error in LINQ while converting IPaddress to String using C# and PostgreSQL database

Question

How to convert IPAddress to String is not that enough to use .ToString()? I do it in LINQ and I get :

Object reference not set to an instance of an object

here is my code:

 var x = (from t in db.v_vpn_gateway.AsEnumerable()

                 select new TurbineDvce
                 {
                     Comments = "VPN Gateway",
                     Description = string.Empty,
                     DeviceType = t.device_type,                                              
                     TurbineId = t.turbine_id.ToString(),
                     Username = string.Empty
                 })

TurbineId is string

because t.turbine_id is null so you can't add .ToString() Do a null check, then add .ToString — mb14, May 21 '20 at 08:19
Does this answer your question? [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) — Selim Yildiz, May 21 '20 at 08:22
@GuruStron in .Net Core i get an error stating multiple connection at the same time to database,then i found on the internet its better to apply the condition after converting to AsEnumerable — moris62, May 21 '20 at 08:26
@mortezasol there should be no problems with having multiple connection at the same time to postgres. Conditions i general should not by applied after `AsEnumerable` cause `AsEnumerable` will fetch whole table into memory. As for projection - it depends on how many column you actually need. — Guru Stron, May 21 '20 at 08:33
@GuruStron thanks for the advice,but whats the reason its said,in .NetCore the query is done on the server side,so sometimes it has a problem with union and other conditions if you apply ,beuacse it cant transalte it on the server side,thats why it should be converted to AsEnumerable,whats your idea? — moris62, May 21 '20 at 08:40
@mortezasol it was not evident from you example that you was resolving such problems. Have you tried the null check? — Guru Stron, May 21 '20 at 08:44
@GuruStron if i dont convert to AsEnumerable how should i check if its null or emtry,if its not null then convert it to string. — moris62, May 21 '20 at 08:46
@mortezasol you will need to check, but i would say you will not need to, if db can handle conversion from type of `turbine_id` to string(nvarchar) then it just will put nulls in your string. — Guru Stron, May 21 '20 at 08:48
@GuruStron you are right,but i dont have a control over the DB otherwise i would ask them(other team) to do it — moris62, May 21 '20 at 08:49
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/214319/discussion-between-guru-stron-and-mortezasol). — Guru Stron, May 21 '20 at 08:50

score 0 · Answer 1 · answered May 21 '20 at 08:21

0

Because t.turbine_id is null so you can't add .ToString() Do a null check, then add .ToString()

TurbineId = t.turbine_id ?? t.turbine_id.ToString()

answered May 21 '20 at 08:21

mb14

460
4
15

Since `AsEnumerable()` is called you can just `t.turbine_id?.ToString()` – Guru Stron May 21 '20 at 08:22
?? cant apply to operand IPAddress and string – moris62 May 21 '20 at 08:47
So `TurbineId` is of what type? – mb14 May 21 '20 at 08:51
its string but t.turbine_id is Ipadress – moris62 May 21 '20 at 08:56
how should i check if IPaddress is null or empty? – moris62 May 21 '20 at 09:26

error in LINQ while converting IPaddress to String using C# and PostgreSQL database

1 Answers1