gnu-social/lib/schema.php

<?php
/**
 * StatusNet, the distributed open-source microblogging tool
 *
 * Database schema utilities
 *
 * PHP version 5
 *
 * LICENCE: This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @category  Database
 * @package   StatusNet
 * @author    Evan Prodromou <evan@status.net>
 * @copyright 2009 StatusNet, Inc.
 * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
 * @link      http://status.net/
 */

if (!defined('STATUSNET')) {
    exit(1);
}

/**
 * Class representing the database schema
 *
 * A class representing the database schema. Can be used to
 * manipulate the schema -- especially for plugins and upgrade
 * utilities.
 *
 * @category Database
 * @package  StatusNet
 * @author   Evan Prodromou <evan@status.net>
 * @author   Brion Vibber <brion@status.net>
 * @license  http://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
 * @link     http://status.net/
 */

class Schema
{
    static $_static = null;
    protected $conn = null;

    /**
     * Constructor. Only run once for singleton object.
     */

    protected function __construct($conn = null)
    {
        if (is_null($conn)) {
            // XXX: there should be an easier way to do this.
            $user = new User();
            $conn = $user->getDatabaseConnection();
            $user->free();
            unset($user);
        }

        $this->conn = $conn;
    }

    /**
     * Main public entry point. Use this to get
     * the schema object.
     *
     * @return Schema the Schema object for the connection
     */

    static function get($conn = null)
    {
        if (is_null($conn)) {
            $key = 'default';
        } else {
            $key = md5(serialize($conn->dsn));
        }
        
        $type = common_config('db', 'type');
        if (empty(self::$_static[$key])) {
            $schemaClass = ucfirst($type).'Schema';
            self::$_static[$key] = new $schemaClass($conn);
        }
        return self::$_static[$key];
    }

    /**
     * Gets a ColumnDef object for a single column.
     *
     * Throws an exception if the table is not found.
     *
     * @param string $table  name of the table
     * @param string $column name of the column
     *
     * @return ColumnDef definition of the column or null
     *                   if not found.
     */

    public function getColumnDef($table, $column)
    {
        $td = $this->getTableDef($table);

        if (!empty($td) && !empty($td->columns)) {
            foreach ($td->columns as $cd) {
                if ($cd->name == $column) {
                    return $cd;
                }
            }
        }

        return null;
    }

    /**
     * Creates a table with the given names and columns.
     *
     * @param string $tableName    Name of the table
     * @param array  $def          Table definition array listing fields and indexes.
     *
     * @return boolean success flag
     */

    public function createTable($tableName, $def)
    {
        $statements = $this->buildCreateTable($tableName, $def);
        return $this->runSqlSet($statements);
    }

    /**
     * Build a set of SQL statements to create a table with the given
     * name and columns.
     *
     * @param string $name    Name of the table
     * @param array  $def     Table definition array
     *
     * @return boolean success flag
     */
    public function buildCreateTable($name, $def)
    {
        $def = $this->validateDef($name, $def);
        $def = $this->filterDef($def);
        $sql = array();

        foreach ($def['fields'] as $col => $colDef) {
            $this->appendColumnDef($sql, $col, $colDef);
        }

        // Primary, unique, and foreign keys are constraints, so go within
        // the CREATE TABLE statement normally.
        if (!empty($def['primary key'])) {
            $this->appendPrimaryKeyDef($sql, $def['primary key']);
        }

        if (!empty($def['unique keys'])) {
            foreach ($def['unique keys'] as $col => $colDef) {
                $this->appendUniqueKeyDef($sql, $col, $colDef);
            }
        }

        if (!empty($def['foreign keys'])) {
            foreach ($def['foreign keys'] as $keyName => $keyDef) {
                $this->appendForeignKeyDef($sql, $keyName, $keyDef);
            }
        }

        // Wrap the CREATE TABLE around the main body chunks...
        $statements = array();
        $statements[] = $this->startCreateTable($name, $def) . "\n" .
                        implode($sql, ",\n") . "\n" .
                        $this->endCreateTable($name, $def);

        // Multi-value indexes are advisory and for best portability
        // should be created as separate statements.
        if (!empty($def['indexes'])) {
            foreach ($def['indexes'] as $col => $colDef) {
                $this->appendCreateIndex($statements, $name, $col, $colDef);
            }
        }
        if (!empty($def['fulltext indexes'])) {
            foreach ($def['fulltext indexes'] as $col => $colDef) {
                $this->appendCreateFulltextIndex($statements, $name, $col, $colDef);
            }
        }

        return $statements;
    }

    /**
     * Set up a 'create table' SQL statement.
     *
     * @param string $name table name
     * @param array $def table definition
     * @param $string
     */
    function startCreateTable($name, array $def)
    {
        return 'CREATE TABLE ' . $this->quoteIdentifier($name)  . ' (';
    }

    /**
     * Close out a 'create table' SQL statement.
     *
     * @param string $name table name
     * @param array $def table definition
     * @return string
     */
    function endCreateTable($name, array $def)
    {
        return ')';
    }

    /**
     * Append an SQL fragment with a column definition in a CREATE TABLE statement.
     *
     * @param array $sql
     * @param string $name
     * @param array $def
     */
    function appendColumnDef(array &$sql, $name, array $def)
    {
        $sql[] = "$name " . $this->columnSql($def);
    }

    /**
     * Append an SQL fragment with a constraint definition for a primary
     * key in a CREATE TABLE statement.
     *
     * @param array $sql
     * @param array $def
     */
    function appendPrimaryKeyDef(array &$sql, array $def)
    {
        $sql[] = "PRIMARY KEY " . $this->buildIndexList($def);
    }

    /**
     * Append an SQL fragment with a constraint definition for a unique
     * key in a CREATE TABLE statement.
     *
     * @param array $sql
     * @param string $name
     * @param array $def
     */
    function appendUniqueKeyDef(array &$sql, $name, array $def)
    {
        $sql[] = "CONSTRAINT $name UNIQUE " . $this->buildIndexList($def);
    }

    /**
     * Append an SQL fragment with a constraint definition for a foreign
     * key in a CREATE TABLE statement.
     *
     * @param array $sql
     * @param string $name
     * @param array $def
     */
    function appendForeignKeyDef(array &$sql, $name, array $def)
    {
        if (count($def) != 2) {
            throw new Exception("Invalid foreign key def for $name: " . var_export($def, true));
        }
        list($refTable, $map) = $def;
        $srcCols = array_keys($map);
        $refCols = array_values($map);
        $sql[] = "CONSTRAINT $name FOREIGN KEY " .
                 $this->buildIndexList($srcCols) .
                 " REFERENCES " .
                 $this->quoteIdentifier($refTable) .
                 " " .
                 $this->buildIndexList($refCols);
    }

    /**
     * Append an SQL statement with an index definition for an advisory
     * index over one or more columns on a table.
     *
     * @param array $statements
     * @param string $table
     * @param string $name
     * @param array $def
     */
    function appendCreateIndex(array &$statements, $table, $name, array $def)
    {
        $statements[] = "CREATE INDEX $name ON $table " . $this->buildIndexList($def);
    }

    /**
     * Append an SQL statement with an index definition for a full-text search
     * index over one or more columns on a table.
     *
     * @param array $statements
     * @param string $table
     * @param string $name
     * @param array $def
     */
    function appendCreateFulltextIndex(array &$statements, $table, $name, array $def)
    {
        throw new Exception("Fulltext index not supported in this database");
    }

    /**
     * Append an SQL statement to drop an index from a table.
     *
     * @param array $statements
     * @param string $table
     * @param string $name
     * @param array $def
     */
    function appendDropIndex(array &$statements, $table, $name)
    {
        $statements[] = "DROP INDEX $name ON " . $this->quoteIdentifier($table);
    }

    function buildIndexList(array $def)
    {
        // @fixme
        return '(' . implode(',', array_map(array($this, 'buildIndexItem'), $def)) . ')';
    }

    function buildIndexItem($def)
    {
        if (is_array($def)) {
            list($name, $size) = $def;
            return $this->quoteIdentifier($name) . '(' . intval($size) . ')';
        }
        return $this->quoteIdentifier($def);
    }

    /**
     * Drops a table from the schema
     *
     * Throws an exception if the table is not found.
     *
     * @param string $name Name of the table to drop
     *
     * @return boolean success flag
     */

    public function dropTable($name)
    {
        $res = $this->conn->query("DROP TABLE $name");

        if (PEAR::isError($res)) {
            throw new Exception($res->getMessage());
        }

        return true;
    }

    /**
     * Adds an index to a table.
     *
     * If no name is provided, a name will be made up based
     * on the table name and column names.
     *
     * Throws an exception on database error, esp. if the table
     * does not exist.
     *
     * @param string $table       Name of the table
     * @param array  $columnNames Name of columns to index
     * @param string $name        (Optional) name of the index
     *
     * @return boolean success flag
     */

    public function createIndex($table, $columnNames, $name=null)
    {
        if (!is_array($columnNames)) {
            $columnNames = array($columnNames);
        }

        if (empty($name)) {
            $name = "{$table}_".implode("_", $columnNames)."_idx";
        }

        $res = $this->conn->query("ALTER TABLE $table ".
                                   "ADD INDEX $name (".
                                   implode(",", $columnNames).")");

        if (PEAR::isError($res)) {
            throw new Exception($res->getMessage());
        }

        return true;
    }

    /**
     * Drops a named index from a table.
     *
     * @param string $table name of the table the index is on.
     * @param string $name  name of the index
     *
     * @return boolean success flag
     */

    public function dropIndex($table, $name)
    {
        $res = $this->conn->query("ALTER TABLE $table DROP INDEX $name");

        if (PEAR::isError($res)) {
            throw new Exception($res->getMessage());
        }

        return true;
    }

    /**
     * Adds a column to a table
     *
     * @param string    $table     name of the table
     * @param ColumnDef $columndef Definition of the new
     *                             column.
     *
     * @return boolean success flag
     */

    public function addColumn($table, $columndef)
    {
        $sql = "ALTER TABLE $table ADD COLUMN " . $this->_columnSql($columndef);

        $res = $this->conn->query($sql);

        if (PEAR::isError($res)) {
            throw new Exception($res->getMessage());
        }

        return true;
    }

    /**
     * Modifies a column in the schema.
     *
     * The name must match an existing column and table.
     *
     * @param string    $table     name of the table
     * @param ColumnDef $columndef new definition of the column.
     *
     * @return boolean success flag
     */

    public function modifyColumn($table, $columndef)
    {
        $sql = "ALTER TABLE $table MODIFY COLUMN " .
          $this->_columnSql($columndef);

        $res = $this->conn->query($sql);

        if (PEAR::isError($res)) {
            throw new Exception($res->getMessage());
        }

        return true;
    }

    /**
     * Drops a column from a table
     *
     * The name must match an existing column.
     *
     * @param string $table      name of the table
     * @param string $columnName name of the column to drop
     *
     * @return boolean success flag
     */

    public function dropColumn($table, $columnName)
    {
        $sql = "ALTER TABLE $table DROP COLUMN $columnName";

        $res = $this->conn->query($sql);

        if (PEAR::isError($res)) {
            throw new Exception($res->getMessage());
        }

        return true;
    }

    /**
     * Ensures that a table exists with the given
     * name and the given column definitions.
     *
     * If the table does not yet exist, it will
     * create the table. If it does exist, it will
     * alter the table to match the column definitions.
     *
     * @param string $tableName name of the table
     * @param array  $def       Table definition array
     *
     * @return boolean success flag
     */

    public function ensureTable($tableName, $def)
    {
        $statements = $this->buildEnsureTable($tableName, $def);
        return $this->runSqlSet($statements);
    }

    /**
     * Run a given set of SQL commands on the connection in sequence.
     * Empty input is ok.
     *
     * @fixme if multiple statements, wrap in a transaction?
     * @param array $statements
     * @return boolean success flag
     */
    function runSqlSet(array $statements)
    {
        $ok = true;
        foreach ($statements as $sql) {
            if (defined('DEBUG_INSTALLER')) {
                echo "<tt>" . htmlspecialchars($sql) . "</tt><br/>\n";
            }
            $res = $this->conn->query($sql);

            if (PEAR::isError($res)) {
                throw new Exception($res->getMessage());
            }
        }
        return $ok;
    }

    /**
     * Check a table's status, and if needed build a set
     * of SQL statements which change it to be consistent
     * with the given table definition.
     *
     * If the table does not yet exist, statements will
     * be returned to create the table. If it does exist,
     * statements will be returned to alter the table to
     * match the column definitions.
     *
     * @param string $tableName name of the table
     * @param array  $columns   array of ColumnDef
     *                          objects for the table
     *
     * @return array of SQL statements
     */

    function buildEnsureTable($tableName, array $def)
    {
        try {
            $old = $this->getTableDef($tableName);
        } catch (SchemaTableMissingException $e) {
            return $this->buildCreateTable($tableName, $def);
        }

        // Filter the DB-independent table definition to match the current
        // database engine's features and limitations.
        $def = $this->validateDef($tableName, $def);
        $def = $this->filterDef($def);

        $statements = array();
        $fields = $this->diffArrays($old, $def, 'fields', array($this, 'columnsEqual'));
        $uniques = $this->diffArrays($old, $def, 'unique keys');
        $indexes = $this->diffArrays($old, $def, 'indexes');
        $foreign = $this->diffArrays($old, $def, 'foreign keys');

        // Drop any obsolete or modified indexes ahead...
        foreach ($indexes['del'] + $indexes['mod'] as $indexName) {
            $this->appendDropIndex($statements, $tableName, $indexName);
        }

        // For efficiency, we want this all in one
        // query, instead of using our methods.

        $phrase = array();

        foreach ($foreign['del'] + $foreign['mod'] as $keyName) {
            $this->appendAlterDropForeign($phrase, $keyName);
        }

        foreach ($uniques['del'] + $uniques['mod'] as $keyName) {
            $this->appendAlterDropUnique($phrase, $keyName);
        }

        if (isset($old['primary key']) && (!isset($def['primary key']) || $def['primary key'] != $old['primary key'])) {
            $this->appendAlterDropPrimary($phrase);
        }

        foreach ($fields['add'] as $columnName) {
            $this->appendAlterAddColumn($phrase, $columnName,
                    $def['fields'][$columnName]);
        }

        foreach ($fields['mod'] as $columnName) {
            $this->appendAlterModifyColumn($phrase, $columnName,
                    $old['fields'][$columnName],
                    $def['fields'][$columnName]);
        }

        foreach ($fields['del'] as $columnName) {
            $this->appendAlterDropColumn($phrase, $columnName);
        }

        if (isset($def['primary key']) && (!isset($old['primary key']) || $old['primary key'] != $def['primary key'])) {
            $this->appendAlterAddPrimary($phrase, $def['primary key']);
        }

        foreach ($uniques['mod'] + $uniques['add'] as $keyName) {
            $this->appendAlterAddUnique($phrase, $keyName, $def['unique keys'][$keyName]);
        }

        foreach ($foreign['mod'] + $foreign['add'] as $keyName) {
            $this->appendAlterAddForeign($phrase, $keyName, $def['foreign keys'][$keyName]);
        }

        $this->appendAlterExtras($phrase, $tableName, $def);

        if (count($phrase) > 0) {
            $sql = 'ALTER TABLE ' . $tableName . ' ' . implode(",\n", $phrase);
            $statements[] = $sql;
        }

        // Now create any indexes...
        foreach ($indexes['mod'] + $indexes['add'] as $indexName) {
            $this->appendCreateIndex($statements, $tableName, $indexName, $def['indexes'][$indexName]);
        }

        return $statements;
    }

    function diffArrays($oldDef, $newDef, $section, $compareCallback=null)
    {
        $old = isset($oldDef[$section]) ? $oldDef[$section] : array();
        $new = isset($newDef[$section]) ? $newDef[$section] : array();

        $oldKeys = array_keys($old);
        $newKeys = array_keys($new);

        $toadd  = array_diff($newKeys, $oldKeys);
        $todrop = array_diff($oldKeys, $newKeys);
        $same   = array_intersect($newKeys, $oldKeys);
        $tomod  = array();
        $tokeep = array();

        // Find which fields have actually changed definition
        // in a way that we need to tweak them for this DB type.
        foreach ($same as $name) {
            if ($compareCallback) {
                $same = call_user_func($compareCallback, $old[$name], $new[$name]);
            } else {
                $same = ($old[$name] == $new[$name]);
            }
            if ($same) {
                $tokeep[] = $name;
                continue;
            }
            $tomod[] = $name;
        }
        return array('add' => $toadd,
                     'del' => $todrop,
                     'mod' => $tomod,
                     'keep' => $tokeep,
                     'count' => count($toadd) + count($todrop) + count($tomod));
    }

    /**
     * Append phrase(s) to an array of partial ALTER TABLE chunks in order
     * to add the given column definition to the table.
     *
     * @param array $phrase
     * @param string $columnName
     * @param array $cd 
     */
    function appendAlterAddColumn(array &$phrase, $columnName, array $cd)
    {
        $phrase[] = 'ADD COLUMN ' .
                    $this->quoteIdentifier($columnName) .
                    ' ' .
                    $this->columnSql($cd);
    }

    /**
     * Append phrase(s) to an array of partial ALTER TABLE chunks in order
     * to alter the given column from its old state to a new one.
     *
     * @param array $phrase
     * @param string $columnName
     * @param array $old previous column definition as found in DB
     * @param array $cd current column definition
     */
    function appendAlterModifyColumn(array &$phrase, $columnName, array $old, array $cd)
    {
        $phrase[] = 'MODIFY COLUMN ' .
                    $this->quoteIdentifier($columnName) .
                    ' ' .
                    $this->columnSql($cd);
    }

    /**
     * Append phrase(s) to an array of partial ALTER TABLE chunks in order
     * to drop the given column definition from the table.
     *
     * @param array $phrase
     * @param string $columnName
     */
    function appendAlterDropColumn(array &$phrase, $columnName)
    {
        $phrase[] = 'DROP COLUMN ' . $this->quoteIdentifier($columnName);
    }

    function appendAlterAddUnique(array &$phrase, $keyName, array $def)
    {
        $sql = array();
        $sql[] = 'ADD';
        $this->appendUniqueKeyDef($sql, $keyName, $def);
        $phrase[] = implode(' ', $sql);
    }

    function appendAlterAddForeign(array &$phrase, $keyName, array $def)
    {
        $sql = array();
        $sql[] = 'ADD';
        $this->appendForeignKeyDef($sql, $keyName, $def);
        $phrase[] = implode(' ', $sql);
    }

    function appendAlterAddPrimary(array &$phrase, array $def)
    {
        $sql = array();
        $sql[] = 'ADD';
        $this->appendPrimaryKeyDef($sql, $def);
        $phrase[] = implode(' ', $sql);
    }

    function appendAlterDropPrimary(array &$phrase)
    {
        $phrase[] = 'DROP CONSTRAINT PRIMARY KEY';
    }

    function appendAlterDropUnique(array &$phrase, $keyName)
    {
        $phrase[] = 'DROP CONSTRAINT ' . $keyName;
    }

    function appendAlterDropForeign(array &$phrase, $keyName)
    {
        $phrase[] = 'DROP FOREIGN KEY ' . $keyName;
    }

    function appendAlterExtras(array &$phrase, $tableName, array $def)
    {
        // no-op
    }

    /**
     * Quote a db/table/column identifier if necessary.
     *
     * @param string $name
     * @return string
     */
    function quoteIdentifier($name)
    {
        return $name;
    }

    function quoteDefaultValue($cd)
    {
        if ($cd['type'] == 'datetime' && $cd['default'] == 'CURRENT_TIMESTAMP') {
            return $cd['default'];
        } else {
            return $this->quoteValue($cd['default']);
        }
    }

    function quoteValue($val)
    {
        return $this->conn->quoteSmart($val);
    }

    /**
     * Check if two column definitions are equivalent.
     * The default implementation checks _everything_ but in many cases
     * you may be able to discard a bunch of equivalencies.
     *
     * @param array $a
     * @param array $b
     * @return boolean
     */
    function columnsEqual(array $a, array $b)
    {
        return !array_diff_assoc($a, $b) && !array_diff_assoc($b, $a);
    }

    /**
     * Returns the array of names from an array of
     * ColumnDef objects.
     *
     * @param array $cds array of ColumnDef objects
     *
     * @return array strings for name values
     */

    protected function _names($cds)
    {
        $names = array();

        foreach ($cds as $cd) {
            $names[] = $cd->name;
        }

        return $names;
    }

    /**
     * Get a ColumnDef from an array matching
     * name.
     *
     * @param array  $cds  Array of ColumnDef objects
     * @param string $name Name of the column
     *
     * @return ColumnDef matching item or null if no match.
     */

    protected function _byName($cds, $name)
    {
        foreach ($cds as $cd) {
            if ($cd->name == $name) {
                return $cd;
            }
        }

        return null;
    }

    /**
     * Return the proper SQL for creating or
     * altering a column.
     *
     * Appropriate for use in CREATE TABLE or
     * ALTER TABLE statements.
     *
     * @param ColumnDef $cd column to create
     *
     * @return string correct SQL for that column
     */

    function columnSql(array $cd)
    {
        $line = array();
        $line[] = $this->typeAndSize($cd);

        if (isset($cd['default'])) {
            $line[] = 'default';
            $line[] = $this->quoteDefaultValue($cd);
        } else if (!empty($cd['not null'])) {
            // Can't have both not null AND default!
            $line[] = 'not null';
        }

        return implode(' ', $line);
    }

    /**
     *
     * @param string $column canonical type name in defs
     * @return string native DB type name
     */
    function mapType($column)
    {
        return $column;
    }

    function typeAndSize($column)
    {
        //$type = $this->mapType($column);
        $type = $column['type'];
        if (isset($column['size'])) {
            $type = $column['size'] . $type;
        }
        $lengths = array();

        if (isset($column['precision'])) {
            $lengths[] = $column['precision'];
            if (isset($column['scale'])) {
                $lengths[] = $column['scale'];
            }
        } else if (isset($column['length'])) {
            $lengths[] = $column['length'];
        }

        if ($lengths) {
            return $type . '(' . implode(',', $lengths) . ')';
        } else {
            return $type;
        }
    }

    /**
     * Convert an old-style set of ColumnDef objects into the current
     * Drupal-style schema definition array, for backwards compatibility
     * with plugins written for 0.9.x.
     *
     * @param string $tableName
     * @param array $defs: array of ColumnDef objects
     * @return array
     */
    protected function oldToNew($tableName, array $defs)
    {
        $table = array();
        $prefixes = array(
            'tiny',
            'small',
            'medium',
            'big',
        );
        foreach ($defs as $cd) {
            $column = array();
            $column['type'] = $cd->type;
            foreach ($prefixes as $prefix) {
                if (substr($cd->type, 0, strlen($prefix)) == $prefix) {
                    $column['type'] = substr($cd->type, strlen($prefix));
                    $column['size'] = $prefix;
                    break;
                }
            }

            if ($cd->size) {
                if ($cd->type == 'varchar' || $cd->type == 'char') {
                    $column['length'] = $cd->size;
                }
            }
            if (!$cd->nullable) {
                $column['not null'] = true;
            }
            if ($cd->auto_increment) {
                $column['type'] = 'serial';
            }
            if ($cd->default) {
                $column['default'] = $cd->default;
            }
            $table['fields'][$cd->name] = $column;

            if ($cd->key == 'PRI') {
                // If multiple columns are defined as primary key,
                // we'll pile them on in sequence.
                if (!isset($table['primary key'])) {
                    $table['primary key'] = array();
                }
                $table['primary key'][] = $cd->name;
            } else if ($cd->key == 'MUL') {
                // Individual multiple-value indexes are only per-column
                // using the old ColumnDef syntax.
                $idx = "{$tableName}_{$cd->name}_idx";
                $table['indexes'][$idx] = array($cd->name);
            } else if ($cd->key == 'UNI') {
                // Individual unique-value indexes are only per-column
                // using the old ColumnDef syntax.
                $idx = "{$tableName}_{$cd->name}_idx";
                $table['unique keys'][$idx] = array($cd->name);
            }
        }

        return $table;
    }

    /**
     * Filter the given table definition array to match features available
     * in this database.
     *
     * This lets us strip out unsupported things like comments, foreign keys,
     * or type variants that we wouldn't get back from getTableDef().
     *
     * @param array $tableDef
     */
    function filterDef(array $tableDef)
    {
        return $tableDef;
    }

    /**
     * Validate a table definition array, checking for basic structure.
     *
     * If necessary, converts from an old-style array of ColumnDef objects.
     *
     * @param string $tableName
     * @param array $def: table definition array
     * @return array validated table definition array
     *
     * @throws Exception on wildly invalid input
     */
    function validateDef($tableName, array $def)
    {
        if (isset($def[0]) && $def[0] instanceof ColumnDef) {
            $def = $this->oldToNew($tableName, $def);
        }

        // A few quick checks :D
        if (!isset($def['fields'])) {
            throw new Exception("Invalid table definition for $tableName: no fields.");
        }

        return $def;
    }

    function isNumericType($type)
    {
        $type = strtolower($type);
        $known = array('int', 'serial', 'numeric');
        return in_array($type, $known);
    }

    /**
     * Pull info from the query into a fun-fun array of dooooom
     *
     * @param string $sql
     * @return array of arrays
     */
    protected function fetchQueryData($sql)
    {
        $res = $this->conn->query($sql);
        if (PEAR::isError($res)) {
            throw new Exception($res->getMessage());
        }

        $out = array();
        $row = array();
        while ($res->fetchInto($row, DB_FETCHMODE_ASSOC)) {
            $out[] = $row;
        }
        $res->free();

        return $out;
    }

}

class SchemaTableMissingException extends Exception
{
    // no-op
}