在yii2中找不到类'common \ models \ LinkAllBehavior'是什么？

While I am testing yii2 multiple select2 tutorial, I faced the error "Class 'common\models\LinkAllBehavior' not found".

Here is my model code,

public $tag_ids;
public static function tableName()
{
    return 'post';
}

public function rules()
{
    return [
        [['title', 'body','tag_ids'], 'required'],
        [['body'], 'string'],
        [['title'], 'string', 'max' => 255],
    ];
}
public function attributeLabels()
{return [
        'id' => 'ID',
        'title' => 'Title',
        'body' => 'Body',
    ];}

public function behaviors()
{
    return [
        LinkAllBehavior::className(),
    ];
}

public function afterSave($insert, $changedAttributes)
{
    $tags = [];
    foreach ($this->tag_ids as $tag_name) {
        $tag = Tag::getTagByName($tag_name);
        if ($tag) {
            $tags[] = $tag;
        }
    }
    $this->linkAll('tags', $tags);
    parent::afterSave($insert, $changedAttributes);
}

public function getPostToTags()
{
    return $this->hasMany(PostToTag::className(), ['post_id' => 'id']);
}

public function getTags()
{
    return $this->hasMany(Tag::className(), ['id' => 'tag_id'])->viaTable('post_to_tag', ['post_id' => 'id']);
}

}

So, I would like to know what is LinkAllBehavior and how does it work?

Thanks

LinkAllBehavior::className()

above line is causing this, if you are using yii2-linkall

try adding

use cornernote\linkall\LinkAllBehavior;

on top of your model code along with other use statements