Linq result fails when checking for null value for column.

Question

User-2054057000 posted

Why this Linq query fails?

string blogCategoryId=null;
var r1 = context.Blog.Where(x => (blogCategoryId != null && x.CategoryId == blogCategoryId)).ToList();

I want this query should return all blogs without where condition since blogCategoryId is null. 

But this query return 0 records stating the where condition x.CategoryId == blogCategoryId has been applied?

Why it is so?

Answer 1

User-821857111 posted

string blogCategoryId=null;
var r1 = context.Blog.Where(x => (blogCategoryId != null && x.CategoryId == blogCategoryId)).ToList();

The condition "blogCategory != null" will always be false. Therefore no records will ever be returned.

Answer 2

User-2054057000 posted

Mikesdotnetting

yogyogi

string blogCategoryId=null;
var r1 = context.Blog.Where(x => (blogCategoryId != null && x.CategoryId == blogCategoryId)).ToList();

The condition "blogCategory != null" will always be false. Therefore no records will ever be returned.

Actually I want my condition to work this way.

1. If blogCategoryId is null then apply no check in where and return context.blog.
2. if blogCategoryId is not null then apply check in where and return context.blog(x=>x. CategoryId==blogCategoryId);

How to do it?

Answer 3

User-821857111 posted

var r1 = context.Blog.Where(x => (blogCategoryId == null || x.CategoryId == blogCategoryId)).ToList();

Answer 4

User-2054057000 posted

Thanks, knew the problem which I was doing. Thank you!