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LINQ and Dynamic Predicate Construction at Runtime

, 13 Aug 2008
Illustrating a multi-predicate injection pattern now possible with the new features of C# 3.0.
LINQDynamicPredicate_demo.zip
LINQDynamicSearchDemo
App_Data
Global.asax
NorthwindDB.dbml
NorthwindDB.dbml.layout
Properties
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.SessionState;
using System.Data.SqlClient;

namespace LINQDynamicSearchDemo {
    public class Global : System.Web.HttpApplication {

        protected void Application_Start(object sender, EventArgs e) {
          /*  using (SqlConnection conn = new SqlConnection(@"Data Source=.\SQLExpress;Database=master;Integrated Security=True;")) {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand()) {
                    cmd.CommandType = System.Data.CommandType.StoredProcedure;
                    cmd.CommandText = "sp_attach_single_file_db";

                    cmd.Parameters.AddWithValue("@dbname", "Northwind");
                    cmd.Parameters.AddWithValue("@physname", Server.MapPath("~/App_Data/NORTHWND.MDF"));
                    cmd.ExecuteNonQuery();
                }
            }*/
        }

        protected void Session_Start(object sender, EventArgs e) {

        }

        /// <summary>
        /// starting the request, build a context and stash it
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Application_BeginRequest(object sender, EventArgs e) {
            NorthwindDBDataContext ctx = new NorthwindDBDataContext();
            HttpContext.Current.Items["RequestContext"] = ctx;

        }

        /// <summary>
        /// when the request is over, kill the context
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Application_EndRequest(object sender, EventArgs e) {
            NorthwindDBDataContext ctx = HttpContext.Current.Items["RequestContext"] as NorthwindDBDataContext;
           
            // kill it proper-like
            if (ctx != null) {
                ctx.Dispose();
            }
        }

        protected void Application_AuthenticateRequest(object sender, EventArgs e) {

        }

        protected void Application_Error(object sender, EventArgs e) {

        }

        protected void Session_End(object sender, EventArgs e) {

        }

        protected void Application_End(object sender, EventArgs e) {

        }
    }
}

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

dave.dolan

United States United States
Dave works all day, and stays up all night coding and reading, surfing the intertubes.

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