interface ConditionInterface

1. 8.x drupal/core/lib/Drupal/Core/Condition/ConditionInterface.php \Drupal\Core\Condition\ConditionInterface
2. 8.x drupal/core/lib/Drupal/Core/Database/Query/ConditionInterface.php \Drupal\Core\Database\Query\ConditionInterface
3. 8.x drupal/core/lib/Drupal/Core/Entity/Query/ConditionInterface.php \Drupal\Core\Entity\Query\ConditionInterface

Condition.php in drupal/core/lib/Drupal/Core/Config/Entity/Query/Condition.php

Contains \Drupal\Core\Config\Entity\Query\Condition.

Condition.php in drupal/core/modules/field_sql_storage/lib/Drupal/field_sql_storage/Entity/Condition.php

Definition of Drupal\field_sql_storage\Query\ConditionSql.

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 minus one, because one element is the the
   * conjunction.
   */
  public function count();

  /**
   * Adds a condition.
   *
   * @param string|\Drupal\Core\Entity\Query\ConditionInterface $field
   * @param mixed $value
   * @param string $operator
   * @param string $langcode
   * @return ConditionInterface
   * @see \Drupal\Core\Entity\Query\QueryInterface::condition()
   */
  public function condition($field, $value = NULL, $operator = NULL, $langcode = NULL);

  /**
   * Queries for the existence of a field.
   *
   * @param $field
   * @param string $langcode
   * @return ConditionInterface
   * @see \Drupal\Core\Entity\Query\QueryInterface::exists()
   */
  public function exists($field, $langcode = NULL);

  /**
   * Queries for the existence of a field.
   *
   * @param string $field
   * @return ConditionInterface;
   * @see \Drupal\Core\Entity\Query\QueryInterface::notexists()
   */
  public function notExists($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);

}