Question

Quick question about using IQueryable objects. Can I do something like that and if not – what is the alternative way?

IQueryable<Item> q = this.ObjectContext.items;

q = q.Where(i => i.price > 100);

...

q = q.Where(i => i.class_name.Contain("apple"));

Update: Here is full code of my function (may be I’m missing something):

public IQueryable<item> Getitem(string filter)
{
    // filtering by user departments
    IQueryable<item> pre_q = from t_item in this.ObjectContext.items
        join t_useritems in this.ObjectContext.user_to_item on
        t_item.number equals t_useritems.number
        where t_useritems.user_name == this.userName
        select t_item;

    if (filter != null)
    {
        QueryFilter qf = new QueryFilter(filter);
        string _excludeClass = qf.GetPropertyValueByName("excludeClass");
        string _excludeSubcat = qf.GetPropertyValueByName("excludeSubcat");
        string _searchBy = qf.GetPropertyValueByName("searchby");
        string _search = qf.GetPropertyValueByName("search");

        if (!string.IsNullOrEmpty(_excludeClass))
            pre_q = pre_q.Where(i => i.class_name != _excludeClass);

        if (!string.IsNullOrEmpty(_excludeSubcat))
            pre_q = pre_q.Where(i => i.subcat_name != _excludeSubcat);

        if (!string.IsNullOrEmpty(_searchBy) && !string.IsNullOrEmpty(_search))
        {
            if (_searchBy == "number")
                pre_q = pre_q.Where(i => i.number.Contains(_search));
            else if (_searchBy == "description")
                pre_q = pre_q.Where(i => i.description.Contains(_search));
            else if (_searchBy == "class_name")
                pre_q = pre_q.Where(i => i.class_name.Contains(_search));
            else if (_searchBy == "cat_name")
                pre_q = pre_q.Where(i => i.cat_name.Contains(_search));
            else if (_searchBy == "subcat_name")
                pre_q = pre_q.Where(i => i.subcat_name.Contains(_search));
            else if (_searchBy == "all_fields")
                pre_q = pre_q.Where(i => i.number.Contains(_search) ||
                  i.description.Contains(_search) ||
                  i.class_name.Contains(_search) ||
                  i.cat_name.Contains(_search) ||
                  i.subcat_name.Contains(_search));
            }
        }
    }
    return pre_q.OrderBy(i => i.number);
}

Essentially what’s happening – I pass excludeClass filter and some search text filter. After applying excludeClass I can see that number of records is correct, however when I after apply search filter – it basically reset already filtered items and they are getting back in the result.

Answer 1

Yes, you can. IQueryable<T> is “composable”. That’s fine. It will only evaluate the final composed query when you do something that needs the data, for example a ToList(), a foreach, or an aggregate such as Count(), Max(), etc. That pattern is pretty much how a lot of multi-field search screens work.