Dynamic LINQ OR Conditions - linq

Question

I'm looking to use LINQ to do multiple where conditions on a collection similar to
IEnumerable<Object> items;
items.Where(p => p.FirstName = "John");
items.Where(p => p.LastName = "Smith");
except for rather than having multiple AND conditions (as with this example), I'd like to have multiple OR conditions.
EDIT
Sorry, to clarify I don't know how many of these conditions I will have so
items.Where(p => p.FirstName = "John" || p => p.LastName = "Smith")
won't work.
Basically, here's what I'm trying to do:
foreach(var name in names)
{
items = items.Where(p => p.Name == name);
}

Answer 1

Use PredicateBuilder:
Suppose you want to write a LINQ to SQL or Entity Framework query that implements a keyword-style search. In other words, a query that returns rows whose description contains some or all of a given set of keywords...
The ideal approach is to dynamically construct a lambda expression tree that performs an or-based predicate.
Of all the things that will drive you to manually constructing expression trees, the need for dynamic predicates is the most common in a typical business application. Fortunately, it’s possible to write a set of simple and reusable extension methods that radically simplify this task. This is the role of our PredicateBuilder class...

Answer 2

It sounds like your whitelist of names is only known at runtime. Perhaps try this:
string[] names = new string[] {"John", "foo", "bar"};
var matching = items.Where(x => names.Contains(x.Name));

Answer 3

You can use .Union() to return results that satisfy any condition.
var results = items.Where(p => p.FirstName == "John")
.Union(items.Where(p => p.LastName == "Smith"));
This is inferior to using the || operator. It isn't clear from your edit why that wouldn't work.

Answer 4

public static Expression<Func<T, bool>> OrTheseFiltersTogether<T>(
this IEnumerable<Expression<Func<T, bool>>> filters)
{
Expression<Func<T, bool>> firstFilter = filters.FirstOrDefault();
if (firstFilter == null)
{
Expression<Func<T, bool>> alwaysTrue = x => true;
return alwaysTrue;
}
var body = firstFilter.Body;
var param = firstFilter.Parameters.ToArray();
foreach (var nextFilter in filters.Skip(1))
{
var nextBody = Expression.Invoke(nextFilter, param);
body = Expression.OrElse(body, nextBody);
}
Expression<Func<T, bool>> result = Expression.Lambda<Func<T, bool>>(body, param);
return result;
}
Then, later:
List<Expression<Func<Person, bool>>> filters = names
.Select<string, Expression<Func<Person, bool>>>(name =>
p => p.Name == name
).ToList();
Expression<Func<Person, bool>> filterOfOrs = filters.OrTheseFiltersTogether();
query = query.Where<Person>(filterOfOrs);

Answer 5

You can't make the Where clause dynamic, but you can dynamically create the Lambda Expression you pass to it. Create the right Expression, compile it and pass the resulting lambda expression as a parameter to the Where clause.
EDIT:
Okay, seems like you can skip the part where you have to manually create the Expression and can use PredicateBuilder for it, as already answered by AS-CII.