[Source Code]-Relax C# LINQ String Comparison (Trim, Case Insensitive, ??)-LINQ,C#

This is a very late answer.

You can use Regex to solve your problem Here's what I have tried, hope it helps

I created a sample class

 public class SampleTable
 {
     public string Name { get; set; }

     public SampleTable(string name)
     {
        Name = name;
     }
 }

Populated sample data

List<SampleTable> sampleTblList = new List<SampleTable>();
sampleTblList.Add(new SampleTable(" Apple"));
sampleTblList.Add(new SampleTable(" APPLE"));
sampleTblList.Add(new SampleTable("Apple"));
sampleTblList.Add(new SampleTable("apple"));
sampleTblList.Add(new SampleTable("apple "));
sampleTblList.Add(new SampleTable("apmangple"));

Solution:-

string fruitName = "apple";
List<SampleTable> sortedSampleTblList = sampleTblList.Where(x => 
Regex.IsMatch(fruitName, x.Name, RegexOptions.IgnorePatternWhitespace | RegexOptions.IgnoreCase)).ToList();

Output:-

string ans = String.Join(",", sortedSampleTblList.Select(x => x.Name.Replace(" ","_")).ToArray());
Console.Write(ans);

_Apple,_APPLE,Apple,apple,apple_

fruitsTable.Where(row => row.name.Trim().Equals(fruitname, StringComparison.OrdinalIgnoreCase)); should do what you need, but I'm confused because you've listed almost the same under Issue 3. Were you not realising it was working because you are reusing fruits2?

This little NUnit test is passing

[Test]
public void FruitTest()
{
    var fruitsTable = new List<string> { " Apple", " APPLE", "Apple", "apple", "apple ", " apple", "APPLE " };
    var fruitname = "apple ".Trim();

    var fruits = fruitsTable.Where(row => row.Trim().Equals(fruitname, StringComparison.OrdinalIgnoreCase));

    Assert.AreEqual(fruitsTable.Count(), fruits.Count());
}

Here's a nice String Extension method that builds on the solutions from a similiar question about casing StackOverflow

Keep in mind, we want to allow for NULL strings in our trim scenarios, so this extension will do a Case Insensitive compare on Trimmed strings after checking for null values

public static class StringExtension
{
    // Trim strings and compare values without casing
    public static bool SqlCompare(this string source, string value)
    {
        // Handle nulls before trimming
        if (!string.IsNullOrEmpty(source))
            source = source.Trim();

        if (!string.IsNullOrEmpty(value))
            value = value.Trim();

        // Compare strings (case insensitive)
        return string.Equals(source, value, StringComparison.CurrentCultureIgnoreCase);
    }
}

Here's how to use the Extension in your LINQ statement:

(SysUserDisplayFavorites table is composed of char() fields with space filled results. These will get trimmed and compared (case insensitive) to the user provided values in displayFavorite object)

                    var defaultFavorite = _context.SysUserDisplayFavorites
                    .Where(x => x.UserId.SqlCompare(displayFavorite.UserId))
                    .Where(x => x.ModuleCode.SqlCompare(displayFavorite.ModuleCode))
                    .Where(x => x.ActivityCode.SqlCompare(displayFavorite.ActivityCode))
                    .Where(x => x.ActivityItemCode.SqlCompare(displayFavorite.ActivityItemCode))
                    .Where(x => x.IsDefault);