2 Where and 1 Group by Condition LINQ C#

Question

I need to fetch the result of the List by using 2 Where Conditions and GroupBy Condition.

The Query which worked to achive part of the solution is

 var errorQuery = AgentOpList.Where(x => x.LastError != "")
                             .GroupBy(x => x.LastError.Substring(0, 30)).ToArray();

But now, i should also include another condition in the list, so the condition is x.Status != "FINISHED" So the final query which i tried was

var errorQuery = AgentOpList.Where(x => x.LastError != "" || x.Status != "FINISHED")
                            .GroupBy(x => x.LastError.Substring(0, 30)).ToArray();

However, it throws me the error

Index and length must refer to a location within the string. Parameter name: length

I know the reason for this error. However, i would like to know the solution.

Answer 1

LastError is shorter than 30 characters.

If you're using linq to objects, you could create a new function:

public bool TakeChars(string str, int chars) {
    if (str.Length < 30) { return str; }
    else return str.Substring(0,30);
}

And then use it:

var errorQuery = AgentOpList.Where(x => x.LastError != "" || x.Status != "FINISHED")
                            .GroupBy(x => TakeChars(x.LastError, 30)).ToArray();

If you don't want to create a new function or you're using linq to sql, I think this would work (@FCin):

 var errorQuery = AgentOpList.Where(x => x.LastError != "" || x.Status != "FINISHED")
                                .GroupBy(x => x.LastError.Substring(0, Math.Min(30, x.LastError.Length))).ToArray();

Also, a small improvement to your Where :

var errorQuery = AgentOpList.Where(x => !string.IsNullOrEmpty(x.LastError) || x.Status != "FINISHED")
                                .GroupBy(x => .... ).ToArray();

Answer 2

Make sure Substring never receives a string shorter than 30 characters by padding it with trailing spaces:

var errorQuery = AgentOpList.Where(x => x.LastError != "" || x.Status != "FINISHED")
   .GroupBy(x => x.LastError.PadRight(30, ' ').Substring(0, 30)).ToArray();

(Assuming this is LINQ to objects as SQL's SUBSTRING wouldn't throw an exception).