foreach with where and condition if parameter exists

Question

I have a large query from which I'm trying to get data using the Where condition with the parameters StudentName and StudentSurname, which is set by the user through a search form.

If StudentName and StudentSurname has values, everything is fine, but if one of them does not have a value, then I receive nothing.

Problem is that in such case I want this foreach loop to get data anyway without the parameters that are null.

foreach (var item in innerJoinQuery.Where(item => item.StudentName == StudentName 
                                               && item.StudentSurname  == StudentSurname)

Do you mean the input values are not provided (i.e. `StudentName` is null) or the data is not there, i.e. `item.StudentName` is null? — Nisarg Shah, Oct 04 '18 at 06:07
yes. when you hit search but do not fill the search box of StudentName or StudentSurname . — David, Oct 04 '18 at 06:09
In that case you case just validate like this : string.IsNullOrEmpty(StudentName) which returns boolean value — xoxo, Oct 04 '18 at 06:10
Yes I want to return data anyway. And if one of variables is null then foreach gives nothing. But I want it to return at least all data with second option — David, Oct 04 '18 at 06:11
Kamala HB can you write foreach string complete so I can understand ? — David, Oct 04 '18 at 06:11
try this => `foreach (var item in innerJoinQuery.Where (item => (item.StudentName == null || item.StudentName == StudentName) && (item.StudentSurname == null || item.StudentSurname == StudentSurname) )` — er-sho, Oct 04 '18 at 06:12
try `item => (item.StudentName == StudentName || string.IsNullOrEmpty(StudentName )) && (item.StudentSurname == StudentSurname || string.IsNullOrEmpty(StudentSurname))` — Just code, Oct 04 '18 at 06:13
https://stackoverflow.com/questions/7438382/linq-how-to-exclude-condition-if-parameter-is-null this question has your answer — SilentCoder, Oct 04 '18 at 06:13
thanks all of you for help, I've checked Nisarg Shah solution and it suits me just fine. Thanks all! — David, Oct 04 '18 at 06:18
@David Can you first tell me which field you ant to check whether it is null or not? whether StudentName or item.StudentName ? Can you post your sample code? — xoxo, Oct 04 '18 at 06:19
Kamala HB I want to check StudentName and StudentSurname whether they have some value or not, and if they do then use them in foreach. Nisarg Shah wrote solution and it works perfect. I've checked it already. Thank you Sir — David, Oct 04 '18 at 06:21
Possible duplicate of [Linq: adding conditions to the where clause conditionally](https://stackoverflow.com/questions/10884651/linq-adding-conditions-to-the-where-clause-conditionally) — xdtTransform, Oct 04 '18 at 06:21

score 4 · Accepted Answer · answered Oct 04 '18 at 06:13

4

You could put an OR condition allowing an item to pass if one of the search parameters is null or empty. Something like:

innerJoinQuery.Where(item => 
    (string.IsNullOrWhiteSpace(StudentName) || item.StudentName == StudentName) 
    && 
    (string.IsNullOrWhiteSpace(StudentSurname) || item.StudentSurname  == StudentSurname)
)

answered Oct 04 '18 at 06:13

Nisarg Shah

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You can put every `or` condition in the separated `Where` function, will be much more readable – Fabio Oct 04 '18 at 07:41

score 4 · Answer 2 · edited Oct 04 '18 at 07:44

4

if (!string.IsNullOrEmpty(StudentName))
    innerJoinQuery = innerJoinQuery.Where(item => item.StudentName == StudentName);

if (!string.IsNullOrEmpty(StudentSurname))
    innerJoinQuery = innerJoinQuery.Where(item => item.StudentSurname == StudentSurname);

foreach (var item in innerJoinQuery)
...

edited Oct 04 '18 at 07:44

Nisarg Shah

14,151
6
34
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answered Oct 04 '18 at 06:15

kaffekopp

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I find this cleaner than Nisargs solution, easier to read, even though they're both essentially the same – Aydin Oct 04 '18 at 06:17

foreach with where and condition if parameter exists

2 Answers2