在更新记录中插入而不是覆盖新上传

Question

When I update a record, i.e a Contact, the attachments (images) are overwritten. How do I just insert the the newly attached images and not get the old ones be overwritten? Please see my codes below (I am using Yii 2.0 PHP framework).

Controller

public function actionUpdate($id)
{   
    $session = Yii::$app->session;
    $model = $this->findModel($id);
    $cur_businessname = $model->business_name;
    $attachment = $model->attachment;
    $files = array();

    if ($model->load(Yii::$app->request->post())) {
        $model->attachment = UploadedFile::getInstances($model, 'attachment');

        if($model->attachment) {
            if (empty($model->attachment)) {
                $model->attachment = UploadedFile::getInstance($model, 'attachment');
                $path = 'assets/images/default.png';
                $model->attachment = $path;
            } else {                
                foreach ($model->attachment as $attachment) {
                    $path = 'archive/contact/'.$attachment->baseName.'.'.$attachment->extension;
                    $count = 0;
                    {
                        while(file_exists($path)) {
                           $path = 'archive/contact/'.$attachment->baseName.'_'.$count.'.'.$attachment->extension;
                           $count++;
                        }
                    }                        
                    $attachment->saveAs($path);
                    $files[] = $path; 
                }
                $model->attachment = implode(',', $files); 
            }
        } else {
            $model->attachment = $attachment;
        } 
        //$updatedAttachments = array_push($attachment,$path); 
        //var_dump($attachment);
        //exit;

        $model->save();

        if($model->save()) {
            Yii::$app->session->setFlash('success', "Success!");
        } else {
            Yii::$app->session->setFlash('error', "Contact Creation Failed!");
        }

        $model->refresh();
        return $this->redirect(['index', 'id' => $session['user_id']]);
    } else {            
        return $this->renderAjax('update', [
            'model' => $model,
        ]);
    }
}

View

<?php
    if (!empty($model->attachment)) {
        $model->attachment = explode(',', $model->attachment);
        $file = '';
        foreach ($model->attachment as $attachment) {
            $file.= Html::img(Yii::$app->urlManager->baseUrl . '/'. $attachment, ['class'=>'file-preview-image', 'alt'=>'Attachment', 'title'=>'Attachment']).',';
        }
        echo FileInput::widget([
            'model' => $model,
            'attribute' => 'attachment[]',
            'options' => ['multiple' => true],
            'pluginOptions' => [
                'initialPreview'=>[ 
                    [$file,]
                ],
                'showCaption' => false,
                'showRemove' => false,
                'showUpload' => false,
                'browseClass' => 'btn btn-primary btn-block',
                'browseIcon' => '<i class="glyphicon glyphicon-camera"></i> ',
                'browseLabel' =>  'Attach Business Card',
                'maxFileCount' => 2,
                'allowedFileExtensions'=>['jpg','gif','png'], 
                'overwriteInitial' => true,
                'uploadAsync' => true,
                ],
            'options' => ['accept' => 'image/*', 'multiple' => true]
        ]);
    } else {
        echo FileInput::widget([
            'model' => $model,
            'attribute' => 'imageUrl[]',
            'options' => ['multiple' => true],
            'pluginOptions' => [
                'showCaption' => false,
                'showRemove' => false,
                'showUpload' => false,
                'maxFileCount' => 2,
                'browseClass' => 'btn btn-primary btn-block',
                'browseIcon' => '<i class="glyphicon glyphicon-camera"></i> ',
                'browseLabel' =>  'Attach Business Card',
                'allowedFileExtensions'=>['jpg','gif','png'], 
                ],
            'options' => ['accept' => 'image/*', 'multiple' => true]
        ]);
    }
?>

I have tried array_push but it's not working. The $attachment on the 6th line of actionUpdate holds the old attachments. Now, I can't anymore use $attachment inside if ($model->load(Yii::$app->request->post())) since it's already after posting/submitting the form.

How do I just insert the newly attached files without overwriting the old ones? Your comments/answers will be of great help!