*
         * The table should be the name of the table to join to.
         *
         * The constraint may be either a string or an array with three elements. If it
         * is a string, it will be compiled into the query as-is, with no escaping. The
         * recommended way to supply the constraint is as an array with three elements:
         *
         * first_column, operator, second_column
         *
         * Example: array('user.id', '=', 'profile.user_id')
         *
         * will compile to
         *
         * ON `user`.`id` = `profile`.`user_id`
         *
         * The final (optional) argument specifies an alias for the joined table.
         */
        protected function _add_join_source($join_operator, $table, $constraint, $table_alias=null) {

            $join_operator = trim("{$join_operator} JOIN");

            $table = $this->_quote_identifier($table);

            // Add table alias if present
            if (!is_null($table_alias)) {
                $table_alias = $this->_quote_identifier($table_alias);
                $table .= " {$table_alias}";
            }

            // Build the constraint
            if (is_array($constraint)) {
                list($first_column, $operator, $second_column) = $constraint;
                $first_column = $this->_quote_identifier($first_column);
                $second_column = $this->_quote_identifier($second_column);
                $constraint = "{$first_column} {$operator} {$second_column}";
            }

            $this->_join_sources[] = "{$join_operator} {$table} ON {$constraint}";
            return $this;
        }

        /**
         * Add a RAW JOIN source to the query
         */
        public function raw_join($table, $constraint, $table_alias, $parameters = array()) {
            // Add table alias if present
            if (!is_null($table_alias)) {
                $table_alias = $this->_quote_identifier($table_alias);
                $table .= " {$table_alias}";
            }

            $this->_values = array_merge($this->_values, $parameters);

            // Build the constraint
            if (is_array($constraint)) {
                list($first_column, $operator, $second_column) = $constraint;
                $first_column = $this->_quote_identifier($first_column);
                $second_column = $this->_quote_identifier($second_column);
                $constraint = "{$first_column} {$operator} {$second_column}";
            }

            $this->_join_sources[] = "{$table} ON {$constraint}";
            return $this;
        }

        /**
         * Add a simple JOIN source to the query
         */
        public function join($table, $constraint, $table_alias=null) {
            return $this->_add_join_source("", $table, $constraint, $table_alias);
        }

        /**
         * Add an INNER JOIN souce to the query
         */
        public function inner_join($table, $constraint, $table_alias=null) {
            return $this->_add_join_source("INNER", $table, $constraint, $table_alias);
        }

        /**
         * Add a LEFT OUTER JOIN souce to the query
         */
        public function left_outer_join($table, $constraint, $table_alias=null) {
            return $this->_add_join_source("LEFT OUTER", $table, $constraint, $table_alias);
        }

        /**
         * Add an RIGHT OUTER JOIN souce to the query
         */
        public function right_outer_join($table, $constraint, $table_alias=null) {
            return $this->_add_join_source("RIGHT OUTER", $table, $constraint, $table_alias);
        }

        /**
         * Add an FULL OUTER JOIN souce to the query
         */
        public function full_outer_join($table, $constraint, $table_alias=null) {
            return $this->_add_join_source("FULL OUTER", $table, $constraint, $table_alias);
        }

        /**
         * Internal method to add a HAVING condition to the query
         */
        protected function _add_having($fragment, $values=array()) {
            return $this->_add_condition('having', $fragment, $values);
        }

        /**
         * Internal method to add a HAVING condition to the query
         */
        protected function _add_simple_having($column_name, $separator, $value) {
            return $this->_add_simple_condition('having', $column_name, $separator, $value);
        }

        /**
         * Internal method to add a HAVING clause with multiple values (like IN and NOT IN)
         */
        public function _add_having_placeholder($column_name, $separator, $values) {
            if (!is_array($column_name)) {
                $data = array($column_name => $values);
            } else {
                $data = $column_name;
            }
            $result = $this;
            foreach ($data as $key => $val) {
                $column = $result->_quote_identifier($key);
                $placeholders = $result->_create_placeholders($val);
                $result = $result->_add_having("{$column} {$separator} ({$placeholders})", $val);
            }
            return $result;
        }

        /**
         * Internal method to add a HAVING clause with no parameters(like IS NULL and IS NOT NULL)
         */
        public function _add_having_no_value($column_name, $operator) {
            $conditions = (is_array($column_name)) ? $column_name : array($column_name);
            $result = $this;
            foreach($conditions as $column) {
                $column = $this->_quote_identifier($column);
                $result = $result->_add_having("{$column} {$operator}");
            }
            return $result;
        }

        /**
         * Internal method to add a WHERE condition to the query
         */
        protected function _add_where($fragment, $values=array()) {
            return $this->_add_condition('where', $fragment, $values);
        }

        /**
         * Internal method to add a WHERE condition to the query
         */
        protected function _add_simple_where($column_name, $separator, $value) {
            return $this->_add_simple_condition('where', $column_name, $separator, $value);
        }

        /**
         * Add a WHERE clause with multiple values (like IN and NOT IN)
         */
        public function _add_where_placeholder($column_name, $separator, $values) {
            if (!is_array($column_name)) {
                $data = array($column_name => $values);
            } else {
                $data = $column_name;
            }
            $result = $this;
            foreach ($data as $key => $val) {
                $column = $result->_quote_identifier($key);
                $placeholders = $result->_create_placeholders($val);
                $result = $result->_add_where("{$column} {$separator} ({$placeholders})", $val);
            }
            return $result;
        }

        /**
         * Add a WHERE clause with no parameters(like IS NULL and IS NOT NULL)
         */
        public function _add_where_no_value($column_name, $operator) {
            $conditions = (is_array($column_name)) ? $column_name : array($column_name);
            $result = $this;
            foreach($conditions as $column) {
                $column = $this->_quote_identifier($column);
                $result = $result->_add_where("{$column} {$operator}");
            }
            return $result;
        }

        /**
         * Internal method to add a HAVING or WHERE condition to the query
         */
        protected function _add_condition($type, $fragment, $values=array()) {
            $conditions_class_property_name = "_{$type}_conditions";
            if (!is_array($values)) {
                $values = array($values);
            }
            array_push($this->$conditions_class_property_name, array(
                self::CONDITION_FRAGMENT => $fragment,
                self::CONDITION_VALUES => $values,
            ));
            return $this;
        }

       /**
         * Helper method to compile a simple COLUMN SEPARATOR VALUE
         * style HAVING or WHERE condition into a string and value ready to
         * be passed to the _add_condition method. Avoids duplication
         * of the call to _quote_identifier
         *
         * If column_name is an associative array, it will add a condition for each column
         */
        protected function _add_simple_condition($type, $column_name, $separator, $value) {
            $multiple = is_array($column_name) ? $column_name : array($column_name => $value);
            $result = $this;

            foreach($multiple as $key => $val) {
                // Add the table name in case of ambiguous columns
                if (count($result->_join_sources) > 0 && strpos($key, '.') === false) {
                    $table = $result->_table_name;
                    if (!is_null($result->_table_alias)) {
                        $table = $result->_table_alias;
                    }

                    $key = "{$table}.{$key}";
                }
                $key = $result->_quote_identifier($key);
                $result = $result->_add_condition($type, "{$key} {$separator} ?", $val);
            }
            return $result;
        }

        /**
         * Return a string containing the given number of question marks,
         * separated by commas. Eg "?, ?, ?"
         */
        protected function _create_placeholders($fields) {
            if(!empty($fields)) {
                $db_fields = array();
                foreach($fields as $key => $value) {
                    // Process expression fields directly into the query
                    if(array_key_exists($key, $this->_expr_fields)) {
                        $db_fields[] = $value;
                    } else {
                        $db_fields[] = '?';
                    }
                }
                return implode(', ', $db_fields);
            }
        }

        /**
         * Helper method that filters a column/value array returning only those
         * columns that belong to a compound primary key.
         *
         * If the key contains a column that does not exist in the given array,
         * a null value will be returned for it.
         */
        protected function _get_compound_id_column_values($value) {
            $filtered = array();
            foreach($this->_get_id_column_name() as $key) {
                $filtered[$key] = isset($value[$key]) ? $value[$key] : null;
            }
            return $filtered;
        }

       /**
         * Helper method that filters an array containing compound column/value
         * arrays.
         */
        protected function _get_compound_id_column_values_array($values) {
            $filtered = array();
            foreach($values as $value) {
                $filtered[] = $this->_get_compound_id_column_values($value);
            }
            return $filtered;
        }

        /**
         * Add a WHERE column = value clause to your query. Each time
         * this is called in the chain, an additional WHERE will be
         * added, and these will be ANDed together when the final query
         * is built.
         *
         * If you use an array in $column_name, a new clause will be
         * added for each element. In this case, $value is ignored.
         */
        public function where($column_name, $value=null) {
            return $this->where_equal($column_name, $value);
        }

        /**
         * More explicitly named version of for the where() method.
         * Can be used if preferred.
         */
        public function where_equal($column_name, $value=null) {
            return $this->_add_simple_where($column_name, '=', $value);
        }

        /**
         * Add a WHERE column != value clause to your query.
         */
        public function where_not_equal($column_name, $value=null) {
            return $this->_add_simple_where($column_name, '!=', $value);
        }

        /**
         * Special method to query the table by its primary key
         *
         * If primary key is compound, only the columns that
         * belong to they key will be used for the query
         */
        public function where_id_is($id) {
            return (is_array($this->_get_id_column_name())) ?
                $this->where($this->_get_compound_id_column_values($id), null) :
                $this->where($this->_get_id_column_name(), $id);
        }

        /**
         * Allows adding a WHERE clause that matches any of the conditions
         * specified in the array. Each element in the associative array will
         * be a different condition, where the key will be the column name.
         *
         * By default, an equal operator will be used against all columns, but
         * it can be overriden for any or every column using the second parameter.
         *
         * Each condition will be ORed together when added to the final query.
         */
        public function where_any_is($values, $operator='=') {
            $data = array();
            $query = array("((");
            $first = true;
            foreach ($values as $value) {
                if ($first) {
                    $first = false;
                } else {
                    $query[] = ") OR (";
                }
                $firstsub = true;
                foreach($value as $key => $item) {
                    $op = is_string($operator) ? $operator : (isset($operator[$key]) ? $operator[$key] : '=');
                    if ($firstsub) {
                        $firstsub = false;
                    } else {
                        $query[] = "AND";
                    }
                    $query[] = $this->_quote_identifier($key);
                    $data[] = $item;
                    $query[] = $op . " ?";
                }
            }
            $query[] = "))";
            return $this->where_raw(implode(' ', $query), $data);
        }

        /**
         * Similar to where_id_is() but allowing multiple primary keys.
         *
         * If primary key is compound, only the columns that
         * belong to they key will be used for the query
         */
        public function where_id_in($ids) {
            return (is_array($this->_get_id_column_name())) ?
                $this->where_any_is($this->_get_compound_id_column_values_array($ids)) :
                $this->where_in($this->_get_id_column_name(), $ids);
        }

        /**
         * Add a WHERE ... LIKE clause to your query.
         */
        public function where_like($column_name, $value=null) {
            return $this->_add_simple_where($column_name, 'LIKE', $value);
        }

        /**
         * Add where WHERE ... NOT LIKE clause to your query.
         */
        public function where_not_like($column_name, $value=null) {
            return $this->_add_simple_where($column_name, 'NOT LIKE', $value);
        }

        /**
         * Add a WHERE ... > clause to your query
         */
        public function where_gt($column_name, $value=null) {
            return $this->_add_simple_where($column_name, '>', $value);
        }

        /**
         * Add a WHERE ... < clause to your query
         */
        public function where_lt($column_name, $value=null) {
            return $this->_add_simple_where($column_name, '<', $value);
        }

        /**
         * Add a WHERE ... >= clause to your query
         */
        public function where_gte($column_name, $value=null) {
            return $this->_add_simple_where($column_name, '>=', $value);
        }

        /**
         * Add a WHERE ... <= clause to your query
         */
        public function where_lte($column_name, $value=null) {
            return $this->_add_simple_where($column_name, '<=', $value);
        }

        /**
         * Add a WHERE ... IN clause to your query
         */
        public function where_in($column_name, $values) {
            return $this->_add_where_placeholder($column_name, 'IN', $values);
        }

        /**
         * Add a WHERE ... NOT IN clause to your query
         */
        public function where_not_in($column_name, $values) {
            return $this->_add_where_placeholder($column_name, 'NOT IN', $values);
        }

        /**
         * Add a WHERE column IS NULL clause to your query
         */
        public function where_null($column_name) {
            return $this->_add_where_no_value($column_name, "IS NULL");
        }

        /**
         * Add a WHERE column IS NOT NULL clause to your query
         */
        public function where_not_null($column_name) {
            return $this->_add_where_no_value($column_name, "IS NOT NULL");
        }

        /**
         * Add a raw WHERE clause to the query. The clause should
         * contain question mark placeholders, which will be bound
         * to the parameters supplied in the second argument.
         */
        public function where_raw($clause, $parameters=array()) {
            return $this->_add_where($clause, $parameters);
        }

        /**
         * Add a LIMIT to the query
         */
        public function limit($limit) {
            $this->_limit = $limit;
            return $this;
        }

        /**
         * Add an OFFSET to the query
         */
        public function offset($offset) {
            $this->_offset = $offset;
            return $this;
        }

        /**
         * Add an ORDER BY clause to the query
         */
        protected function _add_order_by($column_name, $ordering) {
            $column_name = $this->_quote_identifier($column_name);
            $this->_order_by[] = "{$column_name} {$ordering}";
            return $this;
        }

        /**
         * Add an ORDER BY column DESC clause
         */
        public function order_by_desc($column_name) {
            return $this->_add_order_by($column_name, 'DESC');
        }

        /**
         * Add an ORDER BY column ASC clause
         */
        public function order_by_asc($column_name) {
            return $this->_add_order_by($column_name, 'ASC');
        }

        /**
         * Add an unquoted expression as an ORDER BY clause
         */
        public function order_by_expr($clause) {
            $this->_order_by[] = $clause;
            return $this;
        }

        /**
         * Add a column to the list of columns to GROUP BY
         */
        public function group_by($column_name) {
            $column_name = $this->_quote_identifier($column_name);
            $this->_group_by[] = $column_name;
            return $this;
        }

        /**
         * Add an unquoted expression to the list of columns to GROUP BY
         */
        public function group_by_expr($expr) {
            $this->_group_by[] = $expr;
            return $this;
        }

        /**
         * Add a HAVING column = value clause to your query. Each time
         * this is called in the chain, an additional HAVING will be
         * added, and these will be ANDed together when the final query
         * is built.
         *
         * If you use an array in $column_name, a new clause will be
         * added for each element. In this case, $value is ignored.
         */
        public function having($column_name, $value=null) {
            return $this->having_equal($column_name, $value);
        }

        /**
         * More explicitly named version of for the having() method.
         * Can be used if preferred.
         */
        public function having_equal($column_name, $value=null) {
            return $this->_add_simple_having($column_name, '=', $value);
        }

        /**
         * Add a HAVING column != value clause to your query.
         */
        public function having_not_equal($column_name, $value=null) {
            return $this->_add_simple_having($column_name, '!=', $value);
        }

        /**
         * Special method to query the table by its primary key.
         *
         * If primary key is compound, only the columns that
         * belong to they key will be used for the query
         */
        public function having_id_is($id) {
            return (is_array($this->_get_id_column_name())) ?
                $this->having($this->_get_compound_id_column_values($id), null) :
                $this->having($this->_get_id_column_name(), $id);
        }

        /**
         * Add a HAVING ... LIKE clause to your query.
         */
        public function having_like($column_name, $value=null) {
            return $this->_add_simple_having($column_name, 'LIKE', $value);
        }

        /**
         * Add where HAVING ... NOT LIKE clause to your query.
         */
        public function having_not_like($column_name, $value=null) {
            return $this->_add_simple_having($column_name, 'NOT LIKE', $value);
        }

        /**
         * Add a HAVING ... > clause to your query
         */
        public function having_gt($column_name, $value=null) {
            return $this->_add_simple_having($column_name, '>', $value);
        }

        /**
         * Add a HAVING ... < clause to your query
         */
        public function having_lt($column_name, $value=null) {
            return $this->_add_simple_having($column_name, '<', $value);
        }

        /**
         * Add a HAVING ... >= clause to your query
         */
        public function having_gte($column_name, $value=null) {
            return $this->_add_simple_having($column_name, '>=', $value);
        }

        /**
         * Add a HAVING ... <= clause to your query
         */
        public function having_lte($column_name, $value=null) {
            return $this->_add_simple_having($column_name, '<=', $value);
        }

        /**
         * Add a HAVING ... IN clause to your query
         */
        public function having_in($column_name, $values=null) {
            return $this->_add_having_placeholder($column_name, 'IN', $values);
        }

        /**
         * Add a HAVING ... NOT IN clause to your query
         */
        public function having_not_in($column_name, $values=null) {
            return $this->_add_having_placeholder($column_name, 'NOT IN', $values);
        }

        /**
         * Add a HAVING column IS NULL clause to your query
         */
        public function having_null($column_name) {
            return $this->_add_having_no_value($column_name, 'IS NULL');
        }

        /**
         * Add a HAVING column IS NOT NULL clause to your query
         */
        public function having_not_null($column_name) {
            return $this->_add_having_no_value($column_name, 'IS NOT NULL');
        }

        /**
         * Add a raw HAVING clause to the query. The clause should
         * contain question mark placeholders, which will be bound
         * to the parameters supplied in the second argument.
         */
        public function having_raw($clause, $parameters=array()) {
            return $this->_add_having($clause, $parameters);
        }

        /**
         * Build a SELECT statement based on the clauses that have
         * been passed to this instance by chaining method calls.
         */
        protected function _build_select() {
            // If the query is raw, just set the $this->_values to be
            // the raw query parameters and return the raw query
            if ($this->_is_raw_query) {
                $this->_values = $this->_raw_parameters;
                return $this->_raw_query;
            }

            // Build and return the full SELECT statement by concatenating
            // the results of calling each separate builder method.
            return $this->_join_if_not_empty(" ", array(
                $this->_build_select_start(),
                $this->_build_join(),
                $this->_build_where(),
                $this->_build_group_by(),
                $this->_build_having(),
                $this->_build_order_by(),
                $this->_build_limit(),
                $this->_build_offset(),
            ));
        }

        /**
         * Build the start of the SELECT statement
         */
        protected function _build_select_start() {
            $fragment = 'SELECT ';
            $result_columns = implode(', ', $this->_result_columns);

            if (!is_null($this->_limit) &&
                self::$_config[$this->_connection_name]['limit_clause_style'] === ORM::LIMIT_STYLE_TOP_N) {
                $fragment .= "TOP {$this->_limit} ";
            }

            if ($this->_distinct) {
                $result_columns = 'DISTINCT ' . $result_columns;
            }

            $fragment .= "{$result_columns} FROM " . $this->_quote_identifier($this->_table_name);

            if (!is_null($this->_table_alias)) {
                $fragment .= " " . $this->_quote_identifier($this->_table_alias);
            }
            return $fragment;
        }

        /**
         * Build the JOIN sources
         */
        protected function _build_join() {
            if (count($this->_join_sources) === 0) {
                return '';
            }

            return implode(' ', $this->_join_sources);
        }

        /**
         * Build the WHERE clause(s)
         */
        protected function _build_where() {
            return $this->_build_conditions('where');
        }

        /**
         * Build the HAVING clause(s)
         */
        protected function _build_having() {
            return $this->_build_conditions('having');
        }

        /**
         * Build GROUP BY
         */
        protected function _build_group_by() {
            if (count($this->_group_by) === 0) {
                return '';
            }
            return "GROUP BY " . implode(', ', $this->_group_by);
        }

        /**
         * Build a WHERE or HAVING clause
         * @param string $type
         * @return string
         */
        protected function _build_conditions($type) {
            $conditions_class_property_name = "_{$type}_conditions";
            // If there are no clauses, return empty string
            if (count($this->$conditions_class_property_name) === 0) {
                return '';
            }

            $conditions = array();
            foreach ($this->$conditions_class_property_name as $condition) {
                $conditions[] = $condition[self::CONDITION_FRAGMENT];
                $this->_values = array_merge($this->_values, $condition[self::CONDITION_VALUES]);
            }

            return strtoupper($type) . " " . implode(' AND ', $conditions);
        }

        /**
         * Build ORDER BY
         */
        protected function _build_order_by() {
            if (count($this->_order_by) === 0) {
                return '';
            }
            return "ORDER BY " . implode(', ', $this->_order_by);
        }

        /**
         * Build LIMIT
         */
        protected function _build_limit() {
            $fragment = '';
            if (!is_null($this->_limit) &&
                self::$_config[$this->_connection_name]['limit_clause_style'] == ORM::LIMIT_STYLE_LIMIT) {
                if (self::get_db($this->_connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME) == 'firebird') {
                    $fragment = 'ROWS';
                } else {
                    $fragment = 'LIMIT';
                }
                $fragment .= " {$this->_limit}";
            }
            return $fragment;
        }

        /**
         * Build OFFSET
         */
        protected function _build_offset() {
            if (!is_null($this->_offset)) {
                $clause = 'OFFSET';
                if (self::get_db($this->_connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME) == 'firebird') {
                    $clause = 'TO';
                }
                return "$clause " . $this->_offset;
            }
            return '';
        }

        /**
         * Wrapper around PHP's join function which
         * only adds the pieces if they are not empty.
         */
        protected function _join_if_not_empty($glue, $pieces) {
            $filtered_pieces = array();
            foreach ($pieces as $piece) {
                if (is_string($piece)) {
                    $piece = trim($piece);
                }
                if (!empty($piece)) {
                    $filtered_pieces[] = $piece;
                }
            }
            return implode($glue, $filtered_pieces);
        }

        /**
         * Quote a string that is used as an identifier
         * (table names, column names etc). This method can
         * also deal with dot-separated identifiers eg table.column
         */
        protected function _quote_one_identifier($identifier) {
            $parts = explode('.', $identifier);
            $parts = array_map(array($this, '_quote_identifier_part'), $parts);
            return implode('.', $parts);
        }

        /**
         * Quote a string that is used as an identifier
         * (table names, column names etc) or an array containing
         * multiple identifiers. This method can also deal with
         * dot-separated identifiers eg table.column
         */
        protected function _quote_identifier($identifier) {
            if (is_array($identifier)) {
                $result = array_map(array($this, '_quote_one_identifier'), $identifier);
                return implode(', ', $result);
            } else {
                return $this->_quote_one_identifier($identifier);
            }
        }

        /**
         * This method performs the actual quoting of a single
         * part of an identifier, using the identifier quote
         * character specified in the config (or autodetected).
         */
        protected function _quote_identifier_part($part) {
            if ($part === '*') {
                return $part;
            }

            $quote_character = self::$_config[$this->_connection_name]['identifier_quote_character'];
            // double up any identifier quotes to escape them
            return $quote_character .
                   str_replace($quote_character,
                               $quote_character . $quote_character,
                               $part
                   ) . $quote_character;
        }

        /**
         * Create a cache key for the given query and parameters.
         */
        protected static function _create_cache_key($query, $parameters, $table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
            if(isset(self::$_config[$connection_name]['create_cache_key']) and is_callable(self::$_config[$connection_name]['create_cache_key'])){
                return call_user_func_array(self::$_config[$connection_name]['create_cache_key'], array($query, $parameters, $table_name, $connection_name));
            }
            $parameter_string = implode(',', $parameters);
            $key = $query . ':' . $parameter_string;
            return sha1($key);
        }

        /**
         * Check the query cache for the given cache key. If a value
         * is cached for the key, return the value. Otherwise, return false.
         */
        protected static function _check_query_cache($cache_key, $table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
            if(isset(self::$_config[$connection_name]['check_query_cache']) and is_callable(self::$_config[$connection_name]['check_query_cache'])){
                return call_user_func_array(self::$_config[$connection_name]['check_query_cache'], array($cache_key, $table_name, $connection_name));
            } elseif (isset(self::$_query_cache[$connection_name][$cache_key])) {
                return self::$_query_cache[$connection_name][$cache_key];
            }
            return false;
        }

        /**
         * Clear the query cache
         */
        public static function clear_cache($table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
            self::$_query_cache = array();
            if(isset(self::$_config[$connection_name]['clear_cache']) and is_callable(self::$_config[$connection_name]['clear_cache'])){
                return call_user_func_array(self::$_config[$connection_name]['clear_cache'], array($table_name, $connection_name));
            }
        }

        /**
         * Add the given value to the query cache.
         */
        protected static function _cache_query_result($cache_key, $value, $table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
            if(isset(self::$_config[$connection_name]['cache_query_result']) and is_callable(self::$_config[$connection_name]['cache_query_result'])){
                return call_user_func_array(self::$_config[$connection_name]['cache_query_result'], array($cache_key, $value, $table_name, $connection_name));
            } elseif (!isset(self::$_query_cache[$connection_name])) {
                self::$_query_cache[$connection_name] = array();
            }
            self::$_query_cache[$connection_name][$cache_key] = $value;
        }

        /**
         * Execute the SELECT query that has been built up by chaining methods
         * on this class. Return an array of rows as associative arrays.
         */
        protected function _run() {
            $query = $this->_build_select();
            $caching_enabled = self::$_config[$this->_connection_name]['caching'];

            if ($caching_enabled) {
                $cache_key = self::_create_cache_key($query, $this->_values, $this->_table_name, $this->_connection_name);
                $cached_result = self::_check_query_cache($cache_key, $this->_table_name, $this->_connection_name);

                if ($cached_result !== false) {
                    $this->_reset_idiorm_state();
                    return $cached_result;
                }
            }

            self::_execute($query, $this->_values, $this->_connection_name);
            $statement = self::get_last_statement();

            $rows = array();
            while ($row = $statement->fetch(PDO::FETCH_ASSOC)) {
                $rows[] = $row;
            }

            if ($caching_enabled) {
                self::_cache_query_result($cache_key, $rows, $this->_table_name, $this->_connection_name);
            }

            $this->_reset_idiorm_state();
            return $rows;
        }

        /**
         * Reset the Idiorm instance state
         */
        private function _reset_idiorm_state() {
            $this->_values = array();
            $this->_result_columns = array('*');
            $this->_using_default_result_columns = true;
        }

        /**
         * Return the raw data wrapped by this ORM
         * instance as an associative array. Column
         * names may optionally be supplied as arguments,
         * if so, only those keys will be returned.
         */
        public function as_array() {
            if (func_num_args() === 0) {
                return $this->_data;
            }
            $args = func_get_args();
            return array_intersect_key($this->_data, array_flip($args));
        }

        /**
         * Return the value of a property of this object (database row)
         * or null if not present.
         *
         * If a column-names array is passed, it will return a associative array
         * with the value of each column or null if it is not present.
         */
        public function get($key) {
            if (is_array($key)) {
                $result = array();
                foreach($key as $column) {
                    $result[$column] = isset($this->_data[$column]) ? $this->_data[$column] : null;
                }
                return $result;
            } else {
                return isset($this->_data[$key]) ? $this->_data[$key] : null;
            }
        }

        /**
         * Return the name of the column in the database table which contains
         * the primary key ID of the row.
         */
        protected function _get_id_column_name() {
            if (!is_null($this->_instance_id_column)) {
                return $this->_instance_id_column;
            }
            if (isset(self::$_config[$this->_connection_name]['id_column_overrides'][$this->_table_name])) {
                return self::$_config[$this->_connection_name]['id_column_overrides'][$this->_table_name];
            }
            return self::$_config[$this->_connection_name]['id_column'];
        }

        /**
         * Get the primary key ID of this object.
         */
        public function id($disallow_null = false) {
            $id = $this->get($this->_get_id_column_name());

            if ($disallow_null) {
                if (is_array($id)) {
                    foreach ($id as $id_part) {
                        if ($id_part === null) {
                            throw new Exception('Primary key ID contains null value(s)');
                        }
                    }
                } else if ($id === null) {
                    throw new Exception('Primary key ID missing from row or is null');
                }
            }

            return $id;
        }

        /**
         * Set a property to a particular value on this object.
         * To set multiple properties at once, pass an associative array
         * as the first parameter and leave out the second parameter.
         * Flags the properties as 'dirty' so they will be saved to the
         * database when save() is called.
         */
        public function set($key, $value = null) {
            return $this->_set_orm_property($key, $value);
        }

        /**
         * Set a property to a particular value on this object.
         * To set multiple properties at once, pass an associative array
         * as the first parameter and leave out the second parameter.
         * Flags the properties as 'dirty' so they will be saved to the
         * database when save() is called.
         * @param string|array $key
         * @param string|null $value
         */
        public function set_expr($key, $value = null) {
            return $this->_set_orm_property($key, $value, true);
        }

        /**
         * Set a property on the ORM object.
         * @param string|array $key
         * @param string|null $value
         * @param bool $raw Whether this value should be treated as raw or not
         */
        protected function _set_orm_property($key, $value = null, $expr = false) {
            if (!is_array($key)) {
                $key = array($key => $value);
            }
            foreach ($key as $field => $value) {
                $this->_data[$field] = $value;
                $this->_dirty_fields[$field] = $value;
                if (false === $expr and isset($this->_expr_fields[$field])) {
                    unset($this->_expr_fields[$field]);
                } else if (true === $expr) {
                    $this->_expr_fields[$field] = true;
                }
            }
            return $this;
        }

        /**
         * Check whether the given field has been changed since this
         * object was saved.
         */
        public function is_dirty($key) {
            return array_key_exists($key, $this->_dirty_fields);
        }

        /**
         * Check whether the model was the result of a call to create() or not
         * @return bool
         */
        public function is_new() {
            return $this->_is_new;
        }

        /**
         * Save any fields which have been modified on this object
         * to the database.
         */
        public function save() {
            $query = array();

            // remove any expression fields as they are already baked into the query
            $values = array_values(array_diff_key($this->_dirty_fields, $this->_expr_fields));

            if (!$this->_is_new) { // UPDATE
                // If there are no dirty values, do nothing
                if (empty($values) && empty($this->_expr_fields)) {
                    return true;
                }
                $query = $this->_build_update();
                $id = $this->id(true);
                if (is_array($id)) {
                    $values = array_merge($values, array_values($id));
                } else {
                    $values[] = $id;
                }
            } else { // INSERT
                $query = $this->_build_insert();
            }

            $success = self::_execute($query, $values, $this->_connection_name);
            $caching_auto_clear_enabled = self::$_config[$this->_connection_name]['caching_auto_clear'];
            if($caching_auto_clear_enabled){
                self::clear_cache($this->_table_name, $this->_connection_name);
            }
            // If we've just inserted a new record, set the ID of this object
            if ($this->_is_new) {
                $this->_is_new = false;
                if ($this->count_null_id_columns() != 0) {
                    $db = self::get_db($this->_connection_name);
                    if($db->getAttribute(PDO::ATTR_DRIVER_NAME) == 'pgsql') {
                        // it may return several columns if a compound primary
                        // key is used
                        $row = self::get_last_statement()->fetch(PDO::FETCH_ASSOC);
                        foreach($row as $key => $value) {
                            $this->_data[$key] = $value;
                        }
                    } else {
                        $column = $this->_get_id_column_name();
                        // if the primary key is compound, assign the last inserted id
                        // to the first column
                        if (is_array($column)) {
                            $column = reset($column);
                        }
                        $this->_data[$column] = $db->lastInsertId();
                    }
                }
            }

            $this->_dirty_fields = $this->_expr_fields = array();
            return $success;
        }

        /**
         * Add a WHERE clause for every column that belongs to the primary key
         */
        public function _add_id_column_conditions(&$query) {
            $query[] = "WHERE";
            $keys = is_array($this->_get_id_column_name()) ? $this->_get_id_column_name() : array( $this->_get_id_column_name() );
            $first = true;
            foreach($keys as $key) {
                if ($first) {
                    $first = false;
                }
                else {
                    $query[] = "AND";
                }
                $query[] = $this->_quote_identifier($key);
                $query[] = "= ?";
            }
        }

        /**
         * Build an UPDATE query
         */
        protected function _build_update() {
            $query = array();
            $query[] = "UPDATE {$this->_quote_identifier($this->_table_name)} SET";

            $field_list = array();
            foreach ($this->_dirty_fields as $key => $value) {
                if(!array_key_exists($key, $this->_expr_fields)) {
                    $value = '?';
                }
                $field_list[] = "{$this->_quote_identifier($key)} = $value";
            }
            $query[] = implode(', ', $field_list);
            $this->_add_id_column_conditions($query);
            return implode(' ', $query);
        }

        /**
         * Build an INSERT query
         */
        protected function _build_insert() {
            $query[] = "INSERT INTO";
            $query[] = $this->_quote_identifier($this->_table_name);
            $field_list = array_map(array($this, '_quote_identifier'), array_keys($this->_dirty_fields));
            $query[] = "(" . implode(', ', $field_list) . ")";
            $query[] = "VALUES";

            $placeholders = $this->_create_placeholders($this->_dirty_fields);
            $query[] = "({$placeholders})";

            if (self::get_db($this->_connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME) == 'pgsql') {
                $query[] = 'RETURNING ' . $this->_quote_identifier($this->_get_id_column_name());
            }

            return implode(' ', $query);
        }

        /**
         * Delete this record from the database
         */
        public function delete() {
            $query = array(
                "DELETE FROM",
                $this->_quote_identifier($this->_table_name)
            );
            $this->_add_id_column_conditions($query);
            return self::_execute(implode(' ', $query), is_array($this->id(true)) ? array_values($this->id(true)) : array($this->id(true)), $this->_connection_name);
        }

        /**
         * Delete many records from the database
         */
        public function delete_many() {
            // Build and return the full DELETE statement by concatenating
            // the results of calling each separate builder method.
            $query = $this->_join_if_not_empty(" ", array(
                "DELETE FROM",
                $this->_quote_identifier($this->_table_name),
                $this->_build_where(),
            ));

            return self::_execute($query, $this->_values, $this->_connection_name);
        }

        // --------------------- //
        // ---  ArrayAccess  --- //
        // --------------------- //

        public function offsetExists($key): bool {
            return array_key_exists($key, $this->_data);
        }

        #[\ReturnTypeWillChange] // Need to use annotation since mixed was added in 8.0
        public function offsetGet($key) {
            return $this->get($key);
        }

        public function offsetSet($key, $value): void {
            if(is_null($key)) {
                throw new InvalidArgumentException('You must specify a key/array index.');
            }
            $this->set($key, $value);
        }

        public function offsetUnset($key): void {
            unset($this->_data[$key]);
            unset($this->_dirty_fields[$key]);
        }

        // --------------------- //
        // --- MAGIC METHODS --- //
        // --------------------- //
        public function __get($key) {
            return $this->offsetGet($key);
        }

        public function __set($key, $value) {
            $this->offsetSet($key, $value);
        }

        public function __unset($key) {
            $this->offsetUnset($key);
        }


        public function __isset($key) {
            return $this->offsetExists($key);
        }

        /**
         * Magic method to capture calls to undefined class methods.
         * In this case we are attempting to convert camel case formatted
         * methods into underscore formatted methods.
         *
         * This allows us to call ORM methods using camel case and remain
         * backwards compatible.
         *
         * @param  string   $name
         * @param  array    $arguments
         * @return ORM
         */
        public function __call($name, $arguments)
        {
            $method = strtolower(preg_replace('/([a-z])([A-Z])/', '$1_$2', $name));

            if (method_exists($this, $method)) {
                return call_user_func_array(array($this, $method), $arguments);
            } else {
                throw new IdiormMethodMissingException("Method $name() does not exist in class " . get_class($this));
            }
        }

        /**
         * Magic method to capture calls to undefined static class methods.
         * In this case we are attempting to convert camel case formatted
         * methods into underscore formatted methods.
         *
         * This allows us to call ORM methods using camel case and remain
         * backwards compatible.
         *
         * @param  string   $name
         * @param  array    $arguments
         * @return ORM
         */
        public static function __callStatic($name, $arguments)
        {
            $method = strtolower(preg_replace('/([a-z])([A-Z])/', '$1_$2', $name));

            return call_user_func_array(array('MailPoetVendor\Idiorm\ORM', $method), $arguments);
        }
    }

    /**
     * A class to handle str_replace operations that involve quoted strings
     * @example IdiormString::str_replace_outside_quotes('?', '%s', 'columnA = "Hello?" AND columnB = ?');
     * @example IdiormString::value('columnA = "Hello?" AND columnB = ?')->replace_outside_quotes('?', '%s');
     * @author Jeff Roberson <ridgerunner@fluxbb.org>
     * @author Simon Holywell <treffynnon@php.net>
     * @link http://stackoverflow.com/a/13370709/461813 StackOverflow answer
     */
    class IdiormString {
        protected $subject;
        protected $search;
        protected $replace;

        /**
         * Get an easy to use instance of the class
         * @param string $subject
         * @return \self
         */
        public static function value($subject) {
            return new self($subject);
        }

        /**
         * Shortcut method: Replace all occurrences of the search string with the replacement
         * string where they appear outside quotes.
         * @param string $search
         * @param string $replace
         * @param string $subject
         * @return string
         */
        public static function str_replace_outside_quotes($search, $replace, $subject) {
            return self::value($subject)->replace_outside_quotes($search, $replace);
        }

        /**
         * Set the base string object
         * @param string $subject
         */
        public function __construct($subject) {
            $this->subject = (string) $subject;
        }

        /**
         * Replace all occurrences of the search string with the replacement
         * string where they appear outside quotes
         * @param string $search
         * @param string $replace
         * @return string
         */
        public function replace_outside_quotes($search, $replace) {
            $this->search = $search;
            $this->replace = $replace;
            return $this->_str_replace_outside_quotes();
        }

        /**
         * Validate an input string and perform a replace on all ocurrences
         * of $this->search with $this->replace
         * @author Jeff Roberson <ridgerunner@fluxbb.org>
         * @link http://stackoverflow.com/a/13370709/461813 StackOverflow answer
         * @return string
         */
        protected function _str_replace_outside_quotes(){
            $re_valid = '/
                # Validate string having embedded quoted substrings.
                ^                           # Anchor to start of string.
                (?:                         # Zero or more string chunks.
                  "[^"\\\\]*(?:\\\\.[^"\\\\]*)*"  # Either a double quoted chunk,
                | \'[^\'\\\\]*(?:\\\\.[^\'\\\\]*)*\'  # or a single quoted chunk,
                | [^\'"\\\\]+               # or an unquoted chunk (no escapes).
                )*                          # Zero or more string chunks.
                \z                          # Anchor to end of string.
                /sx';
            if (!preg_match($re_valid, $this->subject)) {
                throw new IdiormStringException("Subject string is not valid in the replace_outside_quotes context.");
            }
            $re_parse = '/
                # Match one chunk of a valid string having embedded quoted substrings.
                  (                         # Either $1: Quoted chunk.
                    "[^"\\\\]*(?:\\\\.[^"\\\\]*)*"  # Either a double quoted chunk,
                  | \'[^\'\\\\]*(?:\\\\.[^\'\\\\]*)*\'  # or a single quoted chunk.
                  )                         # End $1: Quoted chunk.
                | ([^\'"\\\\]+)             # or $2: an unquoted chunk (no escapes).
                /sx';
            return preg_replace_callback($re_parse, array($this, '_str_replace_outside_quotes_cb'), $this->subject);
        }

        /**
         * Process each matching chunk from preg_replace_callback replacing
         * each occurrence of $this->search with $this->replace
         * @author Jeff Roberson <ridgerunner@fluxbb.org>
         * @link http://stackoverflow.com/a/13370709/461813 StackOverflow answer
         * @param array $matches
         * @return string
         */
        protected function _str_replace_outside_quotes_cb($matches) {
            // Return quoted string chunks (in group $1) unaltered.
            if ($matches[1]) return $matches[1];
            // Process only unquoted chunks (in group $2).
            return preg_replace('/'. preg_quote($this->search, '/') .'/',
                $this->replace, $matches[2]);
        }
    }

    /**
     * A result set class for working with collections of model instances
     * @author Simon Holywell <treffynnon@php.net>
     * @method null setResults(array $results)
     * @method array getResults()
     */
    class IdiormResultSet implements Countable, IteratorAggregate, ArrayAccess {
        /**
         * The current result set as an array
         * @var array
         */
        protected $_results = array();

        /**
         * Optionally set the contents of the result set by passing in array
         * @param array $results
         */
        public function __construct(array $results = array()) {
            $this->set_results($results);
        }

        /**
         * Set the contents of the result set by passing in array
         * @param array $results
         */
        public function set_results(array $results) {
            $this->_results = $results;
        }

        /**
         * Get the current result set as an array
         * @return array
         */
        public function get_results() {
            return $this->_results;
        }

        /**
         * Get the current result set as an array
         * @return array
         */
        public function as_array() {
            return $this->get_results();
        }

        /**
         * Get the number of records in the result set
         * @return int
         */
        public function count(): int {
            return count($this->_results);
        }

        /**
         * Get an iterator for this object. In this case it supports foreaching
         * over the result set.
         * @return \ArrayIterator
         */
        public function getIterator(): \Traversable {
            return new ArrayIterator($this->_results);
        }

        /**
         * ArrayAccess
         * @param int|string $offset
         * @return bool
         */
        public function offsetExists($offset): bool {
            return isset($this->_results[$offset]);
        }

        /**
         * ArrayAccess
         * @param int|string $offset
         * @return mixed
         */
        #[\ReturnTypeWillChange] // Can't use mixed return typehint since it was added in 8.0
        public function offsetGet($offset) {
            return $this->_results[$offset];
        }

        /**
         * ArrayAccess
         * @param int|string $offset
         * @param mixed $value
         */
        public function offsetSet($offset, $value): void {
            $this->_results[$offset] = $value;
        }

        /**
         * ArrayAccess
         * @param int|string $offset
         */
        public function offsetUnset($offset): void {
            unset($this->_results[$offset]);
        }

        /**
         * Serializable
         * @return string
         */
        public function serialize() {
            return serialize($this->_results);
        }

        public function __serialize() {
          return $this->serialize();
        }

        /**
         * Serializable
         * @param string $serialized
         * @return array
         */
        public function unserialize($serialized) {
            return unserialize($serialized);
        }

        public function __unserialize($serialized) {
          return $this->unserialize($serialized);
        }

        /**
         * Call a method on all models in a result set. This allows for method
         * chaining such as setting a property on all models in a result set or
         * any other batch operation across models.
         * @example ORM::for_table('Widget')->find_many()->set('field', 'value')->save();
         * @param string $method
         * @param array $params
         * @return IdiormResultSet
         */
        public function __call($method, $params = array()) {
            foreach($this->_results as $model) {
                if (method_exists($model, $method)) {
                    call_user_func_array(array($model, $method), $params);
                } else {
                    throw new IdiormMethodMissingException("Method $method() does not exist in class " . get_class($this));
                }
            }
            return $this;
        }
    }

    /**
     * A placeholder for exceptions eminating from the IdiormString class
     */
    class IdiormStringException extends Exception {}

    class IdiormMethodMissingException extends Exception {}