Search string within a string array in a LINQ expression

Question

if (!string.IsNullOrEmpty(Queries["SurnameInitial"]))
{
    var initials = Queries["SurnameInitial"].Split(',').ToList();
        filter.And(s => initials.Contains(s.Surname.ToArray()[0].ToString()));
}

It throws exception

LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression.

How can i match char vs string?

Because it couldn't be translated to T-SQL, Linq to Entities couldn't recognize it. Read more stackoverflow.com/a/34061692/2946329 — Salah Akbari
– Salah Akbari, Commented Dec 20, 2016 at 10:23
I understand from Thomas' answer that s.Surname.ToArray()[0] is a char. The Linq namespace contains an extension on IEnumerables Contains(char); is that usable? Alternatively, could you use IndexOf(char) and test for != -1? — Peter - Reinstate Monica
– Peter - Reinstate Monica, Commented Dec 20, 2016 at 10:31

Thomas Ayoub · Accepted Answer · 2016-12-20 14:37:51Z

8

You can use the following s.Surname.First() instead:

if (!string.IsNullOrEmpty(Queries["SurnameInitial"]))
{
    var initials = Queries["SurnameInitial"].Split(',');
        filter.And(s => initials.Contains(s.Surname.First()));
}

This happens because Linq to Entities doesn't know what to do with char.ToString()

Since you're dealing with a List<string> you can use:

filter.And(s => initials.Any(x => x.Contains(s.Surname.First()));

edited Dec 20, 2016 at 14:37

answered Dec 20, 2016 at 10:23

Thomas Ayoub

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3 Comments

s.k.paul Over a year ago

How can i match char and string?

Thomas Ayoub Over a year ago

@s.k.paul what do you mean?

s.k.paul Over a year ago

initials is a List<string> whereas s.Surname.First() returns a char. How can I compare them?

s.k.paul · Accepted Answer · 2016-12-21 03:54:44Z

2

The following code solved my problem-

 var initials = Queries["SurnameInitial"].Split(',').ToList();
 filter.And(s => initials.Contains(s.Surname.Substring(0, 1)));

answered Dec 21, 2016 at 3:54

s.k.paul

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