Paging in Entity Framework - entity-framework

Question

In Entity Framework, using LINQ to Entities, database paging is usually done in following manner:
int totalRecords = EntityContext.Context.UserSet.Count;
var list = EntityContext.Context.UserSet
.Skip(startingRecordNumber)
.Take(pageSize)
.ToList();
This results in TWO database calls.
Please tell, how to reduce it to ONE database call.
Thank You.

Answer 1

Whats wrong with two calls? They are small and quick queries. Databases are designed to support lots of small queries.
A developing a complex solution to do one query for paging isn't going give you much pay off.

Answer 2

Using Esql and mapping a stored procedure to an entity can solve the problem.
SP will return totalRows as output parameter and current page as resultset.
CREATE PROCEDURE getPagedList(
#PageNumber int,
#PageSize int,
#totalRecordCount int OUTPUT
AS
//Return paged records
Please advise.
Thank You.

Answer 3

Hmmm... the actual call that uses paging is the second one - that's a single call.
The second call is to determine the total number of rows - that's quite a different operation, and I am not aware of any way you could combine those two distinct operations into a single database call with the Entity Framework.
Question is: do you really need the total number of rows? What for? Is that worth a second database call or not?
Another option you would have is to use the EntityObjectSource (in ASP.NET) and then bind this to e.g. a GridView, and enable AllowPaging and AllowSorting etc. on the GridView, and let the ASP.NET runtime handle all the nitty-gritty work of retrieving the appropriate data page and displaying it.
Marc

Answer 4

ALTER proc [dbo].[GetNames]
#lastRow bigint,
#pageSize bigint,
#totalRowCount bigint output
as
begin
select #totalRowCount = count(*) from _firstNames, _lastNames
select
FirstName,
LastName,
RowNumber
from
(
select
fn.[FirstName] as FirstName,
ln.[Name] as LastName,
row_number() over( order by FirstName ) as RowNumber
from
_firstNames fn, _lastNames ln
) as data
where
RowNumber between ( #lastRow + 1 ) and ( #lastRow + #pageSize )
end
There is no way to get this into one call, but this works fast enough.

Answer 5

This queries are too small for DBManager and I can not understand why you want to do this, anyway for reduce it to ONE database call use this:
var list = EntityContext.Context.UserSet
.Skip(startingRecordNumber)
.Take(pageSize)
.ToList();
int totalRecords = list.Count;

Answer 6

Suppose you want to get the details of Page 2 with a pagesize=4
int page =2;
int pagesize=4;
var pagedDetails= Categories.Skip(pagesize*(page-1)).Take(pagesize)
.Join(Categories.Select(item=>new {item.CategoryID,Total = Categories.Count()}),x=>x.CategoryID,y=>y.CategoryID,(x,y)=>new {Category = x,TotalRows=y.Total});
The Output will have all details of Category and TotalRows.
One DB call.
Generated SQL
-- Region Parameters
DECLARE #p0 Int = 2
DECLARE #p1 Int = 4
-- EndRegion
SELECT [t2].[CategoryID], [t2].[CategoryName], [t2].[Description], [t2].[Picture], [t5].[value] AS [TotalRows]
FROM (
SELECT [t1].[CategoryID], [t1].[CategoryName], [t1].[Description], [t1].[Picture], [t1].[ROW_NUMBER]
FROM (
SELECT ROW_NUMBER() OVER (ORDER BY [t0].[CategoryID], [t0].[CategoryName]) AS [ROW_NUMBER], [t0].[CategoryID], [t0].[CategoryName], [t0].[Description], [t0].[Picture]
FROM [Categories] AS [t0]
) AS [t1]
WHERE [t1].[ROW_NUMBER] BETWEEN #p0 + 1 AND #p0 + #p1
) AS [t2]
INNER JOIN (
SELECT [t3].[CategoryID], (
SELECT COUNT(*)
FROM [Categories] AS [t4]
) AS [value]
FROM [Categories] AS [t3]
) AS [t5] ON [t2].[CategoryID] = [t5].[CategoryID]
ORDER BY [t2].[ROW_NUMBER]