Dialect/Driver - Every SELECT I perform, add with(nolock)

Question

I need to know a way to implement in my system, a Driver or Dialect which, whenever I perform a SELECT in Nhibernate, the SELECT adds the with(nolock) with it. I need that t

Answer 1

Using the WITH(NOLOCK) hint is the same thing as using a READ UNCOMMITED transaction isolation level as discussed here: When should you use "with (nolock)".

You can specify the transaction isolation level when starting new transactions with NHibernate:

var session = SessionFactory.OpenSession();
session.BeginTransaction(IsolationLevel.ReadUncommitted);

I would not recommend this unless you really know what you are doing though. Here's some more information on the subject: Why use a READ UNCOMMITTED isolation level?.

Answer 2

Hope this would help someone, I used this code to add no lock hints to the most of the queries, related to the answer dillenmeister

public class NoLockHintsInterceptor : EmptyInterceptor
    {
        public override SqlString OnPrepareStatement(SqlString sql)
        {
            // Modify the sql to add hints
            if (sql.StartsWithCaseInsensitive("select"))
            {
                var parts = new List<object>((object[]) sql.Parts);
                object fromItem = parts.FirstOrDefault(p => p.ToString().ToLower().Trim().Equals("from"));
                int fromIndex = fromItem != null ? parts.IndexOf(fromItem) : -1;
                object whereItem = parts.FirstOrDefault(p => p.ToString().ToLower().Trim().Equals("where"));
                int whereIndex = whereItem != null ? parts.IndexOf(whereItem) : parts.Count;

                if (fromIndex == -1)
                    return sql;

                parts.Insert(parts.IndexOf(fromItem) + 2, " with(nolock) ");
                for (int i = fromIndex; i < whereIndex; i++)
                {
                    if (parts[i - 1].Equals(","))
                    {
                        parts.Insert(i + 2, " with(nolock) ");
                        i += 2;
                    }
                    if (parts[i].ToString().Trim().EndsWith(" on"))
                    {
                        parts[i] = parts[i].ToString().Replace(" on", " with(nolock) on ");
                    }
                }
                sql = new SqlString(parts.ToArray());
            }
            return sql;
        }
    }

Answer 3

There are two errors in this code:

1. For SQL script that has parameter This code won't work.
2. SqlString.Parts is not compile, I am using NHibernate 4.0.0.4000

Here is the Fix:

---

public class NoLockInterceptor : EmptyInterceptor
{
    public override SqlString OnPrepareStatement(SqlString sql)
        {
            //var log = new StringBuilder();
            //log.Append(sql.ToString());
            //log.AppendLine();

            // Modify the sql to add hints
            if (sql.StartsWithCaseInsensitive("select"))
            {
                var parts = sql.ToString().Split().ToList();
                var fromItem = parts.FirstOrDefault(p => p.Trim().Equals("from", StringComparison.OrdinalIgnoreCase));
                int fromIndex = fromItem != null ? parts.IndexOf(fromItem) : -1;
                var whereItem = parts.FirstOrDefault(p => p.Trim().Equals("where", StringComparison.OrdinalIgnoreCase));
                int whereIndex = whereItem != null ? parts.IndexOf(whereItem) : parts.Count;

                if (fromIndex == -1)
                    return sql;

                parts.Insert(parts.IndexOf(fromItem) + 3, "WITH (NOLOCK)");
                for (int i = fromIndex; i < whereIndex; i++)
                {
                    if (parts[i - 1].Equals(","))
                    {
                        parts.Insert(i + 3, "WITH (NOLOCK)");
                        i += 3;
                    }
                    if (parts[i].Trim().Equals("on", StringComparison.OrdinalIgnoreCase))
                    {
                        parts[i] = "WITH (NOLOCK) on";
                    }
                }
                // MUST use SqlString.Parse() method instead of new SqlString()
                sql = SqlString.Parse(string.Join(" ", parts));
            }

            //log.Append(sql);
            return sql;
        }
}

Answer 4

It is possible to modify the sql using an Interceptor and overriding the OnPrepareStatement method, something like this:

public class AddNoLockHintsInterceptor : EmptyInterceptor
{
    public override SqlString OnPrepareStatement(SqlString sql)
    {
        // Modify the sql to add hints

        return sql;
    }
}

And here is a way to register the interceptor with NHibernate:

var session = SessionFactory.OpenSession(new AddNoLockHintsInterceptor());