think\Model::belongsTo PHP Method

    public function belongsTo($model, $foreignKey = '', $otherKey = '', $alias = [], $joinType = 'INNER')
    {
        // 记录当前关联信息
        $model = $this->parseModel($model);
        $foreignKey = $foreignKey ?: Loader::parseName(basename(str_replace('\\', '/', $model))) . '_id';
        $otherKey = $otherKey ?: (new $model())->getPk();
        return $this->relation()->belongsTo($model, $foreignKey, $otherKey, $alias, $joinType);
    }