如何在多用户环境中更新/删除行

Question

I am new to C# and SQL Server .

I am developing an application using Winforms .

I am using dataset .

In master and details transactions, suppose I retrieve one transaction from the database. At the same time another user also retrieves the same transaction.

My requirement is when I am changing this transaction no one else should be allowed to update or delete the same transaction.

As dataset is in disconnect mode, how can I achieve the locking mechanism?

Answer 1

If im correct in assuming you are using C# then you should look into some ORM frameworks as they can handle collisions like this for you or at least alert you when they have happened so you can handle them in your code. So you could for instance inform the user someone else has made a change and refresh their display or merge the changes and save the merged data.

Have a look at entity framework. There are literally loads of tutorials and examples available for you. This should get you started.

http://www.asp.net/entity-framework

http://msdn.microsoft.com/en-us/library/bb386876.aspx

This specifically references data concurrency (its MVC but the principles are the same)

http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/handling-concurrency-with-the-entity-framework-in-an-asp-net-mvc-application

Answer 2

using (var transaction = connection.BeginTransaction())
{

  adapter.Update(dataSet); 

  transaction.Commit();
}

If the update is to a small number of rows within a table, SQL server grants a row level lock to the caller. If the change is to a large number of rows, SQL server grants a table level lock. Its all automatic. Hence concurrency is taken care of.

The problem however is that with many users simultaneously working on the same set of rows, chance of a dead lock are high. The new CQRS design pattern promoted by Udi Dahan takes care of that. How ever if your application is small, applying CQRS would be an overkill.