Tag: Skip

Paging and the Entity Framework, Skip, and Take Part 3

Get the total count of pages. | Get the real page number. | Using Skip and Take to Page | The Actual Paging Controls

Ok so the last two posts have been arguably useless, maybe more so than anything else here, but they were somewhat needed because now I am going to show how to Linq, the Entity Framework, and well that’s it I think.

public static IList<ToolItem> GetSomeTools(String name, Int32 numberToShow, Int32 pageNumber, out Int32 realPage, out Int32 totalCountOfPages)
{
  //EntityContext.Context is just a singletonish version of the
  //Entities class.  Most people would use
  //  using (ToolEntities context = new ToolEnties())
  Int32 totalCount = EntityContext.Context.ToolItems
		   .Count(item => item.Name == name);
  //This is the method from the first post of this series
  //Just getting the count of pages based on numberToShow and
  //item totalCount
  totalCountOfPages = TotalCountOfPages(totalCount, numberToShow);
  //This is the method from the second post of this series
  //Basically getting the best possible page if the page number
  //is higher than the totalCountOfPages or lower than 0
  realPage = GetRealPage(totalCountOfPages, pageNumber);

  returnValue = EntityContext.Context.ChatRooms
			  .Where(item => item.Name == name )
			  .OrderBy(item => item.Name)
			  .Skip(numberToShow * realPage)
			  .Take(numberToShow)
			  .ToList();

  return returnValue.ToList();
}

Really simple yes? It follows like this:

Say I’m on page 1, which for this would be zero or pageNumber – 1. So I want to grab the first 20 items from the database. Well that means I want to start at 0 and grab 20. Now if you want this all to be done with some kind of conditional thing that either handles the first page or the other pages, you actually want to skip the same way no matter what the page number is. This is taken care of by numberToShow * realPage since even at 0 this works. After all 0 * anything is 0 and therefore you will be Skipping 0 items. So in other words, you’re at the start. Next you want to Take the amount of items you need, which is 20. Next time around you’ll start at 20 Skip(numberToShow 20 * realPage 1) and take the next 20. Nice thing is, even if you say Take 20 and there are only 2 left, it doesn’t care. It will just grab those two.

And there you have it, how to page with the Entity Framework and minimal amount of work. I know I hate taking other people’s methods (Like the TotalCountOfPages and GetRealPage methods), don’t know why. So sorry if I am forcing you to do so. However, the two methods I gave are semi important to this.

You might wonder why realPage and totalCountOfPages, well this is useful stuff when knowing what page is next for paging controls. Next post I’ll show those off but I’ll warn you, they are nothing spectacular.

Use Linq to Split a List: Skip and Take

Say what? Ok this is simple, and probably useless for most people but I thought I’d post it anyhow. Basically, say you have a huge list of something and you need to split it into smaller lists of something. This might be the case if you want to use parameterized SQL or something like HQL to send in a list full of somethings. Problem? Sql Server will only allow so many parameters to be sent in. Now you could send in a string in some cases, but meh. Kind of sloppy. So what do you do? You come here and you gank this method.

        public static IList<IList<T>> SplitList<T>
          (IList<T> listToSplit, Int32 countToTake)
        {
            IList<IList<T>> splitList = new List<IList<T>>();
            Int32 countToSkip = 0;

            do
            {
                splitList.Add(listToSplit.Skip(countToSkip)
                 .Take(countToTake).ToList());
                countToSkip += countToTake;
            } while (countToSkip < listToSplit.Count);

            return splitList;
        }

Pretty simple. It takes in a list of whatever and gives you back a list of lists of whatever. The fun part is using Skip and Take. Two methods I have come to love.

Basically you start out skipping nothing and taking a set amount… say 2000. Next time through, you start by skipping 2000 and taking the next 2000. Beauty of Take is it won’t just die on you if you don’t have enough items. It’ll just grab what’s left. Yay for take.