Query conditions with an OR, not the AND

We are trying to build a search tool and the searchable fields are going to vary. Is it possible to conditionally concatenate a queries where clause joining the conditions with an or operator rather than the and operator? This code is close but builds the condition using and. How can I build the query by joining the conditions with an or?

var results= from c in uow.Clients where c.Lastnmae.StartsWith = "al" select c;

if (!string.IsNullOrEmpty(searchCriteria.StreetAddress)) results = results.Where(c => c.StreetAddress.StartsWith(searchCriteria.StreetAddress));

if (!string.IsNullOrEmpty(searchCriteria.FirstName)) results = results.Where(c => p.Firstname.StartsWith(searchCriteria.FirstName));

Thanks

This is how I'm doing it:

Query query = new Query(typeof(Client));
query.QueryExpression = Entity.Attribute("LastName") == "ab";
if(x)
   query.QueryExpression |= Entity.Attribute("FirstName") == "ab";
if(y)
   query.QueryExpression |= Entity.Attribute("Company") == "def";

var entities = UnitOfWork.Find<Client>(query);

There are all sorts of expressions you can build up this matter, I'm not sure how to do this using LINQ.

Thanks for that:) I'll give it a try

Thanks for that:) I'll give it a try