New di.xml Rejects <preferences> node

[astorm]

In older version of Magento 2, it was possible to enact a Magento 1 class rewrite style behavior using a preferences node in a module's config.xml file.

<confg>
    <global>
        <di>
            <preferences>
                <Mage_Core_Model_Old>Packagename_Modulename_Mode_New</Mage_Core_Model_Old>
            </preferences>
        </di>
    </global>
</config>

However, rewrites specified in this manner are (appear to be?) ignored in the 2.0.0.0-dev50 version of Magento 2. This makes sense if a module's di.xml file is the new location for these nodes. However, creating the following nodes in di.xml

#File: app/code/Packagename/Modulename/etc/di.xml
<config>
            <preferences>
                <Mage_Core_Model_Old>Packagename_Modulename_Mode_New</Mage_Core_Model_Old>
            </preferences>
</config>

results in the following error.

Fatal error: Uncaught exception 'Exception' with message 'Invalid application config. Unknown node: preferences.' in /path/to/magento2/lib/Magento/ObjectManager/Config/Mapper/Dom.php on line 140
( ! ) Exception: Invalid application config. Unknown node: preferences. in /path/to/magento2/lib/Magento/ObjectManager/Config/Mapper/Dom.php on line 140
Call Stack
#   Time    Memory  Function    Location
1   0.0011  243056  {main}( )   ../index.php:0
2   0.0111  918664  Magento\Core\Model\EntryPoint\Http->processRequest( )   ../index.php:31
3   0.2358  4453456 Magento\Core\Model\AbstractEntryPoint->processException( )  ../Http.php:48
4   0.2358  4453792 Magento\Core\Model\AbstractEntryPoint->_init( ) ../AbstractEntryPoint.php:72
5   0.2358  4453928 Magento\Core\Model\ObjectManager->__construct( )    ../AbstractEntryPoint.php:110
6   0.2518  4822512 Magento\Core\Model\ObjectManager\ConfigLoader->load( )  ../ObjectManager.php:149
7   0.2519  4822632 Magento\Config\Reader\Filesystem->read( )   ../ConfigLoader.php:68
8   0.2540  4835528 Magento\Config\Reader\Filesystem->_readFiles( ) ../Filesystem.php:139
9   0.3746  4836216 Magento\ObjectManager\Config\Mapper\Dom->convert( ) ../Filesystem.php:179

If support for these so called <preferences/> rewrites have been dropped in favor of plugins, the release notes should indicate this. If support has not been dropped, support for preferences should be added to di.xml, or restored to config.xml.

[sshymko]

@astorm
Format of the DI config has changed, the correct format for rewrites would be:

#File: app/code/Packagename/Modulename/etc/di.xml
<config>
    <preference for="Mage_Core_Model_Old" type="Packagename_Modulename_Mode_New" />
</config>

[philwinkle]

@sshymko should it not be formatted as such?

<preference for="Mage\Core\Model\Old" type="Packagename\Modulename\Mode\New" />

[sshymko]

@philwinkle
Yes, current version does not contain classes Mage_Core_Model_*, but only Magento\Core\Model\*.
DI config should reference classes in exactly the same way they're referenced from PHP code, i.e. Packagename_Modulename_Mode_New or Packagename\Modulename\Mode\New depending on whether namespaces were used.

[verklov]

@astorm, please refer to the response from @sshymko as absolutely correct. There is some documentation publicly available here: https://wiki.magento.com/display/MAGE2DOC/Rewriting+Classes?src=search. However, please consider using namespaces as mentioned by @sshymko while not yet updated in the documentation.

We are closing this issue.