Compose LINQ-to-SQL predicates into a single predicate

Question

(An earlier question, Recursively (?) compose LINQ predicates into a single predicate, is similar to this but I actually asked the wrong question... the solution there satisfied

Answer 1

You can use the PredicateBuilder class

IQueryable SearchCustomers (params string[] keywords)
{
  var predicate = PredicateBuilder.False();

  foreach (string keyword in keywords)
  {
    // Note that you *must* declare a variable inside the loop
    // otherwise all your lambdas end up referencing whatever
    // the value of "keyword" is when they're finally executed.
    string temp = keyword;
    predicate = predicate.Or (p => p.Forenames.Contains (temp));
  }
  return dataContext.Customers.Where (predicate);
}

(that's actually the example from the PredicateBuilder page, I just adapted it to your case...)

---

EDIT:

Actually I misread your question, and my example above only covers a part of the solution... The following method should do what you want :

IQueryable SearchCustomers (string[] forenameKeyWords, string[] surnameKeywords)
{
    var predicate = PredicateBuilder.True();

    var forenamePredicate = PredicateBuilder.False();
    foreach (string keyword in forenameKeyWords)
    {
      string temp = keyword;
      forenamePredicate = forenamePredicate.Or (p => p.Forenames.Contains (temp));
    }
    predicate = PredicateBuilder.And(forenamePredicate);

    var surnamePredicate = PredicateBuilder.False();
    foreach (string keyword in surnameKeyWords)
    {
      string temp = keyword;
      surnamePredicate = surnamePredicate.Or (p => p.Surnames.Contains (temp));
    }
    predicate = PredicateBuilder.And(surnamePredicate);

    return dataContext.Customers.Where(predicate);
}

You can use it like that:

var query = SearchCustomers(
    new[] { "keyword1", "keyword2" },
    new[] { "keyword3", "keyword4" });

foreach (var Customer in query)
{
    ...
}