linq to sql，DataContext中的隔离级别

Question

Need suggestion for the Dbml File with linq , We have database with large amount of data. some times there is lock in table.so we need to apply isolation level with read uncommited (We know some disadvantage for this isolation level)on dbml class.

i have apple below code in dbml file as a partial class

partial class MainDataContext
{
  public MainDataContext()
  {
      base.Connection.BeginTransaction(System.Data.IsolationLevel.ReadUncommitted);
  } 
}

Is it a proper way to implement ? or give any halpfull suggestion on it.

Thanks

Answer 1

If you do that, you will need to attach the transaction to every command on that connection , which isn't something LINQ-to-SQL is going to do for you (although there are ways to make it know about a transaction instance). Perhaps one option is to use the overload that accepts a connection, and simply supply an already-open connection upon which you've already stomped the isolation level via:

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

Of course, if you do that - then it is now your job to dispose the connection properly when you are done: LINQ-to-SQL will assume you are managing the connection lifetime.

Another option with a LINQ-to-SQL data context is to use the ExecuteQuery<T>(sql, args) method, which allows you to pass in your own raw TSQL - this obviously means you aren't really using LINQ any more, but it allows you to add NOLOCK etc in a few places where it makes tactical sense (just using the data-context for the materializer). This is more granular, and allows you to focus on your high throughput / highly concurrent tables.

Answer 2

You can place code that interacts with the db in a TransactionScope block and set the desired Isolation level for the TransactionScope.

TransactionOptions _transactionOptions = new TransactionOptions() { IsolationLevel = IsolationLevel.Snapshot };
using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.Required, _transactionOptions))
{
 //your code here
}

And of course, taking this one step further, you can encapsulate the creation of a transactionScope in a static Factory-like method so that it's easier wherever it's needed and in case you want to change the isolation level there will be one singurla place to change it. Depending on your requirements, choose what's best for you.