问一次为单个外键记录的Laravel多重记录

EN

    $sizes = new sizes;
    foreach($request->size as $key => $value)
    {
        $size[] = [
            'size_name' => $request->size[$key],
            'pid' => $lastid,
            'size_price' => $request->sizeprice[$key],
            'created_at' => Carbon::now(),
        ];
    }
    DB::table('sizes')->insert($size);
    $lastidsize = $sizes->id;

    $stocks = new stocks;
    foreach($request->stock as $key => $value)
    {
        $stock[] = [
            'pid' => $lastid,
            'size_id' => $lastidsize,
            'qty' => $request->stock[$key],
            'created_at' => Carbon::now(),
        ];
    }
    DB::table('stocks')->insert($stock);

**Illuminate\Database\QueryException
SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'size_id' cannot be null (SQL: insert 
into `stocks` (`created_at`, `pid`, `qty`, `size_id`) values (2021-01-24 11:40:50, 91, 1, ?), (2021- 
01-24 11:40:50, 91, 1, ?), (2021-01-24 11:40:50, 91, 1, ?))**