Extending models and controllers in an extbase TYPO3 extension

ext_tables.php

<?php

// Table you're modifying
t3lib_div::loadTCA('tx_news_domain_model_news');

// TCA config, arbitrary example: simple text field - nice to include your ext's name in its name so you remember where it's from
$tempColumns = array (
	'tx_myext_new_input' => array (
		'exclude' => 0,
		'label' => 'Some new input field',
		'config' => array(
			'type' => 'input',
			'size' => 10,
			'eval' => 'trim'
			)
		)
	)
	// More if you want
);

// Add new fields to the TCA
t3lib_extMgm::addTCAcolumns('tx_news_domain_model_news', $tempColumns, 1);

// Optional: tell typo3 where to put the new fields in the BE 
// default is to just put them at the end of the 'Extended' tab if you don't include this
t3lib_extMgm::addToAllTCAtypes('tx_news_domain_model_news','tx_myext_domain_model_news');

// Don't forget to update your DB and clear your cache

ext_tables.sql

#
# Add to table structure for the original extension
#
CREATE TABLE tx_news_domain_model_news (
	tx_myext_new_input varchar(255) DEFAULT NULL
);

setup.txt

config.tx_extbase {
    objects {
        # Extending a controller
        Tx_News_Controller_NewsController {
                className = Tx_Myext_Controller_NewsController
        }
        # Here's the model
        Tx_News_Domain_Model_News {
            className = Tx_Myext_Domain_Model_News
        }
        # Note that if you're trying to extend a repository, you pretty much have to extend the model too,
        # even if you don't want to, because the alternative is extending extbase's Repository class and
        # changing how it looks for its model. Dumb.
    }
    # This is the important part for the model. Not necessary when extending a controller.
    persistence {
        classes {
            Tx_Myext_Domain_Model_News {
                mapping {
                    tableName = tx_news_domain_model_news
                    # If extending the Repository, you may need to get rid of this recordType line
                    recordType = Tx_News_Domain_Model_News  
                }
            }
        }
    }
}