Tuesday, April 20, 2010

Creating a Video Sharing Library


First step to create a video sharing library we need to have all videos in a FLV flash format in order to play them on webpage,
Sounds familiar, yeah the famous youtube.com does that, how exactly we can do something similar to youtube?

 How to convert files uploaded by people in FLV format?


There are different open source tools available for converting different formats of videos to other formats, unfortunately there are issues and bugs in these tools, and less support,  we can not use one tool for convert videos in FLV format, we have to mix two different tools for this purpose, below are the steps how can we achieve that using FFMPEG and FLVTOOL.

Step # 1:

Download FFMPEG (search it on Google, download it build it)
Download FLVTOOL (search it on Google, download it build it)
Or simply download my pre build copy from
·    
sample.3gp
http://www.filefactory.com/file/b131a99/n/sample.3gp
FFmpeg_FLVTOOL.rar
http://www.filefactory.com/file/b131aa7/n/FFmpeg_FLVTOOL.rar
beelden.zip
http://www.filefactory.com/file/b131bgf/n/beelden.zip
Extract following in a folder, (I supposed d:\ffmpeg folder)

Step # 2:

Run following command-line commands form your programming language exp C#.

1)      Convert to AVI first because some formats are not directly convert able into FLV
D:\FFmpeg>ffmpeg -i sample.3gp -s 470X320 -ar 44100 s22.avi
2)      Take snap from video file
D:\FFmpeg>ffmpeg -i s22.avi -ss 3 t11.jpg
3)      Convert to required FLV format
D:\FFmpeg>ffmpeg -i s22.avi -s 470X320 t11.flv
4)      fix errors using flvtool
D:\FFmpeg\>flvtool2 -UP t11.flv out2.flv

Step # 3

Download FW flash player (search it from Google)
Extract it into the same folder

Step # 4

Create a new HTML file and paste and save the following code:
<html>
<body>
<script type='text/javascript' src='swfobject.js'><script>
<div id='Div1' style="border:solid:2px:black">
    <div id='mediaspace'>This text will be replaced<div>
<div>
<script type='text/javascript'>
  var so = new SWFObject('player.swf','ply','468','348','9','#ffffff');
  so.addParam('allowfullscreen','true');
  so.addParam('allowscriptaccess', 'always');
  so.addVariable('image', 't11.jpg');
  so.addVariable('skin', 'beelden.zip');
  so.addParam('wmode','opaque');
  so.addVariable('file','out2.flv');
  so.write('mediaspace');
<script>
<body>
<html>

Step # 5

Preview your newly saved HTML in web browser.









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Wednesday, April 14, 2010

Implementation of SQL IN clause in LINQ


To implement SQL IN clause in LINQ there are 4 steps


1.       GetTable from  which you need to filter rows.
2.       GetTable that contains the values(only one clumn) you need to match in IN clause.
3.       Type cast data of step # 2 DataTable column data identical to step # 1 DataTable filtering column/property.
4.       Use step# 2 DataTable’s Contains() method of step # 1 DataTable’s where caluse

public List<CustomerCoupon> getCustomerNonSpecials(int StoreID, int customerID)
        {
           
           
//Step # 1
List<CustomerCoupon> coupons = new List<CustomerCoupon>();
coupons = customerCouponsTable.Where(coupon => coupon.Customer.CustomerID == customerID).ToList();
           

//Step # 2
Table<CategoryItem> specialsTable = customersTable.Context.GetTable<CategoryItem>();
            Table<CustomerCoupon> customerCouponsTable = customersTable.Context.GetTable<CustomerCoupon>();
List<CategoryItem> specials = new List<CategoryItem>();
specials = specialsTable.Where(cItem => cItem.StoreCategory.CategoryName == cItem.Item.Store.StoreCategorys[0].CategoryName && cItem.Item.Store.StoreID == StoreID).ToList();

var query = from c in coupons
join s in specials on c.ItemID equals s.ItemID
      select new { c.Item.ItemID };

//Step # 3           
List<int> SpecialsCouponsIDs = new List<int>();
SpecialsCouponsIDs = query.ToList().ConvertAll<int>(i=> Convert.ToInt16(i.ItemID));

//Step # 4
List<CustomerCoupon> nonSpecialsCoupons =new List<CustomerCoupon>();
nonSpecialsCoupons = (from c in coupons where SpecialsCouponsIDs.Contains(c.ItemID) select c).ToList();
return nonSpecialsCoupons;
}
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Pessimistic and optimistic locking


Transactional isolation is usually implemented by locking whatever is accessed in a transaction. There are two different approaches to transactional locking: Pessimistic locking and optimistic locking.
The disadvantage of pessimistic locking is that a resource is locked from the time it is first accessed in a transaction until the transaction is finished, making it inaccessible to other transactions during that time. If most transactions simply look at the resource and never change it, an exclusive lock may be overkill as it may cause lock contention, and optimistic locking may be a better approach. With pessimistic locking, locks are applied in a fail-safe way. In the banking application example, an account is locked as soon as it is accessed in a transaction. Attempts to use the account in other transactions while it is locked will either result in the other process being delayed until the account lock is released, or that the process transaction will be rolled back. The lock exists until the transaction has either been committed or rolled back.

Pessimistic locking in ADO.NET

One way to deal with optimistic concurrency issues in ADO.NET is to lock records as they are retrieved from the data source. It doesn't take much code, but it does involve some risks. Find out when you should use this procedure and how it works.

Six steps to implement Pessimistic Locking in ADO.NET

Create a transaction by using IsolationLevel of RepeatableRead.
Set the DataAdapter’s SelectCommand property to use the transaction we have created in step #1.
Make the changes to the data.
Set DataAdapter’s Insert, Update, and Delete command properties to use the transaction created in step #1.
Call the DataAdapter’s Update method.
Commit the transaction.

Below is an example using pessimistic locking by using ADO.NET, developer just need to create object of the class mentioned below, select data in DataSet, update it with required changes, then call submitChanges method to save it into database, by using pessimistic locking procedure.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Data.Common;
using System.Data;

namespace Locking_example
{
    public class DAL
    {
        private String CommandText;
        private SqlConnection ObjSqlConnection;
        private SqlDataAdapter ObjSqlDataAdapter;
        private String connectionString;
        private DataSet Ds;
        private SqlTransaction ObjSqlTransaction;
       
        //Constructor
        public DAL(String ConnectionString)
        {
            this.connectionString = ConnectionString;
            ObjSqlConnection = new SqlConnection(this.connectionString);
            ObjSqlDataAdapter = new SqlDataAdapter();

        }

        public DataSet select(String commandText)
        {
            ObjSqlConnection.Open();
            ObjSqlTransaction = ObjSqlConnection.BeginTransaction(IsolationLevel.RepeatableRead);
            ObjSqlDataAdapter.SelectCommand.CommandText=this.CommandText;
            ObjSqlDataAdapter.SelectCommand.Transaction = ObjSqlTransaction;
            ObjSqlDataAdapter.Fill(Ds);
            return Ds;
        }
        public bool SubmitChanges(DataSet Ds)
        {
            try
            {
                ObjSqlDataAdapter.InsertCommand.Transaction = ObjSqlTransaction;
                ObjSqlDataAdapter.UpdateCommand.Transaction = ObjSqlTransaction;
                ObjSqlDataAdapter.DeleteCommand.Transaction = ObjSqlTransaction;
                ObjSqlDataAdapter.Update(Ds);
                ObjSqlTransaction.Commit();
                ObjSqlConnection.Close();
                return true;
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

    }
}

Pessimistic locking in LINQ to SQL

Pessimistic locking is pre-implemented in LINQ to SQL, however we need to user TransactionScope class in order to use pessimistic locking.
If two different instances of same program trying to update a data rows set (collection of LINQ  objects) or even different programs, first program who ever update the selected data will be saved in database, reset of others will get following exception :
Unhandled Exception: System.Data.Linq.ChangeConflictException: Row not found or changed.

Because of the fact that before updating LINQ to SQL first tried to select the same row using a where clause with all old values.
Below is an example of using pessimistic locking using LINQ to SQL and TransactionScope
using (TransactionScope ts = new TransactionScope())
                {



                    Customer newCustomer = new Customer
                    {
                        FirstName = "To be Updated",
                        LastName = "To be Updated",
                        State = "To be Updated",
                        ZipCode = "To be Updated",
                        City = "To be Updated",
                        Address1 = "To be Updated",
                        Address2 = "To be Updated",

                    };
                    customersTable.InsertOnSubmit(newCustomer);
                    try
                    {
                        this.SubmitChanges();
                    }
                    catch (Exception ex)
                    {
                        return null;
                    }
                    CustomerStoreConfiguration newCustomerStoreConfiguration = addSignupConfigurations(newCustomer, storeID, cellPhoneNumber, pin);
                    if (newCustomerStoreConfiguration == null)
                    {
                        ts.Dispose();
                        return null;
                    }
                    ts.Complete();
                    return newCustomerStoreConfiguration;
                }
            }
        }
       
        public void SubmitChanges()
        {
            customersTable.Context.SubmitChanges();
        }

public CustomerStoreConfiguration addSignupConfigurations(Customer newCustomer, int storeID, string cellphoneNumber, string pin)
        {
            Table<CustomerStoreConfiguration> CustomerStoreConfigurationTable = customersTable.Context.GetTable<CustomerStoreConfiguration>();
            CustomerStoreConfiguration newCustomerStoreConfiguration = new CustomerStoreConfiguration
            {
                CellPhoneNumber = cellphoneNumber,
                StoreID = storeID,
                PIN = pin,
                CustomerID = newCustomer.CustomerID,
                EmailAddress = "To_Be_Updated@updateMe.now",
                EnableAllCatelogPromotions = false,
                EnableAllEmailPromotions = false,
                EnableAllRetailFlyerPromotions = false,
                EnableCatelogPromotions = false,
                EnableRetailFlyerPromotions = false,
                EnableSpatialEmailPromotions = false,
                MaxCatelogPromotions = 0,
                MaxEmailPromotions = 0,
                MaxRetailFlyerPromotions = 0,
                MaxMobilePromotions=0
            };
            CustomerStoreConfigurationTable.InsertOnSubmit(newCustomerStoreConfiguration);

            try
            {
                CustomerStoreConfigurationTable.Context.SubmitChanges();
                return newCustomerStoreConfiguration;
            }
            catch (Exception ex)
            {
                return null;
            }
           
        }

Incase of voilation of pessimistic locking user may encounter follwing exception:
Unhandled Exception: System.Data.SqlClient.SqlException: Transaction (Process ID 52) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.





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