How do I check for null or empty string for many arguments? - C#

What I can suggest is this:

private string _nullChecker(string _value){
   if (string.IsNullOrWhiteSpace(_value))
            throw new ArgumentException(_value + "Cannot be null or be   empty");
   return _value;
}

then, in your Where string statement

_Where = " WHERE " + _nullChecker(field) + " " + __nullChecker(operat) + " @" + _nullChecker(field) + "1 " + _nullChecker(andOr) + " " + _nullChecker(field2) + " " + _nullChecker(operat2) + " @" + _nullChecker(field2) + "2 ";

Not sure with this though. Haven't checked it with actual code. :) Hope this helps

You could do this:

int? GetLength(string s) {
    return s == "" ? -1 : s?.Length;
}

// s1, s2 and so on are your parameters
int? lengthSum = GetLength(s1) + GetLength(s2); // and so on
int wholeLength = (s1 + s2).Length; // and so on
if(lengthSum == wholeLength) {
    // No parameter is null or empty
}

Firstly, you can use simple libraries to do argument validation. Check out this one called Argument Validator, which has handy functions that will reduce your overall code by half.

Here is an example on how you could do it using the argument validator library:

public DB Where(string field, string operat, string value, string andOr, string field2, string operat2, string value2)
{
    var inputs = new string[] {field, operat, value, andOr, field2, operat2, value2};
    foreach(var input in inputs)
    {
        Throw.IfNullOrEmpty(input, nameof(input)));
    }
}    

I think I found a "branch" of what your are doing. There is less code below to check and the error is thrown within the function.

There is a great article of Adam Storr about arguments' checking here

For the lazy one you will find a use of extension methods, permitting to check argument in one line inside a try/catch.

It allows to check independently all arguments, and give a customed feedback

public returnType MyFunction(string arg1, string arg2, int arg3)
{
    try
    {
        // Check that the arguments are not null or empty
        _ = arg1.Valid() ?? throw new ArgumentNullException("Argument 1 not valid");
        _ = arg2.Valid() ?? throw new ArgumentNullException("The argument 2 must be provided");
        _ = arg3.Valid() ?? throw new ArgumentNullException("I need arg3 to work");
    }
    catch(ArgumentNullException)
    {
    //Treat the error
    }

And the implementation of the .Valid() method takes place in another files place wherever you want (stored in a TypeExtension file in this case) :

 public static class TypeExtensions
    {
        /// <summary>
        /// String method extension that return null if the string is null or empty.<br/>
        /// Otherwise return the value itself
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static object Valid(this string value)
        {
            return (!string.IsNullOrWhiteSpace(value)) ? value : null;
        }

        /// <summary>
        /// int method extension that return null if the int is null or 0 <br/>
        /// Otherwise return the value itself
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static object Valid(this int? value)
        {
            if (value is null or 0)
                return null;
            else
                return value;
        }
    }

So the argument inherit of the method Valid() by its type. The "null-coalescing operator" (??) means "if the value is null give what is next" The discard "_" means that no matter what is return it won't be stored in the memory.

So with the association of both you can check the argument, and if the check return null, throw an exception.

It is for the twisted mind I agree, but I didn't find a "cleaner" way so far. Maybe with decorator ?

I hope it might help !