Laravel eloquent model method to enable save with composite primary key

CustomModel.php

    /**
     * Set the composite keys for a save update query.
     *
     * @param  \Illuminate\Database\Eloquent\Builder  $query
     * @return \Illuminate\Database\Eloquent\Builder
     */
    protected function setKeysForSaveQuery(Builder $query)
    {
        $query
            ->where('user_id', '=', $this->getAttribute('user_id'))
            ->where('date', '=', $this->getAttribute('date'))
            ->where('slot', '=', $this->getAttribute('slot'));
        return $query;
    }