A helper function using yii\db\BaseActiveRecord::getRelation() to get relation type + optional check if both models are related on DB if respective ids are provided

relationInfo.php

<?php

private function relationInfo($model, $name, $related_id = false)
{
    $relation = $model->getRelation($name, false);
    if ($relation === null) return null;

    $info = [];

    $info['class'] = $relation->modelClass;

    if ($relation->multiple === true && $relation->via === null) $info['type'] = 'is_child';
    else if ($relation->multiple === true) $info['type'] = 'many_many';
    else $info['type'] = 'is_parent';

    $pk = implode(',', array_values($model->tableSchema->primaryKey));
    $info['key'] = $info['type'] === 'is_child' ? null : $relation->link[$pk];

    if ($related_id) {

        if ($model->getIsNewRecord()) 
            throw new \yii\base\InvalidCallException('Unable to check relation. model is not yet saved.');

        if ($info['type'] == 'is_parent') 
            $info['related'] = isset($model->{$info['key']}) && $model->{$info['key']} === (int)$related_id;

        if ($info['type'] == 'many_many')
            $info['related'] = (new \yii\db\Query())
                ->from(reset($relation->via->from))
                ->where([ key($relation->via->link) => $model->id, $info['key'] => $related_id ])
                ->exists();
    }

    return $info;
}

// Examples :
$tag   = Tag::findOne(1);
$image = Image::findOne(2); 
$owner = Owner::findOne(1); 

$this->relationInfo($tag, 'images', 2);
/** Output :
 *  {
 *    "class": "\app\models\Image",
 *    "type": "many_many",
 *    "key": "image_id",
 *    "related": true
 *  },
*/

$this->relationInfo($image, 'tags', 1);
/** Output :
 *  {
 *    "class": "\app\models\Tag",
 *    "type": "many_many",
 *    "key": "tag_id",
 *    "related": true
 *  },
*/

$this->relationInfo($tag, 'owner', 1);
/** Output : null, **/


$this->relationInfo($owner, 'tags', 1);
/** Output : null, **/

$this->relationInfo($image, 'owner', 1);
/** Output :
 *  {
 *    "class": "\app\models\Owner",
 *    "type": "is_parent",
 *    "key": "owner_id",
 *    "related": false
 *  },
*/

$this->relationInfo($owner, 'images', 1);
/** Output :
 *  {
 *    "class": "\app\models\Image",
 *    "type": "is_child",
 *    "key": null
 *  }
*/