Question

I am trying to do an OR. I thought you could do this with Predicate, so I tried this

var products = ctx.Products.Where(x => .....);

var predicate = PredicateBuilder.False<Product>();
foreach (Category categ in categs)
  predicate = predicate.Or(p => p.Categories.Select(c => c.Id).Contains(categ.Id)
                              || p.Categories.Select(c => c.Category1.Id).Contains(categ.Id)
                              || p.Categories.Select(c => c.Category1.Category1.Id).Contains(categ.Id));
products = products.Where(predicate);

but it gives me this error

System.NotSupportedException: The LINQ expression node type ‘Invoke’ is not supported in LINQ to Entities.

Could someone please help me solve this? Thanks in advanced.

A Product can have one or more Category.
Category may have a “parent category” called Category1. Those long 3 lines above is to select products under a category or its child categories.

I googled and found LinqKit, but I want to avoid adding a 3rd party just for this. But if I have to use LinqKit, is it easy to install?

Answer 1

I think this works

if (categs.Length > 0)
{
  List<Product> tmpProducts = new List<Product>();
  foreach (Category c in categs)
  {
    var tmp = ctx.Products.ToList().Where(x => x.IsUnderCategory(c));
    tmpProducts = tmpProducts.Union(tmp).ToList();
  }
  products = products.ToList().Intersect(tmpProducts).AsQueryable();
}

IsUnderCategory is an extension

  public partial class Category
  {
    public bool IsUnderCategory(Category categ)
    {
      if (Id == categ.Id) return true; // is itself

      if (Parent == null)
        return false;

      return Parent.IsUnderCategory(categ);
    }
  }