framework/validators/UniqueValidator.php
private function addComboNotUniqueError($model, $attribute)
    {
        $attributeCombo = [];
        $valueCombo = [];
        foreach ($this->targetAttribute as $key => $value) {
            if (is_int($key)) {
                $attributeCombo[] = $model->getAttributeLabel($value);
                $valueCombo[] = '"' . $model->$value . '"';
            } else {
                $attributeCombo[] = $model->getAttributeLabel($key);
                $valueCombo[] = '"' . $model->$key . '"';
            }
        }
        $this->addError($model, $attribute, $this->message, [
            'attributes' => Inflector::sentence($attributeCombo),
            'values' => implode('-', $valueCombo),
        ]);
    }
private function addComboNotUniqueError($model, $attribute)
    {
        $attributeCombo = [];
        $valueCombo = [];
        foreach ($this->targetAttribute as $key => $value) {
            if (is_int($key)) {
                $attributeCombo[] = $model->getAttributeLabel($value);
                $valueCombo[] = '"' . $model->$value . '"';
            } else {
                $attributeCombo[] = $model->getAttributeLabel($key);
                $valueCombo[] = '"' . $model->$key . '"';
            }
        }
        $this->addError($model, $attribute, $this->message, [
            'attributes' => Inflector::sentence($attributeCombo),
            'values' => implode('-', $valueCombo),
        ]);
    }
Builds and adds [[comboNotUnique]] error message to the specified model attribute.
@param \yii\base\Model $model the data model.
@param string $attribute the name of the attribute.