How to make a compound "or" clause in Linq?

Question

If you're adding "and" conditions to a Linq query, it's easy to do it like so:

var q = MyTable;
if (condition1)
  q = q.Where(t => t.Field1 == value1);
if (condition2)
  q = q.Where(t => t.Field2 > t.Field3);
// etc.

Is there any clever way of doing the same thing, when you want to add "or" conditions?

Answer 1

You can use a PredicateBuilder and use it to build an Or based expression:

 var predicate = PredicateBuilder.False<Product>();

 predicate = predicate.Or (t => t.Field1 == value1);
 predicate = predicate.Or (t => t.Field2 > t.Field3);

 q = q.Where (predicate);

You can read more about it here: http://www.albahari.com/nutshell/predicatebuilder.aspx

Replace the Product in PredicateBuilder.False<Product>() with your queried object.

Note that you start from a False predicate as you want to use Or. If You'd want an And predicate, Yuo should start from a True

Answer 2

Use the following:

var q = MyTable;
q = q.Where(
     t => (condition1 && t.Field1 == value1) || (condition2 && t.Field2 > t.Field3));