var Person = context.Persons.FirstOrDefault(search.GetExpression());

and there is nothing wrong with this as SearchCriteria is Message if I do this in a way u call service oriented I will have to create operationcontracts for each of parameters I could get as a filter criteria on client-side and I will end with tones of methods

GetPersonByName
GetPersonByBirthDate
GetPersonByIdCardNumber

and there are more than 60 entities and 1/3 of them will be search enabled. so pleas before u post your replay first carefully read question and after that give your remarks. I am not asking weather this is good or bad way all I am asking about is how to implement and if one says never do this first let me know how would u do this and after that I will think of better way.

@blowdart:

Messages not classes DataContract and DataMember this is how message is defined and we both know this as I wrote this is pseudo code so I just want to illustrate idea. if u mean custom messages with message headers  this is another story and not related to my question

public class PersonSearchCriteria
{
     public string FirstName {get; set;}
     public string LastName {get; set;}
     public int IdCardNumber {get; set;}
     
     Expression<Func<TSource, bool>> predicate
}

this is some pseudo code so I want to be able to create instance of this class and based on this properties values' filter my database in my databasecontext (which in this case is EntityFramework 4.0 with selft tracking entities.