How to find a number into a string from a string using LINQ?

Question

I have this string "1,2,3,4,5,6,7,8,9,10" and I want to know if any number is in a table of database.

Example

Entity

public class MyNumber {
     public string Numbers {get;set;}
}

MyNumber n = new MyNumber();
n.Numbers = "1,2,3,4,";

MyNumber n1 = new MyNumber();
n.Numbers = "5,6,7,8,9,10,"

context.MyNumbers.Add(n, n1);
context.SaveChanges();

//find numbers from a string of numbers
string _numbers = "10,11,12,15,"

//how to ?
var _myNum = context.MyNumbers.Where
.Select(x => x.Split(new string[]{","},StringSplitOptions.RemoveEmptyEntries))
.Where(x => _numbers.Split(new string[]{","},StringSplitOptions.RemoveEmptyEntries)
.Any(y => y.Equals(x)));

 //no results
 Debug.Writeline(_myNum.Count());

The string "_numbers" has the number 10 for example, and in database has the number "10", I would to know how could I find it using LINQ ?

Where(n => n.Numbers.Contains("10,")) making sure to include the comma so it doesn't match numbers like 100, 101, etc.. — hijinxbassist
– hijinxbassist, Commented Jul 6, 2021 at 21:41
You would need to split the string, and check for each individual number unless you wanted to match the exact string. You could also write a stored procedure to do the heavy lifting on the sql side. — hijinxbassist
– hijinxbassist, Commented Jul 6, 2021 at 21:46
Something like context.MyNumbers.Select(x => x.Split(new string[]{","},StringSplitOptions.RemoveEmptyEntries)).Where(x => _numbers.Split(new string[]{","},StringSplitOptions.RemoveEmptyEntries).Any(y => y == x)) — Hayden
– Hayden, Commented Jul 6, 2021 at 21:46
just a thought: isn't a comma separated string a terrible choice to store a List of Integers? — Franz Gleichmann
– Franz Gleichmann, Commented Jul 7, 2021 at 5:51
Please edit your question to show us exactly what you tried so that we can assist you better. — Hayden
– Hayden, Commented Jul 7, 2021 at 21:02

Pharaz Fadaei · Accepted Answer · 2021-07-07 23:22:06Z

1

It is not a good idea to store multiple values as a single comma-separated value in a database column. Read More.

Either way, the problem with your approach is that Linq to SQL does not support String.Split. You can still use Linq to Objects by calling AsEnumerable() on your DbSet. Then you can use any Linq technique you prefer.

An example:

var _myNum = context.MyNumbers
    .AsEnumerable()
    .SelectMany(x => x.Numbers.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries))
    .Intersect(_numbers.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries))
    .ToArray();

answered Jul 7, 2021 at 23:22

Pharaz Fadaei

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