ADO.Net

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  15 years ago

  by sunilbenjamin

  Sunil

  , United States

  Joined 15 years ago

  
  I am a Newbie in dot Net..so am really sorry if you feels that my doubt is too kiddish
  ADO.Net is a disconnected database architecture with Dataset as the core object in its object hierarchy.
  

  
  For explaining my doubt, I am taking an example of a table named "Employee" in the database named "Company
  Employee table has an autonumberd primary key column "EmployeeID"
  

  
  Consider a networked  multiuser environment or Internet itself.
  

  
  Suppose Employee table has 10 rows in it. A user named "A" retrieves all of the rows and caches in his client side Dataset.
  He then deleted the 10th row and then started editing some of the columns in the 9th row.
  He then adds 11th row with the primary key "EmployeeID"  (lets say 100 as the next autonumber generated. So the new record he created as 100 as the "EmployeeID")
  

  
  These changes hasnt yet been physically updated to the database.
  

  
  

  
  At this same point of time another user named "B" extracted the employee table rows from the database and cached in his client side Dataset.First he deleted the 9th row and started editing the 10th row's data. then
  adds 11th row . Since the above changes hasnt been yet updated to the database, the new row created by B also has 100 as the  primary key(autonumber)..
  

  
  

  
  {    Even if the primary key is not auto number, let me say that incidently both of them gave 100 as the primary key value for the new rows they created    }
  

  
  Now from this moment..let me say.. first the user B calls the Dataset.Update method and after tht User B calls the Dataset.Update method.
  

  
  Can anybody explain me what exactly hapens in database whn both of the statements executed?..
  

  
  Is it that all the valuable data which A has edited in 9th row has gone ??..so as B has edited the 10th row???.. wil it be an
  incosistent database?..Then what abt the new row both has added with the same primary key value???
  

  
  

  
  Can anybody explain me these anamolies please??
  

  
  

  
  Another doubt is, we can create a sequence in Oracle database.  Can i make it available in a dataset ???

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  15 years ago

  by VasanthKumar

  vas

  Kerala,Cochin,India, India

  Joined 15 years ago

  from my understanding of u r problem what will happen here is
  

  
  u have set one columnas primary key in the database
  then u cannot update 2 rows with the same id
  

  
  hare if A has called the update first then A's update will be valid
  then B called the Update Method then on saving it would give error
  

  
  there is 2 event in sqldataadapter
  

  
  SqlDataAdapter1RowUpdated
  SqlDataAdapter1RowUpdating
  

  
  here u can see the rows getting updating its state everything
  

  
  

  
  in u r case what u can do is
  put a Catch xyz As System.Data.SqlClient.SqlException
  just below the update satement.
  

  
  see this
  Try
  

  
             SqlDataAdapter1.Update(ds)
           Catch xyz As System.Data.SqlClient.SqlException
         Catch ex As Exception
  

  
         End Try
  

  
  and automatically a small error symbol will be shown next to that duplicate row.
  

  
  ie xyz will show similar message
     xyz.message    "Violation of PRIMARY KEY constraint 'PK_Employees'. Cannot insert duplicate key in object 'Employees'."    String
  

  
  

  
  2
  Another doubt is, we can create a sequence in Oracle database.  Can i make it available in a dataset ???
  

  
  yes u can set the seed ie theway it should be incremented and atrting value of like
  

  
  AutoIncrement()
  AutoIncrementSeed()
  

  
  

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