Using LINQ to get column value from column name when you have the row?

Question

I'm trying to convert some code that uses datasets to LINQ. Some of the code passes column names into other functions as strings.

Is there anyway I can easily rewrite this into LINQ?

string s = getElement(tr, elementName);

private string getElement (tableRow re, string elementName){
    if(tr[elementName] != null){
       return tr[elementName].toString()
    }
}

OR:

private void copy (tableRow trFrom, tableRow trTo){
   foreach (DataColumn c in trFrom.Table.Columns) {
        trTo[c.ColumnName] = trFrom[c.ColumnName];
   }
}

Answer to GVS: The reason to convert to LINQ is because it in many situations are easier to code LINQ and get better performance. It's related to another question here on stackoverflow: programming pattern using typed datasets

The reason I need to use the column name as a string is mainly because the column names are passed as a ID for input fields, they are then sent back to the program using AJAX (jquery).

Answer 1

Why would you convert working and clear code into something using LINQ?

Edit: LINQ is nice, cool stuff. But don't make the same errors as many XML fans did (specially first-adapters), by applying it to everything.

Answer 2

1. Simple way

   1.1. Using IEnumerable (Linq to Objects or similar) Change the elementName parameter for a Func and pass lambdas instead (you will get compile time checking as well!)

   1.2. Using IQueryable (Linq to SQL or similar) Same, but use Expression> instead.

2. Complex way: If for some reason you need to keep the parameter as an string (maybe is introduced by user) You can use reflection to build an expression tree at runtime http://msdn.microsoft.com/en-us/library/system.linq.expressions.expression.aspx.

   2.1. Using IEnumerable Then Compile, and use it as a parameter in a where, select...

   2.2. Using IQueryable Use it as a parameter in the where, select,

If you need to compose the lambda with other lambdas use this cool technique http://tomasp.net/blog/linq-expand.aspx

Answer 3

The answer is to use reflection.

Getting a value

private string getElement (tableRow tr, string element){
    string val = "";
    try
    {
        val = tr.GetType().GetProperty(element).GetValue(tr, null).ToString();
    }
    catch //NULL value
    {
        val = "";
    }
}

Or the copy scenario:

foreach (PropertyInfo c in tr.GetType().GetProperties())
{
    thr.GetType().GetProperty(c.Name).SetValue(thr,
         tr.GetType().GetProperty(c.Name).GetValue(tr, null), null);
}