unique 验证与图片的 require 验证无法共赢，大家看看 [ 2.0 版本 ]

model：

public $imageFile;
public function rules()
{
    return [
        [['name','cat','SKU','imageFile'], 'required'],
        [['cat','name', 'photo', 'SKU',], 'string', 'max' => 100],
        ['photo','safe','on'=>'update'],
        ['SKU', 'unique', 'message' => '产品编码已存在.'],
        ['imageFile', 'image', 'extensions' => 'png, jpg',
            'minWidth' => 100, 'maxWidth' => 1500,
            'minHeight' => 100, 'maxHeight' => 1000,
        ],
    ];
}

controller：

public function actionCreate() {
    $model = new Product();
    //unique的ajax验证
    if (Yii::$app->request->isAjax && $model->load(Yii::$app->request->post())) {
        Yii::$app->response->format = Response::FORMAT_JSON;
        return ActiveForm::validate($model);
    }
    if ($model->load(Yii::$app->request->post())  ) {
        $model->imageFile = UploadedFile::getInstance($model, 'imageFile');
        $filename = '/uploads/product/' . time() . uniqid() . '.' . $model->imageFile->extension;
        $path = Yii::$app->basePath . $filename;
        $model->photo = $filename;
        //$model->validate();
        if ( $model->save()) {
            $model->imageFile->saveAs($path);
            return $this->redirect(['view', 'id' => $model->id]);
        }else{
            return $this->render('create', [
                'model' => $model,
            ]);
        }
    } else {
        return $this->render('create', [
                    'model' => $model,
        ]);
    }
}

view：

.....
<?php $form = ActiveForm::begin(['id'=>'create-from',
    'layout'=>'horizontal', 
    //据查unique验证必须开这个
    'enableAjaxValidation' => true]);
?>

<?php echo $form->errorSummary($model); ?>
<div class="form-group">
    <?php echo Html::submitButton('新建产品', ['class' =>  'btn btn-lg  btn-success']) ?>
</div>

<?php echo $form->field($model, 'name')->textInput(['maxlength' => true]) ?>
<?php echo $form->field($model, 'cat')->dropDownList( yii\helpers\ArrayHelper::map(\common\models\ArticleCategory::findBySql('select title from article_category')->all(), 'title', 'title'), ['prompt' => '---请选择---']) ?>
<?php //echo $form->field($model, 'cat')->textInput(['maxlength' => true]) ?>
<?php echo $form->field($model, 'imageFile')->fileinput(['maxlength' => true]) ?>
......