interface ConditionInterface

interface ConditionInterface {
    
    /**
     * Gets the current conjunction.
     *
     * @return string
     *   Can be AND or OR.
     */
    public function getConjunction();
    
    /**
     * Implements \Countable::count().
     *
     * Returns the size of this conditional. The size of the conditional is the
     * size of its conditional array.
     */
    public function count();
    
    /**
     * Adds a condition.
     *
     * @param string|\Drupal\Core\Entity\Query\ConditionInterface $field
     *   The field.
     * @param mixed $value
     *   (optional) The value.
     * @param string $operator
     *   (optional) The operator.
     * @param string $langcode
     *   (optional) For which language the entity should be prepared, defaults to
     *   the current content language.
     *
     * @return $this
     *
     * @see \Drupal\Core\Entity\Query\QueryInterface::condition()
     */
    public function condition($field, $value = NULL, $operator = NULL, $langcode = NULL);
    
    /**
     * Queries for the existence of a field.
     *
     * @param string $field
     *   The field to query for existence.
     * @param string $langcode
     *   (optional) For which language the entity should be prepared, defaults to
     *   the current content language.
     *
     * @return $this
     *
     * @see \Drupal\Core\Entity\Query\QueryInterface::exists()
     */
    public function exists($field, $langcode = NULL);
    
    /**
     * Queries for the nonexistence of a field.
     *
     * @param string $field
     *   The field to query for nonexistence.
     * @param string $langcode
     *   (optional) For which language the entity should be prepared, defaults to
     *   the current content language.
     *
     * @return $this
     *
     * @see \Drupal\Core\Entity\Query\QueryInterface::notExists()
     */
    public function notExists($field, $langcode = NULL);
    
    /**
     * Gets a complete list of all conditions in this conditional clause.
     *
     * This method returns by reference. That allows alter hooks to access the
     * data structure directly and manipulate it before it gets compiled.
     *
     * @return array
     */
    public function &conditions();
    
    /**
     * Compiles this conditional clause.
     *
     * @param $query
     *   The query object this conditional clause belongs to.
     */
    public function compile($query);

}