Record navigation with Paging

  • Thread starter Thread starter Hari
  • Start date Start date
H

Hari

Hi,

Iam working with a custom grid control to navigate
navigate large number of records from a table.
The control need to have row up, row down, page up, page
down features.

Requirements are :
page size = 30 records
maximum records in database table - 20,000 (each record
150K)

I was looking the msdn sample:(Paging through a query
result) its shows building dynamic query for every pages.
So inorder to this way, if i want to navigate a singe row
( up/down (one record) do i need to build a query every
time? or is there any better way to approach this??

please help me guys......

Hari

The sample i was looking :
case "Next":
selCmd.CommandText = "SELECT TOP " + pageSize + "
CustomerID, CompanyName FROM Customers " +
"WHERE CustomerID > @CustomerId
ORDER BY CustomerID";
selCmd.Parameters.Add("@CustomerId",
SqlDbType.VarChar, 5).Value = lastVisibleCustomer;
break;
case "Previous":
selCmd.CommandText = "SELECT TOP " + pageSize + "
CustomerID, CompanyName FROM Customers " +
"WHERE CustomerID < @CustomerId
ORDER BY CustomerID DESC";
selCmd.Parameters.Add("@CustomerId",
SqlDbType.VarChar, 5).Value = firstVisibleCustomer;
break;
default:
selCmd.CommandText = "SELECT TOP " + pageSize + "
CustomerID, CompanyName FROM Customers ORDER BY
CustomerID";

// Determine total pages.
SqlCommand totCMD = new SqlCommand("SELECT Count
(*) FROM Customers", nwindConn);
nwindConn.Open();
int totalRecords = (int)totCMD.ExecuteScalar();
nwindConn.Close();
totalPages = (int)Math.Ceiling((double)
totalRecords / pageSize);

break;
 
I'd use a DataTable, build a dataview on it, store it in session state, and
then just set the RowFilter property
http://www.knowdotnet.com/articles/advancedrowfilter.html to filter the
data. 20,000 rows is a buttload of data and it's doubtful that you need that
much data at one time - if you can use 5,000 and cache it, then if they
select something in the next 5,000 hit the db again, and the same for the
next 5,000 but assuming you do, you don't want to make unnecessary trips
back to the db each time. If the user erroneously clicks forward then
backward, you don't want to make two trips to the db on an accident. A
DataView is probably the more efficient way to go in this scenario but as
with anything, the devil will be in the details.
 
Some Paging tips that work for any database (so don't need stored procedures
or TOP directive):

1) Build a middle tier that takes the sql request (select and page number)
2) Middle tier queries the database and save the results as XML
3) Middle tier sends back part of the XML according to page number. Also
sends name of saved file.
4) Client side receives page and filename.
5) Client displays page and asynchronously requests next page while user
browses current.
6) Middle tier receives request for next page with filename and sends it
back.

By putting middle tier and database on seperate machines you spread the cpu
load.
By async selecting next page the user is unaware of paging times.

Another thing to watch out for is the ORDER BY clause, the above works for
any order of the rows.

ian.
 
Thanks for your responce.

This solution seems to work with single page data at a
time, but iam looking mainly with single record(mostly
mapped to a row)navigation.. any more thoughts??

Hari
 
Thanks for the info Ryan,

The main thing is i don't want to keep more than 5 pages
of data (5*30) in the memory. Also the main focus is user
should be able to navigate with single record, in addtion
to a page navigation.
Also in my application the UI is build with unmanaged MFC
app and only the storage access layer is in the mananged
DDLL with ADO.NET. So i would like to build the custom
DataView to accomodate these requirement.

Also the Table need to maintain a fixed number of records.
(only last n(20,000) rows should be remain in the table).

Any more thoughts??

-Hari
 
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