Need help in resolving error in predicates for And operator in LINQ

Question

Hi,

I got into problem of predicate And operator. Code is :

SQLDBDataContext sqlDS = new SQLDBDataContext();
Expression<Func<User,bool>> pred = null; //delcare the predicate to start with.

if (Request["Name"] != null && ! Request["Name"].Equals(string.Empty))
{  
   pred = c => ( c.ContactFirst.Contains(Request["Name"]) || c.ContactLast.Contains(Request["Name"]));
}

if (Request["Company"] != null && !Request["Company"].Equals(string.Empty))
{
   if (pred == null) { 
      pred = (c => c.Company.Contains(Request["Company"])); 
   }
   else {
      pred = pred.And(c => c.Company.Contains(Request["Company"]));
   }
}

error is line : [ else {pred = pred.And(c => ] No overload for method 'And' takes '1' arguments

Can anybody tell me how to use .And operator to predicate.

Thanks in advance.
Anil

Answer 1

And is the binary And operator; you mean Expression.AndAlso, i.e.

pred = Expression.AndAlso(pred, {new bit})

However, I suspect you are doing this the hard way. It is easier to use things like:

IQueryable<Foo> source = ...
if(condition1) {
    source = source.Where(predicate1);
}
if(condition2) {
    source = source.Where(predicate2);
}

For example:

IQueryable<User> source = ...
string name = Request["Name"];
if(!string.IsNullOrEmpty(name)) {
    source = source.Where(user => user.ContactFirst.Contains(name)
               || user.ContactLast.Contains(name));
}
string company = Request["Company"];
if(!string.IsNullOrEmpty(company)) {
    source = source.Where(user => user.Company.Contains(company));
}

Answer 2

A nifty little library to have is the Predicate Builder from the C# 3.0 in a Nutshell guys - http://www.albahari.com/nutshell/predicatebuilder.aspx