How to set isolation level on SqlCommand/SqlConnection initialized with no transaction

Question

The following method is supposed to peroform a dirty read on an open connection. There are no transactions. Where do I set IsolationLevel?

public string DoDirtyRead(string storedProcName, SqlConnection connection)
{
    using (SqlCommand command = new SqlCommand(storedProcName, connection))
    {
        command.CommandType = CommandType.StoredProcedure;
        // HOW TO SET IsolationLevel to READ_UNCOMMITTED here?
        command.ExecuteNonQuery();
    }
}

Answer 1

On the BeginTransaction method: (MSDN link)

And if you just want to use hints in your SP at the table level, use WITH(NOLOCK) - but use at your own risk.

Answer 2

If you don't want to do transactions, you can set it once when you open the connection and it will remain at that setting until you change it. So just do:

connection.BeginTransaction(IsolationLevel.ReadUncommitted).Commit();

Probably not the best for your specific case, since you are opening the connection, using it, and throwing it away, but I wanted to put this answer in for anyone with a longer-lived connection.

Answer 3

In your Stored Procedure, for transact-sql use:

SET TRANSACTION ISOLATION LEVEL read uncommitted    -- 0
SET TRANSACTION ISOLATION LEVEL read committed     -- 1
SET TRANSACTION ISOLATION LEVEL repeatable read    -- 2
SET TRANSACTION ISOLATION LEVEL read serializable  -- 3

Answer 4

Given you already have an existing connection (and possibly an existing transaction), I'd use a TransactionScope to control the isolation level of the child. This does a dirty read rowcount (I believe):

using (var command = connection.CreateCommand())
using(new TransactionScope(TransactionScopeOption.RequiresNew, new TransactionOptions{IsolationLevel = IsolationLevel.ReadUncommitted}))
{
    command.CommandText = string.Format("select count(*) from {0}", tableName);
    return (int)command.ExecuteScalar();
}

Answer 5

Add another parameter to your stored procedure to indicate the isolation level you want the stored procedure to run with.

IF @isolevel = 0 SET TRANSACTION ISOLATION LEVEL read uncommitted; ELSE

Also I believe uncommitted needs two "t's" in it.