trait InsertTrait in Drupal 8

trait InsertTrait {

  /**
   * The table on which to insert.
   *
   * @var string
   */
  protected $table;

  /**
   * An array of fields on which to insert.
   *
   * @var array
   */
  protected $insertFields = [];

  /**
   * An array of fields that should be set to their database-defined defaults.
   *
   * @var array
   */
  protected $defaultFields = [];

  /**
   * A nested array of values to insert.
   *
   * $insertValues is an array of arrays. Each sub-array is either an
   * associative array whose keys are field names and whose values are field
   * values to insert, or a non-associative array of values in the same order
   * as $insertFields.
   *
   * Whether multiple insert sets will be run in a single query or multiple
   * queries is left to individual drivers to implement in whatever manner is
   * most appropriate. The order of values in each sub-array must match the
   * order of fields in $insertFields.
   *
   * @var array
   */
  protected $insertValues = [];

  /**
   * Adds a set of field->value pairs to be inserted.
   *
   * This method may only be called once. Calling it a second time will be
   * ignored. To queue up multiple sets of values to be inserted at once,
   * use the values() method.
   *
   * @param array $fields
   *   An array of fields on which to insert. This array may be indexed or
   *   associative. If indexed, the array is taken to be the list of fields.
   *   If associative, the keys of the array are taken to be the fields and
   *   the values are taken to be corresponding values to insert. If a
   *   $values argument is provided, $fields must be indexed.
   * @param array $values
   *   (optional) An array of fields to insert into the database. The values
   *   must be specified in the same order as the $fields array.
   *
   * @return $this
   *   The called object.
   */
  public function fields(array $fields, array $values = []) {
    if (empty($this->insertFields)) {
      if (empty($values)) {
        if (!is_numeric(key($fields))) {
          $values = array_values($fields);
          $fields = array_keys($fields);
        }
      }
      $this->insertFields = $fields;
      if (!empty($values)) {
        $this->insertValues[] = $values;
      }
    }
    return $this;
  }

  /**
   * Adds another set of values to the query to be inserted.
   *
   * If $values is a numeric-keyed array, it will be assumed to be in the same
   * order as the original fields() call. If it is associative, it may be
   * in any order as long as the keys of the array match the names of the
   * fields.
   *
   * @param array $values
   *   An array of values to add to the query.
   *
   * @return $this
   *   The called object.
   */
  public function values(array $values) {
    if (is_numeric(key($values))) {
      $this->insertValues[] = $values;
    }
    elseif ($this->insertFields) {

      // Reorder the submitted values to match the fields array.
      foreach ($this->insertFields as $key) {
        $insert_values[$key] = $values[$key];
      }

      // For consistency, the values array is always numerically indexed.
      $this->insertValues[] = array_values($insert_values);
    }
    return $this;
  }

  /**
   * Specifies fields for which the database defaults should be used.
   *
   * If you want to force a given field to use the database-defined default,
   * not NULL or undefined, use this method to instruct the database to use
   * default values explicitly. In most cases this will not be necessary
   * unless you are inserting a row that is all default values, as you cannot
   * specify no values in an INSERT query.
   *
   * Specifying a field both in fields() and in useDefaults() is an error
   * and will not execute.
   *
   * @param array $fields
   *   An array of values for which to use the default values
   *   specified in the table definition.
   *
   * @return $this
   *   The called object.
   */
  public function useDefaults(array $fields) {
    $this->defaultFields = $fields;
    return $this;
  }

  /**
   * Returns the query placeholders for values that will be inserted.
   *
   * @param array $nested_insert_values
   *   A nested array of values to insert.
   * @param array $default_fields
   *   An array of fields that should be set to their database-defined defaults.
   *
   * @return array
   *   An array of insert placeholders.
   */
  protected function getInsertPlaceholderFragment(array $nested_insert_values, array $default_fields) {
    $max_placeholder = 0;
    $values = [];
    if ($nested_insert_values) {
      foreach ($nested_insert_values as $insert_values) {
        $placeholders = [];

        // Default fields aren't really placeholders, but this is the most convenient
        // way to handle them.
        $placeholders = array_pad($placeholders, count($default_fields), 'default');
        $new_placeholder = $max_placeholder + count($insert_values);
        for ($i = $max_placeholder; $i < $new_placeholder; ++$i) {
          $placeholders[] = ':db_insert_placeholder_' . $i;
        }
        $max_placeholder = $new_placeholder;
        $values[] = '(' . implode(', ', $placeholders) . ')';
      }
    }
    else {

      // If there are no values, then this is a default-only query. We still need to handle that.
      $placeholders = array_fill(0, count($default_fields), 'default');
      $values[] = '(' . implode(', ', $placeholders) . ')';
    }
    return $values;
  }

  /**
   * {@inheritdoc}
   */
  public function count() {
    return count($this->insertValues);
  }

}