class.orm.php

<?php
/*********************************************************************
    class.orm.php

    Simple ORM (Object Relational Mapper) for PHP5 based on Django's ORM,
    except that complex filter operations are not supported. The ORM simply
    supports ANDed filter operations without any GROUP BY support.

    Jared Hancock <jared@osticket.com>
    Copyright (c)  2006-2013 osTicket
    http://www.osticket.com

    Released under the GNU General Public License WITHOUT ANY WARRANTY.
    See LICENSE.TXT for details.

    vim: expandtab sw=4 ts=4 sts=4:
**********************************************************************/

class OrmException extends Exception {}
class OrmConfigurationException extends Exception {}

/**
 * Meta information about a model including edges (relationships), table
 * name, default sorting information, database fields, etc.
 *
 * This class is constructed and built automatically from the model's
 * ::_inspect method using a class's ::$meta array.
 */
class ModelMeta implements ArrayAccess {

    var $base = array();
    var $model;

    function __construct($model) {
        $this->model = $model;
        $meta = $model::$meta;

        // TODO: Merge ModelMeta from parent model (if inherited)

        if (!$meta['table'])
            throw new OrmConfigurationException(
                __('Model does not define meta.table'), $model);
        elseif (!$meta['pk'])
            throw new OrmConfigurationException(
                __('Model does not define meta.pk'), $model);

        // Ensure other supported fields are set and are arrays
        foreach (array('pk', 'ordering', 'deferred') as $f) {
            if (!isset($meta[$f]))
                $meta[$f] = array();
            elseif (!is_array($meta[$f]))
                $meta[$f] = array($meta[$f]);
        }

        // Break down foreign-key metadata
        if (!isset($meta['joins']))
            $meta['joins'] = array();
        foreach ($meta['joins'] as $field => &$j) {
            if (isset($j['reverse'])) {
                list($model, $key) = explode('.', $j['reverse']);
                $info = $model::$meta['joins'][$key];
                $constraint = array();
                if (!is_array($info['constraint']))
                    throw new OrmConfigurationException(sprintf(__(
                        // `reverse` here is the reverse of an ORM relationship
                        '%s: Reverse does not specify any constraints'),
                        $j['reverse']));
                foreach ($info['constraint'] as $foreign => $local) {
                    list(,$field) = explode('.', $local);
                    $constraint[$field] = "$model.$foreign";
                }
                $j['constraint'] = $constraint;
                if (!isset($j['list']))
                    $j['list'] = true;
            }
            // XXX: Make this better (ie. composite keys)
            $keys = array_keys($j['constraint']);
            $foreign = $j['constraint'][$keys[0]];
            $j['fkey'] = explode('.', $foreign);
            $j['local'] = $keys[0];
        }
        $this->base = $meta;
    }

    function offsetGet($field) {
        if (!isset($this->base[$field]))
            $this->setupLazy($field);
        return $this->base[$field];
    }
    function offsetSet($field, $what) {
        $this->base[$field] = $what;
    }
    function offsetExists($field) {
        return isset($this->base[$field]);
    }
    function offsetUnset($field) {
        throw new Exception('Model MetaData is immutable');
    }

    function setupLazy($what) {
        switch ($what) {
        case 'fields':
            $this->base['fields'] = self::inspectFields();
            break;
        case 'newInstance':
            $class_repr = sprintf(
                'O:%d:"%s":0:{}',
                strlen($this->model), $this->model
            );
            $this->base['newInstance'] = function() use ($class_repr) {
                return unserialize($class_repr);
            };
            break;
        default:
            throw new Exception($what . ': No such meta-data');
        }
    }

    function inspectFields() {
        return DbEngine::getCompiler()->inspectTable($this['table']);
    }
}

class VerySimpleModel {
    static $meta = array(
        'table' => false,
        'ordering' => false,
        'pk' => false
    );

    var $ht;
    var $dirty = array();
    var $__new__ = false;
    var $__deleted__ = false;
    var $__deferred__ = array();

    function __construct($row) {
        $this->ht = $row;
    }

    function get($field, $default=false) {
        if (array_key_exists($field, $this->ht))
            return $this->ht[$field];
        elseif (isset(static::$meta['joins'][$field])) {
            // Make sure joins were inspected
            if (!static::$meta instanceof ModelMeta)
                static::_inspect();
            $j = static::$meta['joins'][$field];
            // Support instrumented lists and such
            if (isset($this->ht[$j['local']])
                    && isset($j['list']) && $j['list']) {
                $fkey = $j['fkey'];
                $v = $this->ht[$name] = new InstrumentedList(
                    // Send Model, Foriegn-Field, Local-Id
                    array($fkey[0], $fkey[1], $this->get($j['local']))
                );
                return $v;
            }
            // Support relationships
            elseif (isset($j['fkey'])
                    && ($class = $j['fkey'][0])
                    && class_exists($class)) {
                $v = $this->ht[$field] = $class::lookup(
                    array($j['fkey'][1] => $this->ht[$j['local']]));
                return $v;
            }
        }
        elseif (isset($this->__deferred__[$field])) {
            // Fetch deferred field
            $row = static::objects()->filter($this->getPk())
                ->values_flat($field)
                ->one();
            if ($row)
                return $this->ht[$field] = $row[0];
        }
        elseif ($field == 'pk') {
            return $this->getPk();
        }

        if (isset($default))
            return $default;
        // TODO: Inspect fields from database before throwing this error
        throw new OrmException(sprintf(__('%s: %s: Field not defined'),
            get_class($this), $field));
    }
    function __get($field) {
        return $this->get($field, null);
    }

    function __isset($field) {
        return array_key_exists($field, $this->ht)
            || isset(static::$meta['joins'][$field]);
    }
    function __unset($field) {
        unset($this->ht[$field]);
    }

    function set($field, $value) {
        // Update of foreign-key by assignment to model instance
        if (isset(static::$meta['joins'][$field])) {
            $j = static::$meta['joins'][$field];
            if ($j['list'] && ($value instanceof InstrumentedList)) {
                // Magic list property
                $this->ht[$field] = $value;
                return;
            }
            if ($value === null) {
                // Pass. Set local field to NULL in logic below
            }
            elseif ($value instanceof $j['fkey'][0]) {
                if ($value->__new__)
                    $value->save();
                // Capture the object under the object's field name
                $this->ht[$field] = $value;
                $value = $value->get($j['fkey'][1]);
                // Fall through to the standard logic below
            }
            else
                throw new InvalidArgumentException(
                    sprintf(__('Expecting NULL or instance of %s'), $j['fkey'][0]));

            // Capture the foreign key id value
            $field = $j['local'];
        }
        // XXX: Fully support or die if updating pk
        // XXX: The contents of $this->dirty should be the value after the
        // previous fetch or save. For instance, if the value is changed more
        // than once, the original value should be preserved in the dirty list
        // on the second edit.
        $old = isset($this->ht[$field]) ? $this->ht[$field] : null;
        if ($old != $value) {
            $this->dirty[$field] = $old;
            $this->ht[$field] = $value;
        }
    }
    function __set($field, $value) {
        return $this->set($field, $value);
    }

    function setAll($props) {
        foreach ($props as $field=>$value)
            $this->set($field, $value);
    }

    function __onload() {}
    static function __oninspect() {}

    static function _inspect() {
        if (!static::$meta instanceof ModelMeta) {
            static::$meta = new ModelMeta(get_called_class());

            // Let the model participate
            static::__oninspect();
        }
    }

    /**
     * objects
     *
     * Retrieve a QuerySet for this model class which can be used to fetch
     * models from the connected database. Subclasses can override this
     * method to apply forced constraints on the QuerySet.
     */
    static function objects() {
        return new QuerySet(get_called_class());
    }

    /**
     * lookup
     *
     * Retrieve a record by its primary key. This method may be short
     * circuited by model caching if the record has already been loaded by
     * the database. In such a case, the database will not be consulted for
     * the model's data.
     *
     * This method can be called with an array of keyword arguments matching
     * the PK of the object or the values of the primary key. Both of these
     * usages are correct:
     *
     * >>> User::lookup(1)
     * >>> User::lookup(array('id'=>1))
     *
     * For composite primary keys and the first usage, pass the values in
     * the order they are given in the Model's 'pk' declaration in its meta
     * data.
     *
     * Parameters:
     * $criteria - (mixed) primary key for the sought model either as
     *      arguments or key/value array as the function's first argument
     */
    static function lookup($criteria) {
        // Model::lookup(1), where >1< is the pk value
        if (!is_array($criteria)) {
            $criteria = array();
            foreach (func_get_args() as $i=>$f)
                $criteria[static::$meta['pk'][$i]] = $f;
        }
        if ($cached = ModelInstanceManager::checkCache(get_called_class(),
                $criteria))
            return $cached;
        return static::objects()->filter($criteria)->one();
    }

    function delete($pk=false) {
        $ex = DbEngine::delete($this);
        try {
            $ex->execute();
            if ($ex->affected_rows() != 1)
                return false;

            $this->__deleted__ = true;
            Signal::send('model.deleted', $this);
        }
        catch (OrmException $e) {
            return false;
        }
        return true;
    }

    function save($refetch=false) {
        if (count($this->dirty) === 0)
            return true;

        $ex = DbEngine::save($this);
        try {
            $ex->execute();
            if ($ex->affected_rows() != 1)
                return false;
        }
        catch (OrmException $e) {
            return false;
        }

        $pk = static::$meta['pk'];

        if ($this->__new__) {
            if (count($pk) == 1)
                // XXX: Ensure AUTO_INCREMENT is set for the field
                $this->ht[$pk[0]] = $ex->insert_id();
            $this->__new__ = false;
            Signal::send('model.created', $this);
        }
        else {
            $data = array('dirty' => $this->dirty);
            Signal::send('model.updated', $this, $data);
        }
        # Refetch row from database
        # XXX: Too much voodoo
        if ($refetch) {
            // Uncache so that the lookup will not be short-cirtuited to
            // return this object
            ModelInstanceManager::uncache($this);
            $self = static::lookup($this->get('pk'));
            $this->ht = $self->ht;
        }
        $this->dirty = array();
        return $this->get($pk[0]);
    }

    static function create($ht=false) {
        if (!$ht) $ht=array();
        $class = get_called_class();
        $i = new $class(array());
        $i->__new__ = true;
        foreach ($ht as $field=>$value)
            if (!is_array($value))
                $i->set($field, $value);
        return $i;
    }

    private function getPk() {
        $pk = array();
        foreach ($this::$meta['pk'] as $f)
            $pk[$f] = $this->ht[$f];
        return $pk;
    }
}

class SqlFunction {
    function SqlFunction($name) {
        $this->func = $name;
        $this->args = array_slice(func_get_args(), 1);
    }

    function toSql($compiler=false) {
        $args = (count($this->args)) ? implode(',', db_input($this->args)) : "";
        return sprintf('%s(%s)', $this->func, $args);
    }

    static function __callStatic($func, $args) {
        $I = new static($func);
        $I->args = $args;
        return $I;
    }
}

class QuerySet implements IteratorAggregate, ArrayAccess {
    var $model;

    var $constraints = array();
    var $ordering = array();
    var $limit = false;
    var $offset = 0;
    var $related = array();
    var $values = array();
    var $defer = array();
    var $lock = false;

    const LOCK_EXCLUSIVE = 1;
    const LOCK_SHARED = 2;

    var $compiler = 'MySqlCompiler';
    var $iterator = 'ModelInstanceManager';

    var $params;
    var $query;

    function __construct($model) {
        $this->model = $model;
    }

    function filter() {
        // Multiple arrays passes means OR
        $filter = array();
        foreach (func_get_args() as $Q) {
            $filter[] = $Q instanceof Q ? $Q : new Q($Q);
        }
        $this->constraints[] = new Q($filter, Q::ANY);
        return $this;
    }

    function exclude() {
        $filter = array();
        foreach (func_get_args() as $Q) {
            $filter[] = $Q instanceof Q ? $Q->negate() : Q::not($Q);
        }
        $this->constraints[] = new Q($filter, Q::ANY);
        return $this;
    }

    function defer() {
        foreach (func_get_args() as $f)
            $this->defer[$f] = true;
        return $this;
    }

    function order_by() {
        $this->ordering = array_merge($this->ordering, func_get_args());
        return $this;
    }

    function lock($how=false) {
        $this->lock = $how ?: self::LOCK_EXCLUSIVE;
        return $this;
    }

    function limit($count) {
        $this->limit = $count;
        return $this;
    }

    function offset($at) {
        $this->offset = $at;
        return $this;
    }

    function select_related() {
        $this->related = array_merge($this->related, func_get_args());
        return $this;
    }

    function values() {
        $this->values = func_get_args();
        $this->iterator = 'HashArrayIterator';
        return $this;
    }

    function values_flat() {
        $this->values = func_get_args();
        $this->iterator = 'FlatArrayIterator';
        return $this;
    }

    function all() {
        return $this->getIterator()->asArray();
    }

    function one() {
        $list = $this->limit(1)->all();
        if (count($list) == 0)
            throw new DoesNotExist();
        elseif (count($list) > 1)
            throw new ObjectNotUnique('One object was expected; however '
                .'multiple objects in the database matched the query. '
                .sprintf('In fact, there are %d matching objects.', count($list))
            );
        // TODO: Throw error if more than one result from database
        return $this[0];
    }

    function count() {
        $class = $this->compiler;
        $compiler = new $class();
        return $compiler->compileCount($this);
    }

    function exists() {
        return $this->count() > 0;
    }

    function delete() {
        $class = $this->compiler;
        $compiler = new $class();
        $ex = $compiler->compileBulkDelete($this);
        $ex->execute();
        return $ex->affected_rows();
    }

    function update(array $what) {
        $class = $this->compiler;
        $compiler = new $class;
        $ex = $compiler->compileBulkUpdate($this, $what);
        $ex->execute();
        return $ex->affected_rows();
    }

    function __clone() {
        unset($this->_iterator);
        unset($this->query);
    }

    // IteratorAggregate interface
    function getIterator() {
        $class = $this->iterator;
        if (!isset($this->_iterator))
            $this->_iterator = new $class($this);
        return $this->_iterator;
    }

    // ArrayAccess interface
    function offsetExists($offset) {
        return $this->getIterator()->offsetExists($offset);
    }
    function offsetGet($offset) {
        return $this->getIterator()->offsetGet($offset);
    }
    function offsetUnset($a) {
        throw new Exception(__('QuerySet is read-only'));
    }
    function offsetSet($a, $b) {
        throw new Exception(__('QuerySet is read-only'));
    }

    function __toString() {
        return (string) $this->getQuery();
    }

    function getQuery($options=array()) {
        if (isset($this->query))
            return $this->query;

        // Load defaults from model
        $model = $this->model;
        if (!$this->ordering && isset($model::$meta['ordering']))
            $this->ordering = $model::$meta['ordering'];

        $class = $this->compiler;
        $compiler = new $class($options);
        $this->query = $compiler->compileSelect($this);

        return $this->query;
    }
}

class DoesNotExist extends Exception {}
class ObjectNotUnique extends Exception {}

abstract class ResultSet implements Iterator, ArrayAccess {
    var $resource;
    var $position = 0;
    var $queryset;
    var $cache;

    function __construct($queryset=false) {
        $this->queryset = $queryset;
        if ($queryset) {
            $this->model = $queryset->model;
            $this->resource = $queryset->getQuery();
        }
    }

    abstract function fillTo($index);

    function asArray() {
        $this->fillTo(PHP_INT_MAX);
        return $this->cache;
    }

    // Iterator interface
    function rewind() {
        $this->position = 0;
    }
    function current() {
        $this->fillTo($this->position);
        return $this->cache[$this->position];
    }
    function key() {
        return $this->position;
    }
    function next() {
        $this->position++;
    }
    function valid() {
        $this->fillTo($this->position);
        return count($this->cache) > $this->position;
    }

    // ArrayAccess interface
    function offsetExists($offset) {
        $this->fillTo($offset);
        return $this->position >= $offset;
    }
    function offsetGet($offset) {
        $this->fillTo($offset);
        return $this->cache[$offset];
    }
    function offsetUnset($a) {
        throw new Exception(sprintf(__('%s is read-only'), get_class($this)));
    }
    function offsetSet($a, $b) {
        throw new Exception(sprintf(__('%s is read-only'), get_class($this)));
    }
}

class ModelInstanceManager extends ResultSet {
    var $model;
    var $map;

    static $objectCache = array();

    function __construct($queryset=false) {
        parent::__construct($queryset);
        if ($queryset) {
            $this->map = $this->resource->getMap();
        }
    }

    function cache($model) {
        $model::_inspect();
        $key = sprintf('%s.%s',
            $model::$meta->model, implode('.', $model->pk));
        self::$objectCache[$key] = $model;
    }

    /**
     * uncache
     *
     * Drop the cached reference to the model. If the model is deleted
     * database-side. Lookups for the same model should not be short
     * circuited to retrieve the cached reference.
     */
    static function uncache($model) {
        $key = sprintf('%s.%s',
            $model::$meta->model, implode('.', $model->pk));
        unset(self::$objectCache[$key]);
    }

    static function checkCache($modelClass, $fields) {
        $key = $modelClass::$meta->model;
        foreach ($modelClass::$meta['pk'] as $f)
            $key .= '.'.$fields[$f];
        return @self::$objectCache[$key];
    }

    function getOrBuild($modelClass, $fields) {
        // Check the cache for the model instance first
        if ($m = self::checkCache($modelClass, $fields)) {
            // TODO: If the model has deferred fields which are in $fields,
            // those can be resolved here
            return $m;
        }
        // Construct and cache the object
        $this->cache($m = new $modelClass($fields));
        $m->__deferred__ = $this->queryset->defer;
        $m->__onload();
        return $m;
    }

    /**
     * buildModel
     *
     * This method builds the model including related models from the record
     * received. For related recordsets, a $map should be setup inside this
     * object prior to using this method. The $map is assumed to have this
     * configuration:
     *
     * array(array(<modelClass>, <fieldCount>, <relativePath>, <alias>))
     *
     * Where $modelClass is the name of the foreign (with respect to the
     * root model ($this->model), $fieldCount is the number of fields in the
     * row for this model, $relativePath is the path that describes the
     * relationship between the root model and this model, 'user__account'
     * for instance, and <alias> is the alias for the model in the databse
     * query — the field names should all start with <alias>_
     */
    function buildModel($row) {
        // TODO: Traverse to foreign keys
        if ($this->map) {
            if ($this->model != $this->map[0][1])
                throw new OrmException('Internal select_related error');

            $offset = 0;
            foreach ($this->map as $info) {
                @list($count, $model_class, $path, $alias) = $info;
                $fields = array_slice($row, $offset, $count);
                if (!$path) {
                    // Build the root model
                    $model = $this->getOrBuild($this->model, $fields);
                    $model->__onload();
                }
                else {
                    foreach ($fields as $name=>$val) {
                        $fields[substr($name, strlen($alias)+1)] = $val;
                        unset($fields[$name]);
                    }
                    // Link the related model
                    $tail = array_pop($path);
                    $m = $model;
                    foreach ($path as $field) {
                        $m = $m->get($field);
                    }
                    $m->set($tail, $this->getOrBuild($model_class, $fields));
                }
                $offset += $count;
            }
        }
        else {
            $model = $this->getOrBuild($this->model, $row);
        }
        return $model;
    }

    function fillTo($index) {
        while ($this->resource && $index >= count($this->cache)) {
            if ($row = $this->resource->getArray()) {
                $this->cache[] = $this->buildModel($row);
            } else {
                $this->resource->close();
                $this->resource = null;
                break;
            }
        }
    }
}

class FlatArrayIterator extends ResultSet {
    function __construct($queryset) {
        $this->resource = $queryset->getQuery();
    }
    function fillTo($index) {
        while ($this->resource && $index >= count($this->cache)) {
            if ($row = $this->resource->getRow()) {
                $this->cache[] = $row;
            } else {
                $this->resource->close();
                $this->resource = null;
                break;
            }
        }
    }
}

class InstrumentedList extends ModelInstanceManager {
    var $key;
    var $id;
    var $model;

    function __construct($fkey, $queryset=false) {
        list($model, $this->key, $this->id) = $fkey;
        if (!$queryset)
            $queryset = $model::objects()->filter(array($this->key=>$this->id));
        parent::__construct($queryset);
        $this->model = $model;
        if (!$this->id)
            $this->resource = null;
    }

    function add($object, $at=false) {
        if (!$object || !$object instanceof $this->model)
            throw new Exception(__('Attempting to add invalid object to list'));

        $object->set($this->key, $this->id);
        $object->save();

        if ($at !== false)
            $this->cache[$at] = $object;
        else
            $this->cache[] = $object;
    }
    function remove($object) {
        $object->delete();
    }

    function reset() {
        $this->cache = array();
    }

    // QuerySet delegates
    function count() {
        return $this->queryset->count();
    }
    function exists() {
        return $this->queryset->exists();
    }
    function expunge() {
        if ($this->queryset->delete())
            $this->reset();
    }
    function update(array $what) {
        return $this->queryset->update($what);
    }

    // Fetch a new QuerySet
    function objects() {
        return clone $this->queryset;
    }

    function offsetUnset($a) {
        $this->fillTo($a);
        $this->cache[$a]->delete();
    }
    function offsetSet($a, $b) {
        $this->fillTo($a);
        $this->cache[$a]->delete();
        $this->add($b, $a);
    }
}

class SqlCompiler {
    var $options = array();
    var $params = array();
    var $joins = array();
    var $aliases = array();
    var $alias_num = 1;

    static $operators = array(
        'exact' => '%$1s = %$2s'
    );

    function __construct($options=false) {
        if ($options)
            $this->options = array_merge($this->options, $options);
    }

    /**
     * Handles breaking down a field or model search descriptor into the
     * model search path, field, and operator parts. When used in a queryset
     * filter, an expression such as
     *
     * user__email__hostname__contains => 'foobar'
     *
     * would be broken down to search from the root model (passed in,
     * perhaps a ticket) to the user and email models by inspecting the
     * model metadata 'joins' property. The 'constraint' value found there
     * will be used to build the JOIN sql clauses.
     *
     * The 'hostname' will be the field on 'email' model that should be
     * compared in the WHERE clause. The comparison should be made using a
     * 'contains' function, which in MySQL, might be implemented using
     * something like "<lhs> LIKE '%foobar%'"
     *
     * This function will rely heavily on the pushJoin() function which will
     * handle keeping track of joins made previously in the query and
     * therefore prevent multiple joins to the same table for the same
     * reason. (Self joins are still supported).
     *
     * Comparison functions supported by this function are defined for each
     * respective SqlCompiler subclass; however at least these functions
     * should be defined:
     *
     *      function    a__function => b
     *      ----------+------------------------------------------------
     *      exact     | a is exactly equal to b
     *      gt        | a is greater than b
     *      lte       | b is greater than a
     *      lt        | a is less than b
     *      gte       | b is less than a
     *      ----------+------------------------------------------------
     *      contains  | (string) b is contained within a
     *      statswith | (string) first len(b) chars of a are exactly b
     *      endswith  | (string) last len(b) chars of a are exactly b
     *      like      | (string) a matches pattern b
     *      ----------+------------------------------------------------
     *      in        | a is in the list or the nested queryset b
     *      ----------+------------------------------------------------
     *      isnull    | a is null (if b) else a is not null
     *
     * If no comparison function is declared in the field descriptor,
     * 'exact' is assumed.
     */
    function getField($field, $model, $options=array()) {
        $joins = array();

        // Break apart the field descriptor by __ (double-underbars). The
        // first part is assumed to be the root field in the given model.
        // The parts after each of the __ pieces are links to other tables.
        // The last item (after the last __) is allowed to be an operator
        // specifiction.
        $parts = explode('__', $field);
        $operator = static::$operators['exact'];
        if (!isset($options['table'])) {
            $field = array_pop($parts);
            if (array_key_exists($field, static::$operators)) {
                $operator = static::$operators[$field];
                $field = array_pop($parts);
            }
        }

        $path = array();
        $crumb = '';
        $alias = (isset($this->joins['']))
            ? $this->joins['']['alias']
            : $this->quote($model::$meta['table']);

        // Traverse through the parts and establish joins between the tables
        // if the field is joined to a foreign model
        if (count($parts) && isset($model::$meta['joins'][$parts[0]])) {
            // Call pushJoin for each segment in the join path. A new
            // JOIN fragment will need to be emitted and/or cached
            foreach ($parts as $p) {
                $path[] = $p;
                $tip = implode('__', $path);
                if (!($info = $model::$meta['joins'][$p])) {
                    throw new OrmException(sprintf(
                       'Model `%s` does not have a relation called `%s`',
                        $model, $p));
                }
                $alias = $this->pushJoin($crumb, $tip, $model, $info);
                // Roll to foreign model
                foreach ($info['constraint'] as $local => $foreign) {
                    list($model, $f) = explode('.', $foreign);
                    if (class_exists($model))
                        break;
                }
                $crumb = $tip;
            }
        }
        if (isset($options['table']) && $options['table'])
            $field = $alias;
        elseif ($alias)
            $field = $alias.'.'.$this->quote($field);
        else
            $field = $this->quote($field);
        if (isset($options['model']) && $options['model'])
            $operator = $model;
        return array($field, $operator);
    }

    /**
     * Uses the compiler-specific `compileJoin` function to compile the join
     * statement fragment, and caches the result in the local $joins list. A
     * new alias is acquired using the `nextAlias` function which will be
     * associated with the join. If the same path is requested again, the
     * algorithm is short-circuited and the originally-assigned table alias
     * is returned immediately.
     */
    function pushJoin($tip, $path, $model, $info) {
        // TODO: Build the join statement fragment and return the table
        // alias. The table alias will be useful where the join is used in
        // the WHERE and ORDER BY clauses

        // If the join already exists for the statement-being-compiled, just
        // return the alias being used.
        if (isset($this->joins[$path]))
            return $this->joins[$path]['alias'];

        // TODO: Support only using aliases if necessary. Use actual table
        // names for everything except oddities like self-joins

        $alias = $this->nextAlias();
        // Keep an association between the table alias and the model. This
        // will make model construction much easier when we have the data
        // and the table alias from the database.
        $this->aliases[$alias] = $model;

        // TODO: Stash joins and join constraints into local ->joins array.
        // This will be useful metadata in the executor to construct the
        // final models for fetching
        // TODO: Always use a table alias. This will further help with
        // coordination between the data returned from the database (where
        // table alias is available) and the corresponding data.
        $this->joins[$path] = array(
            'alias' => $alias,
            'sql'=> $this->compileJoin($tip, $model, $alias, $info),
        );
        return $alias;
    }

    function compileQ(Q $Q, $model) {
        $filter = array();