[EDITED 2]

I'm having a hard time sorting by "topicCount" which is defined as a relational getter on the "Tag" model. A topic can have many tags and wants to sort the tags by the number of topics that contain that tag.

In my models /Tag.php:

public function getTopicCount()
{
    return TopicTag::find()->where(['tag_id' => $this->id])->count();
}

      

        
        
        
      

    

And in my views /tag/index.php:

<?= GridView::widget([
    'dataProvider' => $dataProvider,
    'columns' => [
        'id',
        'name',
        [
             'attribute'=>'topicCount',
             'value' => 'topicCount',
        ],
        'created_at',

        ['class' => 'yii\grid\ActionColumn','template' => '{view}',],
    ],
]); ?>

      

        
        
        
      

    

And in my controllers /TagController.php:

public function actionIndex()
{
    $dataProvider = new ActiveDataProvider([
        'query' => Tag::find(),
        'sort'=> [
            'defaultOrder' => ['id'=>SORT_DESC],
            'attributes' => ['id','topicCount'],
        ],
        'pagination' => [
            'pageSize' => 100,
        ],
    ]);

    return $this->render('index', [
        'dataProvider' => $dataProvider,
    ]);
}

      

        
        
        
      

    

And in my models /TagSearch.php:

<?php

namespace common\models;

use Yii;

/**
 * This is the model class for table "tags".
 *
 * @property integer $id
 * @property string $name
 * @property string $created_at
 * @property string $updated_at
 */
class TagSearch extends Tag
{

public $topicCount;

/**
 * @inheritdoc
 */
public function rules()
{
    return [
        [['topicCount'], 'safe']
    ];
}

public function search($params)
{
    // create ActiveQuery
    $query = Tag::find();
    $query->joinWith(['topicCount']);

    $dataProvider = new ActiveDataProvider([
        'query' => $query,
    ]);

    $dataProvider->sort->attributes['topicCount'] = [
        'asc' => ['topicCount' => SORT_ASC],
        'desc' => ['topicCount' => SORT_DESC],
    ];

    if (!($this->load($params) && $this->validate())) {
        return $dataProvider;
    }

    $query->andFilterWhere([
        //... other searched attributes here
    ])
    ->andFilterWhere(['=', 'topicCount', $this->topicCount]);

    return $dataProvider;
}


}

      

        
        
        
      

    

And in the index view I see the correct topicCount:

but clicking on topicCount column shows error:

exception 'PDOException' with message 'SQLSTATE[42703]: Undefined column: 7 ERROR: column "topicCount" does not exist LINE 1: SELECT * FROM "tags" ORDER BY "topicCount" LIMIT 100

Thanks for any recommendations ..!

[EDIT]

Following Lucas's advice, I have set my dataProvider request in my $ dataProvider like this:

'query' => $query->select(['tags.*','(select count(topic_tags.id) from topic_tags where topic_tags.tag_id=tags.id) topicCount'])->groupBy('tags.id'),

      

        
        
        
      

    

and I got the error:

exception 'PDOException' with message 'SQLSTATE[42P01]: Undefined table: 7 ERROR: missing FROM-clause entry for table "tags"

so I reformulated like this:

        'query' => $query->from('tags')->leftJoin('topic_tags','topic_tags.tag_id = tags.id')->select(['tags.*','(select count(topic_tags.id) from topic_tags where topic_tags.tag_id=tags.id) topicCount'])->groupBy('tags.id'),

      

        
        
        
      

    

and now i get the result:

obviously the topicCount column is not set, so when I try to sort it it returns an error:

exception 'PDOException' with message 'SQLSTATE[42703]: Undefined column: 7 ERROR: column "topicCount" does not exist

but when I try to execute SQL directly in DB it works fine:

so my guess is that the problem is how Yii handles the "topicCount" alias?

2nd EDIT

Still the same result without the topicCount parameter set in the Grid view. I'll show my TagSearch model, TagController and views / tags / index file below:

TagSearch

<?php

namespace common\models;

use Yii;
use yii\base\Model;
use yii\data\ActiveDataProvider;
use common\models\Tag;

/**
 * TagSearch represents the model behind the search form about `common\models\Tag`.
 */
class TagSearch extends Tag
{

    public $topicCount;

    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            [['id', 'topicCount'], 'integer'],
            [['name', 'created_at', 'updated_at', 'topicCount'], 'safe'],
        ];
    }

    /**
     * @inheritdoc
     */
    public function scenarios()
    {
        // bypass scenarios() implementation in the parent class
        return Model::scenarios();
    }

    /**
     * Creates data provider instance with search query applied
     *
     * @param array $params
     *
     * @return ActiveDataProvider
     */
    public function search($params)
    {
        $query = Tag::find();

        $dataProvider = new ActiveDataProvider([
            'query' => $query->from("tags")->select(["tags.*","(select count(topic_tags.id) from topic_tags where topic_tags.tag_id=tags.id) topicCount"])->groupBy("tags.id"),
        ]);

        $this->load($params);

        if (!$this->validate()) {
            // uncomment the following line if you do not want to return any records when validation fails
            $query->where('0=1');
            return $dataProvider;
        }

        $query->andFilterWhere([
            'id' => $this->id,
            'topicCount' => $this->topicCount,
            'created_at' => $this->created_at,
            'updated_at' => $this->updated_at,
        ]);

        $query->andFilterWhere(['like', 'name', $this->name]);

        return $dataProvider;
    }
}

      

        
        
        
      

    

Tag Model

<?php

namespace common\models;

use Yii;

/**
 * This is the model class for table "tags".
 *
 * @property integer $id
 * @property integer $topicCount
 * @property string $name
 * @property string $created_at
 * @property string $updated_at
 */
class Tag extends \yii\db\ActiveRecord
{

    public $topicCount;

    /**
     * @inheritdoc
     */
    public static function tableName()
    {
        return 'tags';
    }

    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            [['topicCount'], 'integer'],
            [['name'], 'string'],
            [['created_at', 'updated_at'], 'required'],
            [['created_at', 'updated_at'], 'safe']
        ];
    }

    /**
     * @inheritdoc
     */
    public function attributeLabels()
    {
        return [
            'id' => 'ID',
            'name' => 'Name',
            'topicCount' => 'TC',
            'created_at' => 'Created At',
            'updated_at' => 'Updated At',
        ];
    }

}

      

        
        
        
      

    

TagController

public function actionIndex()
{

    $searchModel = new TagSearch();
    $myModels = $searchModel->search([]);

    return $this->render('index', [
        'dataProvider' => $myModels,
    ]);
}

      

        
        
        
      

    

labels / index

<?= GridView::widget([
    'dataProvider' => $dataProvider,
    'columns' => [
        'id',
        'name',
        'topicCount',
        'created_at',
        'updated_at',
        ['class' => 'yii\grid\ActionColumn','template' => '{view}',],
    ],
]); ?>

      

        
        
        
      

    

What am I missing?