unable to get result showing Object reference not set to an instance of an object

Question

i want get last record of table with particular column value. after that i need to increment value ..here table is empty and column propery is string

     public async Task<string> GetLastBillNo()
            {
                return this.DbSet.LastOrDefault().CustomOrderNumber;
            } // getting Object reference not set to an instance of an object”

bs logic is

 long billNo = 0;

     if (!string.IsNullOrEmpty(await invoiceRepository.GetLastBillNo()))
                    {
                        billNo = long.Parse(await invoiceRepository.GetLastBillNo());
                        billNo = billNo + 1;
                        order.CustomOrderNumber = billNo.ToString();
                    }
                    else
                        order.CustomOrderNumber = (billNo + 1).ToString();

Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Ňɏssa Pøngjǣrdenlarp, Sep 14 '19 at 16:39

score 3 · Answer 1 · answered Sep 16 '19 at 14:32

You need to check the null Object reference before incrementing the next value.

        public async Task<string> GetLastBillNo()
        {
            return (this.DbSet.LastOrDefault() != null ? this.DbSet.LastOrDefault().CustomOrderNumber : string.Empty);
        }

score 0 · Answer 2 · answered Sep 14 '19 at 16:57

0

Is order class static ? Else, You need to instantiate the order object. It does not exist inside the context.

answered Sep 14 '19 at 16:57

TropicalViking

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2
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no TropicalViking its an entity ..its contain one of the filed "CustomOrderNumber " – user2564537 Sep 14 '19 at 16:59

score 0 · Answer 3 · answered Sep 14 '19 at 17:18

using (var order = new YourDBContext()) {
        if (!string.IsNullOrEmpty(await invoiceRepository.GetLastBillNo()))
                {
                    billNo = long.Parse(await invoiceRepository.GetLastBillNo());
                    billNo = billNo + 1;
                    order.CustomOrderNumber = billNo.ToString();
                }
                else
                    order.CustomOrderNumber = (billNo + 1).ToString();
...rest of your code
    }

unable to get result showing Object reference not set to an instance of an object

3 Answers3