Dynamic LINQ

Question

I have an XML document defined like so

XML File

<TABLE>
    <RECORD>
     <PAGENUMBER> 1 Of 1</PAGENUMBER>
     <OtherFields1>..</OtherFields1>
     <OtherFields2>..</OtherFields2>
    </RECORD>
    <RECORD>
     <PAGENUMBER> 1 Of 2</PAGENUMBER>
     <OtherFields1>..</OtherFields1>
     <OtherFields2>..</OtherFields2>
    </RECORD>
    <RECORD>
     <PAGENUMBER> 2 Of 2</PAGENUMBER>
     <OtherFields1>..</OtherFields1>
     <OtherFields2>..</OtherFields2>
    </RECORD>
    <RECORD>
     <PAGENUMBER> 1 Of 1</PAGENUMBER>
     <OtherFields1>..</OtherFields1>
     <OtherFields2>..</OtherFields2>
    </RECORD>
</TABLE>

I'm trying to create a dynamic query where i can put a "Fieldname", "Operand", "Value" in a config and LINQ can build a predicate based on it.

Config File

<CLAUSES>
    <CLAUSE name="PAGENUMBER" operand="!=">Page 1 Of 1</CLAUSE>
    <CLAUSE name="OtherFields1" operand="!=">String.Empty</CLAUSE>
</CLAUSES>

Here is the LINQ i'm using now

LINQ Query

        XDocument jobXML = XDocument.Load(JobFile);

        List<ClauseObj> clauses = new List<ClauseObj>();
        clauses.Add(new ClauseObj { Field = "PAGENUMBER", Operand = "!=", Value = " Page 1 Of 1" });

        var q = jobXML.Descendants("RECORD").AsEnumerable();

        foreach (var c in clauses)
        {
            switch (c.Operand)
            {
                case "!=":
                    q = q.Where(r => r.Element(c.Field).Value != c.Value);
                    break;
            }
        }

how can i make it read the where clauses "dynamically" and also specify which field names to return?

Answer 1

Have a look at the Dynamic Linq Queries Sample. They have a class in there that adds various extensions methods for Where and Order By

Answer 2

string clause = "PAGENUMBER";
string operand = "!=";
string value= " Page 1 Of 1";

  var q = from r in jobXML.Descendants("RECORD")
                 select new
                 {
                     PAGENUMBER = (string)r.Element("PAGENUMBER"),
                     OtherFields1 = (string)r.Element("OtherFields1")
                 }

   switch(operand)
   {
       case "!=":
          q = q.Where(r=> r.Element(clause).Value != value);
          break;
       case "etc":
   }

   var list = q.ToList();