Question

I want to query my item in table Items, where the last update of each item must be less than 91 days old (from last update till now) and the quantity > 0.
This is my code in the Model:

public IList<Item> GetAllProducts()
{
 var ien_item = from i in this.DataContext.Items  
 orderby i.LastUpdated descending
 select i;
 return ien_item.ToList().Where(
                 s =>
                 HelperClasses.HelperClass.IsLastUpdate(s.LastUpdated.Value) == true 
                 && 
                 (s => s.Quantity) > 0
                 )
                 .ToList();

}

Anyone can solve it? Thanks.

Answer 1

We don’t really know what’s not working here. EDIT: Merlyn spotted it; your lambda syntax is messed up. There’s more to do here though.

However, I’d have thought you’d want this:

public IList<Item> GetAllProducts()
{
     var lastUpdateLimit = DateTime.UtcNow.Date.AddDays(-91);
     var query = from item in DataContext.Items
                 where item.Quantity > 0 && item.LastUpdated >= lastUpdateLimit
                 orderby item.LastUpdated descending
                 select item;
     return query.ToList();
}

Note that this is able to do all the querying at the database side instead of fetching all the items and filtering at the client side. It does assume that HelperClasses.HelperClass.IsLastUpdate is simple though, and basically equivalent to the filter I’ve got above.

(One additional point to note is that by evaluating UtcNow.Date once, the result will be consistent for all items – whereas if your code evaluates “today” on every call to IsLastUpdate, some values in the query may end up being filtered against a different date to other values, due to time progressing while the query is evaluating.)

EDIT: If you really need to use HelperClasses.HelperClass.IsLastUpdate then I’d suggest:

public IList<Item> GetAllProducts()
{
     var query = from item in DataContext.Items
                 where item.Quantity > 0
                 orderby item.LastUpdated descending
                 select item;
     return query.AsEnumerable()
                 .Where(s => HelperClass.IsLastUpdate(s.LastUpdated.Value))
                 .ToList();
}

… then at least the quantity filter is performed at the database side, and you’re not creating a complete buffered list before you need to (note the single call to ToList).