LINQ Filter values on list values using contain

Question

I know that there are several SO posts on this matter and I have used them when coming up with my current solution.

Looking at the 4 rows of code below, the first three are not working but the forth one is (!?) and I do not understand why that is. The first two only checks against a single string: "Where values that contains 'string'", and the later two checks values against a list of strings "Where values that contain any of the strings in this list"

contactsDynamicResponses.Values.Where(cdr => cdr.Firstname.Contains(firstName)).ToList();
contactsDynamicResponses.Values.Where(cdr => cdr.Lastname.Contains(lastName)).ToList();

contactsDynamicResponses.Values.Where(cdr => accountIdsList.Any(ail => cdr.AccountId.Contains(ail))).ToList();
contactsDynamicResponses.Values.Where(cdr => contactIdsList.Any(cil => cdr.ContactId.Contains(cil))).ToList();

My goal is to filter the list depending on the search filters entered into the function. Below is the error I get, which makes me think there is something about the contactsDynamicResponses.Values that is the problem here, but I am lost.

System.NullReferenceException: 'Object reference not set to an instance of an object.' Project.Entities.Contact.Models.Dynamics.ContactDynamicsResponse.Firstname.get returned null.

How the rows look completely:

contactsDynamicResponses.Values = string.IsNullOrEmpty(firstName) ? contactsDynamicResponses.Values : contactsDynamicResponses.Values.Where(cdr => cdr.Firstname.Contains(firstName)).ToList();
contactsDynamicResponses.Values = string.IsNullOrEmpty(lastName) ? contactsDynamicResponses.Values : contactsDynamicResponses.Values.Where(cdr => cdr.Lastname.Contains(lastName)).ToList();
           
contactsDynamicResponses.Values = accountIdsList == null ? contactsDynamicResponses.Values : contactsDynamicResponses.Values.Where(cdr => accountIdsList.Any(ail => cdr.AccountId.Contains(ail))).ToList();
contactsDynamicResponses.Values = contactIdsList == null ? contactsDynamicResponses.Values : contactsDynamicResponses.Values.Where(cdr => contactIdsList.Any(cil => cdr.ContactId.Contains(cil))).ToList();

Any thoughts are welcome! Thank you!

Seems you should add null-checks before calling Contains on FirstName and LastName because these properties can get null and cause your exception here — Flat Eric
– Flat Eric, Commented Mar 22, 2021 at 13:02
The exception already tells you exactly what the problem is: ContactDynamicsResponse.Firstname.get returned null.. So Firstname is null and you are calling .Contains() on a string which is null so therefore you get a NullReferenceException — Nannanas
– Nannanas, Commented Mar 22, 2021 at 13:04

Flat Eric · Accepted Answer · 2021-03-22 13:04:04Z

1

Add null-checks in the query:

contactsDynamicResponses.Values.Where(cdr => cdr.Firstname != null && 
    cdr.Firstname.Contains(firstName)).ToList();

The exception says that FirstName is null.
Also add this check in the other queries, for example for LastName

answered Mar 22, 2021 at 13:04

Flat Eric

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1 Comment

FearlessFox Over a year ago

Aaah, of course! It didn't occur to me that cdr.FirstName could be null (even though it was spelled out). Thank you for making my day :)

Charlieface · Accepted Answer · 2021-03-22 14:38:58Z

0

A shorter way to do a null-check:

contactsDynamicResponses.Values.Where(cdr =>
    cdr.Firstname?.Contains(firstName) == true
).ToList();

It looks a bit odd with the == true but that is because the result of the comparison is bool?

answered Mar 22, 2021 at 14:38

Charlieface

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