Yii2 Model search query - yii2

Question

How can I add where condition to my Articles model so that slug(From category model) is equal to $slug?
And this is a function that Gii generated:
public function getCategory()
{
return $this->hasOne(Categories::className(), ['id' => 'category_id']);
}
Here's my code:
public function specificItems($slug)
{
$query = Articles::find()->with('category');
$countQuery = clone $query;
$pages = new Pagination(['totalCount' => $countQuery->count(),'pageSize' => 12]);
$articles = $query->offset($pages->offset)
->limit($pages->limit)
->all();
return ['articles' => $articles,'pages' => $pages];
}

Answer 1

Your SQL query should contain columns from both article and category table. For that you need to use joinWith().
$result = Articles::find()
->joinWith('category')
->andWhere(['category.slug' => $slug])
->all();
Where 'category' is then name of your category table.
However, in your code you deviate from certain best practices. I would recommend the following:
Have both table name and model class in singular (Article and article). A relation can be in plural, like getCategories if an article has multiple categories.
Avoid functions that return result sets. Better return ActiveQuery class. If you have a query object, all you need to get the actual models is ->all(). However, you can further manipulate this object, add more conditions, change result format (->asArray()) and other useful stuff. Returning array of results does not allow that.
Consider extending ActiveQuery class into ArticleQuery and implementing conditions there. You'll then be able to do things like Article::find()->joinWith('category')->byCategorySlug('foo')->all().