is this tricky in linq? Regex with Linq combo

Question

I have a model with a property string that can be the format "00000044" so assuming I'm querying a List of

public class Foo
{
     private string MemberNo { get; set; }
}

populated from Entity Framework,

and our set includes the following:

"00000044" include this
"44000000" include this
"20440000" exclude this

how to write a query that will exclude anything with non-zero number to the left of our search criteria "44"

Is it possible to combine Regex with linq or is there a smarter way?

Ta

How about `0*44`? Matches none or any amount of zeros and then 44. You can also do `foo.MemberNo.TrimStart('0').StartsWith("44")` to see if the "44" is the first non-zero match. — SimpleVar, May 29 '12 at 03:09
hey thanks for response. could you show me the linq query? We're ok with the 0*44 regex - just how to write the query - i forgot to add this is querying EF - apolz. — MikeW, May 29 '12 at 03:10
Read about the LIKE keyword in SQL queries, because you don't want to pull all the data and then filter it, but better filter it DB-wise. — SimpleVar, May 29 '12 at 03:12

score 6 · Accepted Answer · edited May 23 '17 at 12:20

6

var filteredFoos = myFoos
    .Where(foo => foo.MemberNo.TrimStart('0').StartsWith("44"));

Now this is if you want to bring back all Foos, but if you'd like to use the Entity Framework, look at this answer to translate it correctly.

edited May 23 '17 at 12:20

Community

answered May 29 '12 at 03:15

Yuriy Faktorovich

Andrew Cooper · Answer 2 · 2012-05-29T03:23:48.603

1

var result = fooList.Where(foo => Regex.IsMatch(foo.MemberNo, @"^0*44\d*$"));

You'll also need to make the MemberNo property public.

Edit

Or alternatively, a regex-free version:

var result = fooList.Where(foo => foo.MemberNo.TrimStart('0').StartsWith("44"));

edited May 29 '12 at 03:23

answered May 29 '12 at 03:13

Andrew Cooper

I'd stay away from regex because it sounds like the 44 may be an enterable search field. – Yuriy Faktorovich May 29 '12 at 03:14
@YuriyFaktorovich In that case it's fairly easy to build a regex pattern on the fly, and if you have it in a variable with a meaningful name I think it ends up being more readable. Having said that see my edit for a regex-free version which would probably perform better if there's a lot of `Foo` to be filtered. – Andrew Cooper May 29 '12 at 03:25
@YuriyFaktorovich And then I noticed it's the same as your answer. Doh! – Andrew Cooper May 29 '12 at 03:26
This was a great answer, the answer I marked is better for my overall understanding , but I appreciate the response - this works perfectly. – MikeW May 29 '12 at 03:27

2 Answers2