Extending Entity Framework Queries To Facilitate Custom Paging

here are some applications where we need to display large sets of data. In order to display this large sets of data we usually follow the approach of Data paging. In asp.net there are data bound controls like Gridview, listview etc that can facilitate paging. The problem with this databound controls is that they perform paging on complete datasets. The asp.net databound controls brings the complete datasets and then perform paging at the application server side. This can led to network overload and server memory consuming every time user requests new data page.
Paging done at the database level is the best technique to optimize performance. In order to achieve this we have to build the appropriate query that will return only the required page result items.
In Entity Framework , we can do this by implementing an IQueryable<T> (http://msdn.microsoft.com/en-us/library/bb351562.aspx ) interface and building the required EF queries to get the paged result items from the database.

The following is an implementation of a simple extension method to offer paging functionality to simple Enitity framework or Linq to Sql query providers.

/// <summary>  
      /// Pages the specified query
      /// </summary>  
      /// <typeparam name="T">Generic Type Object</typeparam> 
       /// <typeparam name="TResult">The type of the result.</typeparam> 
       /// <param name="query">The Object query where paging needs to be applied.</param> 
       /// <param name="pageNum">The page number.</param> 
       /// <param name="pageSize">Size of the page.</param> 
       /// <param name="orderByProperty">The order by property.</param>   
     /// <param name="isAscendingOrder">if set to <c>true</c> [is ascending order].</param>  
      /// <param name="rowsCount">The total rows count.</param>   
     /// <returns></returns>      

  private static IQueryable<T> PagedResult<T, TResult>(IQueryable<T> query, int pageNum, int pageSize,                         Expression<Func<T, TResult>> orderByProperty, bool isAscendingOrder, out int rowsCount)         {     
       if (pageSize <= 0) pageSize = 20;            
           //Total result count  
          rowsCount = query.Count();  
                     //If page number should be > 0 else set to first page     
       if (rowsCount <= pageSize || pageNum <= 0) pageNum = 1; 
                      //Calculate number of rows to skip on pagesize
           int excludedRows = (pageNum - 1) * pageSize;
           query = isAscendingOrder ? query.OrderBy(orderByProperty) : query.OrderByDescending(orderByProperty);  
                     //Skip the required rows for the current page and take the next records of pagesize count  

          return query.Skip(excludedRows).Take(pageSize); 
       }

xample to use:
Lets assume a simple query that returns some articles from an Articles table. We will call this method to get the first 20 items for the first page.

var articles = (from article in Articles 
                where article.Author == "Abc" 
                select article); 
int totalArticles;  
  var firstPageData = PagedResult(articles, 1, 20, article => article.PublishedDate, false, out totalArticles);
or simply for any entity
var context = new AtricleEntityModel(); var query = context.ArticlesPagedResult(articles, <pageNumber>, 20, article => article.PublishedDate, false, out totalArticles);

Accordingly this method can be invoked by passing the page number for other pages.

Maninder Singh Puhi , Sr Developer, Mindfire Solutions.

Related Tags: Entity Framework, LINQ using C sharp, Paging

Author : Maninder Singh Puhi

Extending Entity Framework Queries To Facilitate Custom Paging

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