moodle/lib/ddllib.php

<?php // $Id$

///////////////////////////////////////////////////////////////////////////
//                                                                       //
// NOTICE OF COPYRIGHT                                                   //
//                                                                       //
// Moodle - Modular Object-Oriented Dynamic Learning Environment         //
//          http://moodle.com                                            //
//                                                                       //
// Copyright (C) 2001-3001 Martin Dougiamas        http://dougiamas.com  //
//           (C) 2001-3001 Eloy Lafuente (stronk7) http://contiento.com  //
//                                                                       //
// This program is free software; you can redistribute it and/or modify  //
// it under the terms of the GNU General Public License as published by  //
// the Free Software Foundation; either version 2 of the License, or     //
// (at your option) any later version.                                   //
//                                                                       //
// This program is distributed in the hope that it will be useful,       //
// but WITHOUT ANY WARRANTY; without even the implied warranty of        //
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         //
// GNU General Public License for more details:                          //
//                                                                       //
//          http://www.gnu.org/copyleft/gpl.html                         //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

// This library includes all the required functions used to handle the DB
// structure (DDL) independently of the underlying RDBMS in use. All the functions
// rely on the XMLDBDriver classes to be able to generate the correct SQL
// syntax needed by each DB.
//
// To define any structure to be created we'll use the schema defined
// by the XMLDB classes, for tables, fields, indexes, keys and other
// statements instead of direct handling of SQL sentences.
//
// This library should be used, exclusively, by the installation and
// upgrade process of Moodle.
//
// For further documentation, visit http://docs.moodle.org/en/DDL_functions

/// Add required XMLDB constants
    require_once($CFG->libdir . '/xmldb/classes/XMLDBConstants.php');

/// Add main XMLDB Generator
    require_once($CFG->libdir . '/xmldb/classes/generators/XMLDBGenerator.class.php');

/// Add required XMLDB DB classes
    require_once($CFG->libdir . '/xmldb/classes/XMLDBObject.class.php');
    require_once($CFG->libdir . '/xmldb/classes/XMLDBFile.class.php');
    require_once($CFG->libdir . '/xmldb/classes/XMLDBStructure.class.php');
    require_once($CFG->libdir . '/xmldb/classes/XMLDBTable.class.php');
    require_once($CFG->libdir . '/xmldb/classes/XMLDBField.class.php');
    require_once($CFG->libdir . '/xmldb/classes/XMLDBKey.class.php');
    require_once($CFG->libdir . '/xmldb/classes/XMLDBIndex.class.php');
    require_once($CFG->libdir . '/xmldb/classes/XMLDBStatement.class.php');

/// Based on $CFG->dbtype, add the proper generator class
    if (!file_exists($CFG->libdir . '/xmldb/classes/generators/' . $CFG->dbtype . '/' . $CFG->dbtype . '.class.php')) {
        error ('DB Type: ' . $CFG->dbtype . ' not supported by XMLDDB');
    }
    require_once($CFG->libdir . '/xmldb/classes/generators/' . $CFG->dbtype . '/' . $CFG->dbtype . '.class.php');


/// Add other libraries
    require_once($CFG->libdir . '/xmlize.php');
/**
 * Add a new field to a table, or modify an existing one (if oldfield is defined).
 * Warning: Please be careful on primary keys, as this function will eat auto_increments
 *
 * @uses $CFG
 * @uses $db
 * @param string $table the name of the table to modify. (Without the prefix.)
 * @param string $oldfield If changing an existing column, the name of that column.
 * @param string $field The name of the column at the end of the operation.
 * @param string $type The type of the column at the end of the operation. TEXT, VARCHAR, CHAR, INTEGER, REAL, or TINYINT
 * @param string $size The size of that column type. As in VARCHAR($size), or INTEGER($size).
 * @param string $signed For numeric column types, whether that column is 'signed' or 'unsigned'.
 * @param string $default The new default value for the column.
 * @param string $null 'not null', or '' to allow nulls.
 * @param string $after Which column to insert this one after. Not supported on Postgres.
 *
 * @return boolean Wheter the operation succeeded.
 */
function table_column($table, $oldfield, $field, $type='integer', $size='10',
                      $signed='unsigned', $default='0', $null='not null', $after='') {
    global $CFG, $db, $empty_rs_cache;

    if (!empty($empty_rs_cache[$table])) {  // Clear the recordset cache because it's out of date
        unset($empty_rs_cache[$table]);
    }

    switch (strtolower($CFG->dbtype)) {

        case 'mysql':
        case 'mysqlt':

            switch (strtolower($type)) {
                case 'text':
                    $type = 'TEXT';
                    $signed = '';
                    break;
                case 'integer':
                    $type = 'INTEGER('. $size .')';
                    break;
                case 'varchar':
                    $type = 'VARCHAR('. $size .')';
                    $signed = '';
                    break;
                case 'char':
                    $type = 'CHAR('. $size .')';
                    $signed = '';
                    break;
            }

            if (!empty($oldfield)) {
                $operation = 'CHANGE '. $oldfield .' '. $field;
            } else {
                $operation = 'ADD '. $field;
            }

            $default = 'DEFAULT \''. $default .'\'';

            if (!empty($after)) {
                $after = 'AFTER `'. $after .'`';
            }

            return execute_sql('ALTER TABLE '. $CFG->prefix . $table .' '. $operation .' '. $type .' '. $signed .' '. $default .' '. $null .' '. $after);

        case 'postgres7':        // From Petri Asikainen
            //Check db-version
            $dbinfo = $db->ServerInfo();
            $dbver = substr($dbinfo['version'],0,3);

            //to prevent conflicts with reserved words
            $realfield = '"'. $field .'"';
            $field = '"'. $field .'_alter_column_tmp"';
            $oldfield = '"'. $oldfield .'"';

            switch (strtolower($type)) {
                case 'tinyint':
                case 'integer':
                    if ($size <= 4) {
                        $type = 'INT2';
                    }
                    if ($size <= 10) {
                        $type = 'INT';
                    }
                    if  ($size > 10) {
                        $type = 'INT8';
                    }
                    break;
                case 'varchar':
                    $type = 'VARCHAR('. $size .')';
                    break;
                case 'char':
                    $type = 'CHAR('. $size .')';
                    $signed = '';
                    break;
            }

            $default = '\''. $default .'\'';

            //After is not implemented in postgesql
            //if (!empty($after)) {
            //    $after = "AFTER '$after'";
            //}

            //Use transactions
            execute_sql('BEGIN');

            //Always use temporary column
            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ADD COLUMN '. $field .' '. $type);
            //Add default values
            execute_sql('UPDATE '. $CFG->prefix . $table .' SET '. $field .'='. $default);


            if ($dbver >= '7.3') {
                // modifying 'not null' is posible before 7.3
                //update default values to table
                if (strtoupper($null) == 'NOT NULL') {
                    execute_sql('UPDATE '. $CFG->prefix . $table .' SET '. $field .'='. $default .' WHERE '. $field .' IS NULL');
                    execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET '. $null);
                } else {
                    execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' DROP NOT NULL');
                }
            }

            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET DEFAULT '. $default);

            if ( $oldfield != '""' ) {

                // We are changing the type of a column. This may require doing some casts...
                $casting = '';
                $oldtype = column_type($table, $oldfield);
                $newtype = column_type($table, $field);

                // Do we need a cast?
                if($newtype == 'N' && $oldtype == 'C') {
                    $casting = 'CAST(CAST('.$oldfield.' AS TEXT) AS REAL)';
                }
                else if($newtype == 'I' && $oldtype == 'C') {
                    $casting = 'CAST(CAST('.$oldfield.' AS TEXT) AS INTEGER)';
                }
                else {
                    $casting = $oldfield;
                }

                // Run the update query, casting as necessary
                execute_sql('UPDATE '. $CFG->prefix . $table .' SET '. $field .' = '. $casting);
                execute_sql('ALTER TABLE  '. $CFG->prefix . $table .' DROP COLUMN '. $oldfield);
            }

            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' RENAME COLUMN '. $field .' TO '. $realfield);

            return execute_sql('COMMIT');

        default:
            switch (strtolower($type)) {
                case 'integer':
                    $type = 'INTEGER';
                    break;
                case 'varchar':
                    $type = 'VARCHAR';
                    break;
            }

            $default = 'DEFAULT \''. $default .'\'';

            if (!empty($after)) {
                $after = 'AFTER '. $after;
            }

            if (!empty($oldfield)) {
                execute_sql('ALTER TABLE '. $CFG->prefix . $table .' RENAME COLUMN '. $oldfield .' '. $field);
            } else {
                execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ADD COLUMN '. $field .' '. $type);
            }

            execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET '. $null);
            return execute_sql('ALTER TABLE '. $CFG->prefix . $table .' ALTER COLUMN '. $field .' SET '. $default);
    }
}

/**
 * Given one XMLDBTable, check if it exists in DB (true/false)
 *
 * @param XMLDBTable table to be searched for
 * @return boolean true/false
 */
function table_exists($table) {

    global $CFG, $db;

    $exists = true;

/// Do this function silenty (to avoid output in install/upgrade process)
    $olddbdebug = $db->debug;
    $db->debug = false;

/// Load the needed generator
    $classname = 'XMLDB' . $CFG->dbtype;
    $generator = new $classname();
    $generator->setPrefix($CFG->prefix);
/// Calculate the name of the table
    $tablename = $generator->getTableName($table, false);

/// Search such tablename in DB
    $metatables = $db->MetaTables();
    $metatables = array_flip($metatables);
    $metatables = array_change_key_case($metatables, CASE_LOWER);
    if (!array_key_exists($tablename,  $metatables)) {
        $exists = false;
    }

/// Re-set original debug 
    $db->debug = $olddbdebug;

    return $exists;
}

/**
 * Given one XMLDBField, check if it exists in DB (true/false)
 *
 * @uses, $db
 * @param XMLDBTable the table
 * @param XMLDBField the field to be searched for
 * @return boolean true/false
 */
function field_exists($table, $field) {

    global $CFG, $db;

    $exists = true;

/// Do this function silenty (to avoid output in install/upgrade process)
    $olddbdebug = $db->debug;
    $db->debug = false;

/// Check the table exists
    if (!table_exists($table)) {
        $db->debug = $olddbdebug; //Re-set original $db->debug
        return false;
    }

/// Load the needed generator
    $classname = 'XMLDB' . $CFG->dbtype;
    $generator = new $classname();
    $generator->setPrefix($CFG->prefix);
/// Calculate the name of the table
    $tablename = $generator->getTableName($table, false);

/// Get list of fields in table
    $fields = null;
    if ($fields = $db->MetaColumns($tablename)) {
        $fields = array_change_key_case($fields, CASE_LOWER);
    }

    if (!array_key_exists($field->getName(),  $fields)) {
        $exists = false;
    }

/// Re-set original debug 
    $db->debug = $olddbdebug;

    return $exists;
}

/**
 * Given one XMLDBIndex, check if it exists in DB (true/false)
 *
 * @uses, $db
 * @param XMLDBTable the table
 * @param XMLDBIndex the index to be searched for
 * @return boolean true/false
 */
function index_exists($table, $index) {

    global $CFG, $db;

    $exists = true;

/// Do this function silenty (to avoid output in install/upgrade process)
    $olddbdebug = $db->debug;
    $db->debug = false;

/// Wrap over find_index_name to see if the index exists
    if (!find_index_name($table, $index)) {
        $exists = false;
    }

/// Re-set original debug 
    $db->debug = $olddbdebug;

    return $exists;
}

/**
 * This function IS NOT IMPLEMENTED. ONCE WE'LL BE USING RELATIONAL
 * INTEGRITY IT WILL BECOME MORE USEFUL. FOR NOW, JUST CALCULATE "OFFICIAL"
 * KEY NAMES WITHOUT ACCESSING TO DB AT ALL.
 * Given one XMLDBKey, the function returns the name of the key in DB (if exists)
 * of false if it doesn't exist
 *
 * @uses, $db
 * @param XMLDBTable the table to be searched
 * @param XMLDBKey the key to be searched
 * @return string key name of false
 */
function find_key_name($table, $xmldb_key) {

    global $CFG, $db;

/// Extract key columns
    $keycolumns = $xmldb_key->getFields();

/// Get list of keys in table
/// first primaries (we aren't going to use this now, because the MetaPrimaryKeys is awful)
    ///TODO: To implement when we advance in relational integrity
/// then uniques (note that Moodle, for now, shouldn't have any UNIQUE KEY for now, but unique indexes)
    ///TODO: To implement when we advance in relational integrity (note that AdoDB hasn't any MetaXXX for this.
/// then foreign (note that Moodle, for now, shouldn't have any FOREIGN KEY for now, but indexes)
    ///TODO: To implement when we advance in relational integrity (note that AdoDB has one MetaForeignKeys()
    ///but it's far from perfect.
/// TODO: To create the proper functions inside each generator to retrieve all the needed KEY info (name
///       columns, reftable and refcolumns

/// So all we do is to return the official name of the requested key without any confirmation!)
    $classname = 'XMLDB' . $CFG->dbtype;
    $generator = new $classname();
    $generator->setPrefix($CFG->prefix);
/// One exception, harcoded primary constraint names
    if ($generator->primary_key_name && $xmldb_key->getType() == XMLDB_KEY_PRIMARY) {
        return $generator->primary_key_name;
    } else {
    /// Calculate the name suffix
        switch ($xmldb_key->getType()) {
            case XMLDB_KEY_PRIMARY:
                $suffix = 'pk';
                break;
            case XMLDB_KEY_UNIQUE:
                $suffix = 'uk';
                break;
            case XMLDB_KEY_FOREIGN_UNIQUE:
            case XMLDB_KEY_FOREIGN:
                $suffix = 'fk';
                break;
        }
    /// And simply, return the oficial name
        return $generator->getNameForObject($table->getName(), implode(', ', $xmldb_key->getFields()), $suffix);
    }
}

/**
 * Given one XMLDBIndex, the function returns the name of the index in DB (if exists)
 * of false if it doesn't exist
 *
 * @uses, $db
 * @param XMLDBTable the table to be searched
 * @param XMLDBIndex the index to be searched
 * @return string index name of false
 */
function find_index_name($table, $index) {

    global $CFG, $db;

/// Do this function silenty (to avoid output in install/upgrade process)
    $olddbdebug = $db->debug;
    $db->debug = false;

/// Extract index columns
    $indcolumns = $index->getFields();

/// Check the table exists
    if (!table_exists($table)) {
        $db->debug = $olddbdebug; //Re-set original $db->debug
        return false;
    }

/// Load the needed generator
    $classname = 'XMLDB' . $CFG->dbtype;
    $generator = new $classname();
    $generator->setPrefix($CFG->prefix);
/// Calculate the name of the table
    $tablename = $generator->getTableName($table, false);

/// Get list of indexes in table
    $indexes = null;
    if ($indexes = $db->MetaIndexes($tablename)) {
        $indexes = array_change_key_case($indexes, CASE_LOWER);
    }

/// Iterate over them looking for columns coincidence
    if ($indexes) {
        foreach ($indexes as $indexname => $index) {
            $columns = $index['columns'];
        /// Lower case column names
            $columns = array_flip($columns);
            $columns = array_change_key_case($columns, CASE_LOWER);
            $columns = array_flip($columns);
        /// Check if index matchs queried index
            $diferences = array_merge(array_diff($columns, $indcolumns), array_diff($indcolumns, $columns));
        /// If no diferences, we have find the index
            if (empty($diferences)) {
                $db->debug = $olddbdebug; //Re-set original $db->debug
                return $indexname;
            }
        }
    }
/// Arriving here, index not found
    $db->debug = $olddbdebug; //Re-set original $db->debug
    return false;
}

/**
 * Given one XMLDBTable, the function returns the name of its sequence in DB (if exists)
 * of false if it doesn't exist
 *
 * @param XMLDBTable the table to be searched
 * @return string sequence name of false
 */
function find_sequence_name($table) {

    global $CFG, $db;

    $sequencename = false;

/// Do this function silenty (to avoid output in install/upgrade process)
    $olddbdebug = $db->debug;
    $db->debug = false;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        $db->debug = $olddbdebug; //Re-set original $db->debug
        return false;
    }

/// Check table exists
    if (!table_exists($table)) {
        debugging('Table ' . $table->getName() . ' do not exist. Sequence not found', DEBUG_DEVELOPER);
        $db->debug = $olddbdebug; //Re-set original $db->debug
        return false; //Table doesn't exist, nothing to do
    }

    $sequencename = $table->getSequenceFromDB($CFG->dbtype, $CFG->prefix);

    $db->debug = $olddbdebug; //Re-set original $db->debug
    return $sequencename;
}

/**
 * This function will load one entire XMLDB file, generating all the needed
 * SQL statements, specific for each RDBMS ($CFG->dbtype) and, finally, it
 * will execute all those statements against the DB.
 *
 * @uses $CFG, $db
 * @param $file full path to the XML file to be used
 * @return boolean (true on success, false on error)
 */
function install_from_xmldb_file($file) {

    global $CFG, $db;

    $status = true;


    $xmldb_file = new XMLDBFile($file);

    if (!$xmldb_file->fileExists()) {
        return false;
    }

    $loaded = $xmldb_file->loadXMLStructure();
    if (!$loaded || !$xmldb_file->isLoaded()) {
    /// Show info about the error if we can find it
        if ($structure =& $xmldb_file->getStructure()) {
            if ($errors = $structure->getAllErrors()) {
                notify('Errors found in XMLDB file: '. implode (', ', $errors));
            }
        }
        return false;
    }

    $structure = $xmldb_file->getStructure();

    if (!$sqlarr = $structure->getCreateStructureSQL($CFG->dbtype, $CFG->prefix, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr);
}

/**
 * This function will create the table passed as argument with all its
 * fields/keys/indexes/sequences, everything based in the XMLDB object
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function create_table($table, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }

/// Check table doesn't exist
    if (table_exists($table)) {
        debugging('Table ' . $table->getName() . ' exists. Create skipped', DEBUG_DEVELOPER);
        return true; //Table exists, nothing to do
    }

    if(!$sqlarr = $table->getCreateTableSQL($CFG->dbtype, $CFG->prefix, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will drop the table passed as argument
 * and all the associated objects (keys, indexes, constaints, sequences, triggers)
 * will be dropped too.
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function drop_table($table, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }

/// Check table exists
    if (!table_exists($table)) {
        debugging('Table ' . $table->getName() . ' do not exist. Delete skipped', DEBUG_DEVELOPER);
        return true; //Table don't exist, nothing to do
    }

    if(!$sqlarr = $table->getDropTableSQL($CFG->dbtype, $CFG->prefix, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will rename the table passed as argument
 * Before renaming the index, the function will check it exists
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param string new name of the index
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function rename_table($table, $newname, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }

/// Check table exists
    if (!table_exists($table)) {
        debugging('Table ' . $table->getName() . ' do not exist. Rename skipped', DEBUG_DEVELOPER);
        return true; //Table doesn't exist, nothing to do
    }

/// Check newname isn't empty
    if (!$newname) {
        debugging('New name for table ' . $index->getName() . ' is empty! Rename skipped', DEBUG_DEVELOPER);
        return true; //Table doesn't exist, nothing to do
    }

    if(!$sqlarr = $table->getRenameTableSQL($CFG->dbtype, $CFG->prefix, $newname, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will add the field to the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function add_field($table, $field, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($field)) != 'xmldbfield') {
        return false;
    }

/// Check the field doesn't exist
    if (field_exists($table, $field)) {
        debugging('Field ' . $field->getName() . ' exists. Create skipped', DEBUG_DEVELOPER);
        return true;
    }

/// If NOT NULL and no default given, check the table is empty
    if ($field->getNotNull() && $field->getDefault() === NULL && count_records($table->getName())) {
        debugging('Field ' . $field->getName() . ' cannot be added. Not null fields added to non empty tables require default value. Create skipped', DEBUG_DEVELOPER);
         return true;
    }

    if(!$sqlarr = $table->getAddFieldSQL($CFG->dbtype, $CFG->prefix, $field, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will drop the field from the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (just the name is mandatory)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function drop_field($table, $field, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($field)) != 'xmldbfield') {
        return false;
    }

/// Check the field exists
    if (!field_exists($table, $field)) {
        debugging('Field ' . $field->getName() . ' do not exist. Delete skipped', DEBUG_DEVELOPER);
        return true;
    }

    if(!$sqlarr = $table->getDropFieldSQL($CFG->dbtype, $CFG->prefix, $field, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will change the type of the field in the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function change_field_type($table, $field, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($field)) != 'xmldbfield') {
        return false;
    }

    if(!$sqlarr = $table->getAlterFieldSQL($CFG->dbtype, $CFG->prefix, $field, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will change the precision of the field in the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function change_field_precision($table, $field, $continue=true, $feedback=true) {

/// Just a wrapper over change_field_type. Does exactly the same processing
    return change_field_type($table, $field, $continue, $feedback);
}

/**
 * This function will change the unsigned/signed of the field in the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function change_field_unsigned($table, $field, $continue=true, $feedback=true) {

/// Just a wrapper over change_field_type. Does exactly the same processing
    return change_field_type($table, $field, $continue, $feedback);
}

/**
 * This function will change the nullability of the field in the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function change_field_notnull($table, $field, $continue=true, $feedback=true) {

/// Just a wrapper over change_field_type. Does exactly the same processing
    return change_field_type($table, $field, $continue, $feedback);
}

/**
 * This function will change the enum status of the field in the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function change_field_enum($table, $field, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($field)) != 'xmldbfield') {
        return false;
    }

    if(!$sqlarr = $table->getModifyEnumSQL($CFG->dbtype, $CFG->prefix, $field, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}
/**
 * This function will change the default of the field in the table passed as arguments
 * One null value in the default field means delete the default
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField field object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function change_field_default($table, $field, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($field)) != 'xmldbfield') {
        return false;
    }

    if(!$sqlarr = $table->getModifyDefaultSQL($CFG->dbtype, $CFG->prefix, $field, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will rename the field in the table passed as arguments
 * Before renaming the field, the function will check it exists
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBField index object (full specs are required)
 * @param string new name of the field
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function rename_field($table, $field, $newname, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($field)) != 'xmldbfield') {
        return false;
    }

/// Check field isn't id. Renaming over that field is not allowed
    if ($field->getName() == 'id') {
        debugging('Field ' . $field->getName() . ' cannot be renamed. Rename skipped', DEBUG_DEVELOPER);
        return true; //Field is "id", nothing to do
    }

/// Check field exists
    if (!field_exists($table, $field)) {
        debugging('Field ' . $field->getName() . ' do not exist. Rename skipped', DEBUG_DEVELOPER);
        return true; //Field doesn't exist, nothing to do
    }

/// Check newname isn't empty
    if (!$newname) {
        debugging('New name for field ' . $field->getName() . ' is empty! Rename skipped', DEBUG_DEVELOPER);
        return true; //Field doesn't exist, nothing to do
    }

    if(!$sqlarr = $table->getRenameFieldSQL($CFG->dbtype, $CFG->prefix, $field, $newname, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will create the key in the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBKey index object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function add_key($table, $key, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($key)) != 'xmldbkey') {
        return false;
    }
    if ($key->getType() == XMLDB_KEY_PRIMARY) { // Prevent PRIMARY to be added (only in create table, being serious  :-P)
        debugging('Primary Keys can be added at table create time only', DEBUG_DEVELOPER);
        return true;
    }

    if(!$sqlarr = $table->getAddKeySQL($CFG->dbtype, $CFG->prefix, $key, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will drop the key in the table passed as arguments
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBKey key object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function drop_key($table, $key, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($key)) != 'xmldbkey') {
        return false;
    }
    if ($key->getType() == XMLDB_KEY_PRIMARY) { // Prevent PRIMARY to be dropped (only in drop table, being serious  :-P)
        debugging('Primary Keys can be deleted at table drop time only', DEBUG_DEVELOPER);
        return true;
    }

    if(!$sqlarr = $table->getDropKeySQL($CFG->dbtype, $CFG->prefix, $key, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will rename the key in the table passed as arguments
 * Experimental. Shouldn't be used at all in normal installation/upgrade!
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBKey key object (full specs are required)
 * @param string new name of the key
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function rename_key($table, $key, $newname, $continue=true, $feedback=true) {

    global $CFG, $db;

    debugging('rename_key() is one experimental feature. You must not use it in production!', DEBUG_DEVELOPER);

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($key)) != 'xmldbkey') {
        return false;
    }

/// Check newname isn't empty
    if (!$newname) {
        debugging('New name for key ' . $key->getName() . ' is empty! Rename skipped', DEBUG_DEVELOPER);
        return true; //Key doesn't exist, nothing to do
    }

    if(!$sqlarr = $table->getRenameKeySQL($CFG->dbtype, $CFG->prefix, $key, $newname, false)) {
        debugging('Some DBs do not support key renaming (MySQL, PostgreSQL, MsSQL). Rename skipped', DEBUG_DEVELOPER);
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will create the index in the table passed as arguments
 * Before creating the index, the function will check it doesn't exists
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBIndex index object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function add_index($table, $index, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($index)) != 'xmldbindex') {
        return false;
    }

/// Check index doesn't exist
    if (index_exists($table, $index)) {
        debugging('Index ' . $index->getName() . ' exists. Create skipped', DEBUG_DEVELOPER);
        return true; //Index exists, nothing to do
    }

    if(!$sqlarr = $table->getAddIndexSQL($CFG->dbtype, $CFG->prefix, $index, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will drop the index in the table passed as arguments
 * Before dropping the index, the function will check it exists
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBIndex index object (full specs are required)
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function drop_index($table, $index, $continue=true, $feedback=true) {

    global $CFG, $db;

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($index)) != 'xmldbindex') {
        return false;
    }

/// Check index exists
    if (!index_exists($table, $index)) {
        debugging('Index ' . $index->getName() . ' do not exist. Delete skipped', DEBUG_DEVELOPER);
        return true; //Index doesn't exist, nothing to do
    }

    if(!$sqlarr = $table->getDropIndexSQL($CFG->dbtype, $CFG->prefix, $index, false)) {
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/**
 * This function will rename the index in the table passed as arguments
 * Before renaming the index, the function will check it exists
 * Experimental. Shouldn't be used at all!
 *
 * @uses $CFG, $db
 * @param XMLDBTable table object (just the name is mandatory)
 * @param XMLDBIndex index object (full specs are required)
 * @param string new name of the index
 * @param boolean continue to specify if must continue on error (true) or stop (false)
 * @param boolean feedback to specify to show status info (true) or not (false)
 * @return boolean true on success, false on error
 */
function rename_index($table, $index, $newname, $continue=true, $feedback=true) {

    global $CFG, $db;

    debugging('rename_index() is one experimental feature. You must not use it in production!', DEBUG_DEVELOPER);

    $status = true;

    if (strtolower(get_class($table)) != 'xmldbtable') {
        return false;
    }
    if (strtolower(get_class($index)) != 'xmldbindex') {
        return false;
    }

/// Check index exists
    if (!index_exists($table, $index)) {
        debugging('Index ' . $index->getName() . ' do not exist. Rename skipped', DEBUG_DEVELOPER);
        return true; //Index doesn't exist, nothing to do
    }

/// Check newname isn't empty
    if (!$newname) {
        debugging('New name for index ' . $index->getName() . ' is empty! Rename skipped', DEBUG_DEVELOPER);
        return true; //Index doesn't exist, nothing to do
    }

    if(!$sqlarr = $table->getRenameIndexSQL($CFG->dbtype, $CFG->prefix, $index, $newname, false)) {
        debugging('Some DBs do not support index renaming (MySQL). Rename skipped', DEBUG_DEVELOPER);
        return true; //Empty array = nothing to do = no error
    }

    return execute_sql_arr($sqlarr, $continue, $feedback);
}

/* trys to change default db encoding to utf8, if empty db
 */
function change_db_encoding() {
    global $CFG, $db;  
    // try forcing utf8 collation, if mysql db and no tables present
    if (($CFG->dbtype=='mysql') && !$db->Metatables()) {
        $SQL = 'ALTER DATABASE '.$CFG->dbname.' CHARACTER SET utf8';
        execute_sql($SQL, false); // silent, if it fails it fails
        if (setup_is_unicodedb()) {
            configure_dbconnection();   
        }
    }
}

?>