Select entities where ID in int array - WCF Data Services, LINQ

Question

I would like to return a set of entities who has and ID that is contained in a list or array of IDs using LINQ and Data Services. I know how to this using LinqToEF but I am

Answer 1

Here is my realization of WhereIn() Method, to filter IQueryable collection by a set of selected entities:

 public static IQueryable WhereIn(this IQueryable source, Expression> memberExpr, IEnumerable values) where T : class
    {
        Expression predicate = null;
        ParameterExpression param = Expression.Parameter(typeof(T), "t");

        bool IsFirst = true;

        // Create a comparison for each value eg:                 
        // IN:  t => t.Id == 1 | t.Id == 2                

        MemberExpression me = (MemberExpression) memberExpr.Body;
        foreach (TProp val in values)
        {
            ConstantExpression ce = Expression.Constant(val);


            Expression comparison = Expression.Equal(me, ce);

            if (IsFirst)
            {
                predicate = comparison;
                IsFirst = false;
            }
            else
            {
                predicate = Expression.Or(predicate, comparison);
            }
        }

        return predicate != null
            ? source.Where(Expression.Lambda>(predicate, param)).AsQueryable()
            : source;
    }

And calling of this method looks like:

IQueryable q = context.Products.ToList();

var SelectedProducts = new List
{
  new Product{Id=23},
  new Product{Id=56}
};
...
// Collecting set of product id's    
var selectedProductsIds = SelectedProducts.Select(p => p.Id).ToList();

// Filtering products
q = q.WhereIn(c => c.Product.Id, selectedProductsIds);