Question

This may seem a little “much”, but this is picking at me!

Envision a form with a CheckBoxList that acts as an inclusive filter for a user.

This user fills out a form, checks off which items in the filter they want, and off they go.

I’m looking for a concise way to write the following LINQ statement:

If NO items are checked, show all results
else
Show results filtered by user selection

Is it possible (and if so, how) to write this without using a conditional statement that basically is the same query, but without the Contains method?

I tried putting a ternary operator in my Where clause, but the compiler didn’t like it at all.

System.Collections.Generic.List catIds = new System.Collections.Generic.List();

              foreach (ListItem lstItemCategory in lstCategories.Items)
              {
                  if (lstItemCategory.Selected)
                  {
                      catIds.Add(Convert.ToInt64(lstItemCategory.Value));
                  }
              }

              var qry = from rategroup in rategroups
                        from rate in rategroup.Rates
                        orderby rate.RateClass.Id descending
                        select new
                        {
                            Category = rate.Product.ProductCategories[0].Category.Description,
                            rate.Product.Description,
                            Carrier = rate.CarrierName,
                            Id = rate.Product.ProductCategories[0].Id
                        };


              this.gvSchedule.DataSource = qry.Where(x => catIds.Contains(x.Id)).OrderBy(x => x.Category).ThenBy(x => x.Carrier).ToArray();
              this.gvSchedule.DataBind();

Answer 1

Why not just do:

var filteredQry = catIds.Any() ? qry.Where(x => catIds.Contains(x.Id)) : qry;
this.gvSchedule.DataSource = filteredQry.OrderBy(x => x.Category)
                                        .ThenBy(x => x.Carrier)
                                        .ToArray();

Or:

if(catIds.Any())
    qry = qry.Where(x => catIds.Contains(x.Id));

this.gvSchedule.DataSource = qry.OrderBy(x => x.Category)
                                .ThenBy(x => x.Carrier)
                                .ToArray();

You could also try using an Expression<Func<Foo, bool>> filter and assigning it to an ‘always true’ predicate or the genuine filter depending on the condition, but this will be slightly difficult since an anonymous type is involved.