
=============

We can generate objects from XML.

We change the name of the cave:

    >>> mycave.name = 'Another name'

Now we create an importer for that object:

    >>> from waeup.sirp.interfaces import IWAeUPXMLImporter
    >>> importer = IWAeUPXMLImporter(mycave)

Importing from filenames
------------------------

We can use a filepath to import from the denoted file::

    >>> new_obj = importer.doImport('myexport.xml')

The object created is indeed a cave::

    >>> new_obj
    <stoneage.Cave object at 0x...>

    >>> new_obj.name
    'Freds Cave'

The new object is really a new object::

    >>> new_obj is mycave
    False

Importing from filelike objects
-------------------------------

We can also pass a file-like object instead of a filepath::

    >>> filelike_obj = open('myexport.xml', 'rb')
    >>> new_obj = importer.doImport(filelike_obj)

The object created is indeed a faculty::

    >>> new_obj
    <stoneage.Cave object at 0x...>

Clean up::

    >>> import os
    >>> import shutil
    >>> sys.path = old_sys_path
    >>> os.unlink('myexport.xml')
    >>> shutil.rmtree('stoneage')