Linq to Entities Skip() and Take()

Question

I am working on an ASP.NET application and I am creating a LINQ query which will select paginated records from db. on user interface I have a listbox where user can select multiple choices. I want to know:

How can I increment Skip(), Take() parameters to view next results ?
How can I use "IN" key word so that if user selects multiple options from listbox, query can check all values ?

My query looks like this:

var searchResults = context.data_vault.Where(d => d.STATE == lstStates.SelectedItem.Text).OrderBy(d= > d.dv_id).Take(10).Skip(2);    
GridView1.DataSource = searchResults;
GridView1.DataBind();

You need to first call skip and then take. In your current implementation you will always retrieve the items 3 to 10, because you take the first 10 and from those you skip the first two. To increment you only need to supply the value for skip as a parameter to your method where the query is executed. — Franky, Jun 08 '12 at 14:16

score 22 · Answer 1 · answered Jun 08 '12 at 14:13

I think you are using Skip incorrectly. It should be before the Take.

Skip skips a number of records, so for your first page, pass in 0, else pass in the (page number - 1) * records per page.

I usually do something like this:

int Page = 1;
int RecordsPerPage = 10;
var q = yourQuery.Skip((Page - 1) * RecordsPerPage).Take(RecordsPerPage);

abatishchev · Answer 2 · 2012-06-08T14:53:57.660

7

You need to turn paging on the GridView first. Then on PageIndexChanging event:

var result = db.Where(...)
               .Skip(e.NewPageIndex * grid.PageSize)
               .Take(grid.PageSize)
               .ToList(); // this is very important part too

To emulate IN behavior:

var selection = list.SelectedItems.Select(i => i.Text).ToArray();
var result = db.Where(x => selection.Contains(x.Prop));

edited Jun 08 '12 at 14:53

answered Jun 08 '12 at 14:09

abatishchev

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Add Closing brackets in second query. `db.Where(x => selection.Contains(x.Prop));` – Nikhil Agrawal Jun 08 '12 at 14:13
@abatishchev What I need to write on page load ? – DotnetSparrow Jun 08 '12 at 14:44
@DotnetSparrow: Bind the list onto the GridView. Then it will perform paging by itself. – abatishchev Jun 08 '12 at 14:44
but it will slow down things because on page load it will bring all records ? – DotnetSparrow Jun 08 '12 at 14:47
@DotnetSparrow: No, EF will limit query result. Of course it will be less efficient then manual limiting (that's a known issue of SQL Server). – abatishchev Jun 08 '12 at 14:50
Also, I see that var selection = list.SelectedItems.Select(i => i.Text).ToArray(); list.selectedItems doesn't exist. – DotnetSparrow Jun 08 '12 at 14:55
@DotnetSparrow: `list` means your `lstStates`. What is its type? I thought this is `System.Web.UI.WebControls.ListBox`. – abatishchev Jun 08 '12 at 14:56
yes it is listbox control but still not showing this selecteditems – DotnetSparrow Jun 08 '12 at 15:33
@DotnetSparrow: Indeed, only `SelectedItem`. How do you receive multiple selection from user? – abatishchev Jun 08 '12 at 16:19
@DotnetSparrow: Have I answered the original question? :) – abatishchev Jun 08 '12 at 17:21

score 1 · Answer 3 · answered Jun 08 '12 at 14:17

1

Try this:

   int temp = (CurrentPageNumber - 1) * 10;
    var searchResults = context.data_vault.Where(d => d.STATE == lstStates.SelectedItem.Text).OrderBy(d= > d.dv_id).Skip(temp).Take(10);

answered Jun 08 '12 at 14:17

Kapil Khandelwal

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Linq to Entities Skip() and Take()

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