How to create a dynamic LINQ query where clause

Question

How would I create a where clause with multiple ORs based off a List?

I know it won't work, but here's what I'm trying to achieve. I haven't found a suitable method for doing it yet. For every one of the strings passed in, I need to add an OR where clause. The list could contain multiple tag strings and I need the query to add an OR where clause for each of them.

public void GetItems(List<String> tagsToGet){
    var tagQuery = from tag in ParseObject.GetQuery("Tag")
                   foreach(string tagToGet in tagsToGet){
                            where tag.Get<string>("name") == tagToGet || // next loop
                   }
                   select tag;
}

Answer 1

You can go with method chain:

public void GetItems(List<String> tagsToGet){
    var tagQuery = ParseObject.GetQuery("Tag");

    foreach(string tagToGet in tagsToGet)
    {
            tabQuery = tabQuery.Where(w => w.Get<string>("name") == tagToGet).AsEnumerable(); || // next loop
    }

}

Answer 2

This should work:

where tagsToGet.Contains(tag.Get<string>("name"))

or possibly

where t=> tagsToGet.Any(ttg => String.Equals(ttg, t.Get<string>("name"), StringComparison.CurrentCultureIgnoreCase))

Obviously you can replace the comparison with any other way you prefer.

Another alternative, more linq-tastic:

var tagQuery = from tag in ParseObject.GetQuery("Tag")
               join tagToGet in tagsToGet
                 on tagToGet equals tag.Get<string>("name")
               select tag;

Answer 3

Have a look at PredicateBuilder . The second example should fit your requirements:

IQueryable<Product> SearchProducts (params string[] keywords)
{
  var predicate = PredicateBuilder.False<Product>();

  foreach (string keyword in keywords)
  {
    string temp = keyword;
    predicate = predicate.Or (p => p.Description.Contains (temp));
  }
  return dataContext.Products.Where (predicate);
}

If querying with Entity Framework, change the last line to this:

return objectContext.Products.AsExpandable().Where (predicate);

Answer 4

You want to use Dynamic LINQ. Get NuGet package System.Linq.Dynamic and see an example here: http://weblogs.asp.net/ricardoperes/dynamic-linq