A bare-bones example of a custom datasource for use with Symphony 2.3.

sym-custom-datasource.php

<?php
    
    /**
     * Custom Datasource Skeleton
     * 
     * A bare-bones example of a custom datasource for use with Symphony 2.3
     * 
     * @author:     Ian Young
     * @email:      i.young@me.com
     * @date:       12.01.2014
     * @version:    1.0
     */

    // Dependencies
    require_once(TOOLKIT . '/class.datasource.php');

    Class datasourceName extends SectionDatasource 
    {

        /**
         * Datasource Params
         * Matching those provided in the visual editor.
         */
        
        public $dsParamROOTELEMENT = '';                // Name your custom XML node (no spaces)
        public $dsParamORDER = 'desc';                  // 'asc' or 'desc'
        public $dsParamPAGINATERESULTS = 'yes';         // 'yes' or 'no'
        public $dsParamLIMIT = '20';                    // Results per page if paginating
        public $dsParamSTARTPAGE = '1';                 // Page number to start from if paginating
        public $dsParamREQUIREDPARAM = '';              // Will only return results if this url-param is included
        public $dsParamPARAMOUTPUT = array();           // Filter by page params
        public $dsParamREDIRECTONEMPTY = 'no';          // Redirect location if no results
        public $dsParamSORT = 'system:id';              // Field to sort by (defaults to 'system:id')
        public $dsParamASSOCIATEDENTRYCOUNTS = 'no';    // Include a count of entries in associated entries?
        public $dsParamINCLUDEDELEMENTS = array();      // Fields to include in the XML output
        // public $dsParamCACHE = '86400';                 // For Cacheable Datasource extension
        
        /**
         * Examples
         */
        
        /**
         * An associative array setting field ID and url-params (with a default value of '0')
         */
        // public $dsParamFILTERS = array(
        //     '01' => '{$url-param1:0}',
        // );
        
        /**
         * An array of fields within the Section (the one we're querying) to return in the output XML
         */
        // public $dsParamINCLUDEDELEMENTS = array(
        //     'field1',
        //     'field2',
        //     'field3: formatted',
        // );
        
        /**
         * Constructor
         *
         * @param array $env Environment variables from the Frontend class which includes any params set by Symphony or Events or by other Datasources.
         * @param boolean $process_params If set to true, `Datasource::processParameters` will be called. By default this is true.
         */
        public function __construct($env = NULL, $process_params = true) 
        {
            parent::__construct($env, $process_params);

            // Accessor function to return this Datasource's dependencies
            // If 'chaining' datasources this is where you list the others involved.
            $this->_dependencies = array();
        }

        /**
         * Information to be displayed in the admin panel
         * 
         * @return array Returns an associative array of information about a datasource.
         */
        public function about() 
        {
            return array(
                'name' => 'Custom Datasource Name',
                'author' => array(
                    'name' => 'Ian Young',
                    'website' => '',
                    'email' => ''),
                'version' => 'Symphony 2.3.3',
                'release-date' => '2014-01-01T0:00:00+00:00'
            );
        }

        /**
         * This function is required in order to identify what section this Datasource is for. 
         * 
         * It is used in the datasource editor. It must remain intact. 
         * Other datasources may return a string here defining their datasource type when they do not query a section.
         */
        public function getSource() 
        {
            return '1';
        }

        /**
         * Admin Panel Editing. 
         * 
         * For custom datasources you usually want to set this to false.
         * 
         * @return boolean True if the Datasource can be edited, false otherwise. Defaults to false.
         */
        public function allowEditorToParse() 
        {
            return false;
        }

        /**
         * The main method of the datasource.
         *
         * The function argument "param_pool" gives you access to the parameter pool so that you can add 
         * parameters for use later in displaying a web page.
         *
         * You can insert additional content (XML) using the methods of the XMLElement class.
         * 
         * @param  array $param_pool The current parameter pool that this Datasource can use when filtering and finding Entries or data.
         * @return array $result     Returned XML elements, attributes, and parameters.     
         */
        public function execute(array &$param_pool = null) 
        {

            // Set the root element (defined above)
            $result = new XMLElement($this->dsParamROOTELEMENT);
        
            // Custom logic starts here...
            
            /**
             * Example custom query, iteration, & output to XML
             */
            
            // $query = "SELECT field1, field2, field3 
            //           FROM table_name 
            //           ORDER BY 'field2'";
            //           
            // $items = Symphony::Database()->fetch($query);

            // Loop through the result and build the XML
            // foreach($items as $item) {

            //     $id          = array('id' => $row['id']);                 // Add ID as an attribute to 'node'
            //     $node        = new XMLElement('node', false, $id);      // Create the 'node' node (group) with above attributes

            //     $element1    = new XMLElement('element1', $item['field1']);
            //     $element2    = new XMLElement('element2', $item['field2']);
            //     $element3    = new XMLElement('element3', $item['field3']);

            //     // Add the child nodes
            //     $node->appendChildArray(array(
            //         $element1, 
            //         $element2, 
            //         $element3
            //     ));

            //     // Output to XML
            //     $result->appendChild($node);

            // }

            // End custom logic

            /**
             * If no results
             * 
             * When there are no entries found by the Datasource, this parameter will
             * be set to true, which will inject the default Symphony 'No records found'
             * message into the datasource's result.
             */
            if($this->_force_empty_result) $result = $this->emptyXMLSet();

            // Output XML to the page
            return $result;
        }

    }