How to use Contains() function if field value is null in linq

Question

I am working on a project where I use Linq for fetching data. Now I have a scenario where I have to check field value contains given string for that I use Contains() function.

Everything works fine, But when any of the field is null then it creates a problem.

personData = personData.Where(x => x.FirstName.ToLower().Contains(q.ToLower()) || x.LastName.ToLower().Contains(q.ToLower())).Select(x => x).ToList();

Here when FirstName or LastName field have a null value it throw an error.

So, how can I overcome from this problem ?

what version of c# are you using? if c#6 then null-conditional is an option. — Nkosi
– Nkosi, Commented Jan 6, 2017 at 11:42
@stomy, q is parameter to function so we can first check if(string.IsNullOrEmpty(q)) {} — Jigarb1992
– Jigarb1992, Commented Sep 17, 2019 at 6:16

Ahmar · Accepted Answer · 2017-01-06 11:39:50Z

8

Please try this

personData = personData.Where(x => (x.FirstName != null && x.FirstName.ToLower().Contains(q.ToLower())) ||  (x.LastName != null && x.LastName.ToLower().Contains(q.ToLower()))).Select(x => x).ToList();

answered Jan 6, 2017 at 11:39

Ahmar

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3 Comments

Ahmar Over a year ago

Great to help you. :)

M.kazem Akhgary Over a year ago

use named method instead of long lambda. private static bool Filter(string input, string search) {....} and then use it in Where. personData.Where(x => Filter(x, q)) @Jigarb1992

Jigarb1992 Over a year ago

please post an answer @M.kazemAkhgary

Yury Glushkov · Accepted Answer · 2017-01-06 11:39:07Z

7

Use following approach: x.FirstName?.Contains(substring) ?? false

Since C# 6 you can use null-conditional operators, that simplifies some queries greatly. You can read more about this topic here

answered Jan 6, 2017 at 11:39

Yury Glushkov

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Comments

Rahul Hendawe · Accepted Answer · 2017-01-06 12:00:45Z

4

You must check first if required values are null, Try using the null-coalescing operator...

personData = personData.Where(x => ((x.FirstName.ToLower() ?? "").Contains(q.ToLower())) ||  ((x.LastName.ToLower() ?? "").Contains(q.ToLower()))).Select(x => x).ToList();

edited Jan 6, 2017 at 12:00

answered Jan 6, 2017 at 11:48

Rahul Hendawe

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2 Comments

Jigarb1992 Over a year ago

It throw error "Operator '&&' cannot be applied to operands of type 'string' and 'bool'" @RahulHendawe

Rahul Hendawe Over a year ago

Great! it is an better way to handle such situation where if you get any null value then those values were replaced by _blank value :)

Dscoduc · Accepted Answer · 2020-06-13 22:52:58Z

1

What about using a simple string extension like the following:

public static string AsNotNull(this string value)
{
    if (string.IsNullOrWhiteSpace(value))
        return string.Empty;

    return value;
}

And then use it like:

x.FirstName.AsNotNull()

answered Jun 13, 2020 at 22:52

Dscoduc

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1 Comment

Matt Over a year ago

Likewise, to avoid null when you expect a list, you can add a 2nd extension as overload from this answer. Then, use it in the same way, i.e. .Select(x => x).AsNotNull().ToList();. With both extensions, one for strings, one for enumerables, you are well armed!

NealSinclair · Accepted Answer · 2017-01-06 11:40:42Z

-1

I think you should prevent ability to add null FirstName or LastName at the beggining. This kind of row seems unuseful.

answered Jan 6, 2017 at 11:40

NealSinclair

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2 Comments

M.kazem Akhgary Over a year ago

this is good suggestion. because if both FirstName and LastName could be null then whats the point of having names? I suggest put "" instead of null if FirstName or LastName has to be empty

Jigarb1992 Over a year ago

the code I have written in my question is just for example in actual there may be any field/s.

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