Declaring an empty Queryable?

Question

How do I declare such a variable?

            var rData = from nc in ctx.NEWSLETTER_CLIENTS                         join ni in ctx.NEWSLETTER_INDICES on nc.INDEX_NUM                                                            equals ni.INDEX_NUM                         select new                         {                             ClientID = nc.CLIENT_ID,                             Email = nc.CLIENT_EMAIL_ADDRESS,                             Index = nc.INDEX_NUM,                             MainClass = ni.MAIN_CLASS,                             SubClass = ni.SUB_CLASS,                             App1 = ni.VALUE_1,                             App2 = ni.VALUE_2,                             App3 = ni.VALUE_3,                             App4 = ni.VALUE_4                         };          // Now I need to declare on a variable named fData under the function scope,         // so I can later use it:          var fData = ...; //What do I declare here?          if(x)             fData = fData.Concat(rData.Where(u => ...));         if(y)             fData = fData.Concat(rData.Where(u => ...));         // etc 

Answer 1

IQueryable<type of p> fData = null; 

If you want to use the query later (iow after the if):

var fData = Enumerable.Empty<type of p>().AsQueryable(); 

Update:

Now for using with anonymous types:

IQueryable<T> RestOfMethod<T>(IQueryable<T> rData) {   var fData = Enumerable.Empty<T>().AsQueryable(); // or = rData;    if(x)     fData = fData.Concat(rData.Where(u => ...));   if(y)     fData = fData.Concat(rData.Where(u => ...));    return fData; }  // original code location var rData = some query; var fData = RestOfMethod(rData); 

Update 2:

As pointed out, the above does not actually work, as the predicate of Where does not know the type. You could refactor it some more to include the predicates in the parameters, example:

IQueryable<T> RestOfMethod<T>(IQueryable<T> rData,    Expression<Func<T,bool>> pred1,   Expression<Func<T,bool>> pred2)  { ... } 

Update 3: (perhaps hacky)

var fData = rData.Take(0); // should be cheap.