Question

is it ok to use something like this in the web:
(my application is on asp.net mvc)

public static class DbUtil
{  
      public static int Insert(object o, string cs)
        {
            using (var conn = new SqlConnection(cs))
            using (var cmd = conn.CreateCommand())
            {
              ...

                conn.Open();
                return Convert.ToInt32(cmd.ExecuteScalar());
            }
        }
}

usage:

public class Repository<T> : IRepository<T>
{
       public virtual int Insert(T o)
       {
            return DbUtil.Insert(o, Cs);
       }
}

and after constructor injection in the service or controller

    public MyController(
        IRepository<Organization> organizationRepository)
    {
        this.organizationRepository = organizationRepository;
    }

Answer 1

It is absolutely OK to use this static class as long as it is hidden and wrapped behind the repository as it is in your case. This allows weaker coupling between the controller logic using the repository and the data access. The static method you’ve shown seems perfectly reentrant which makes it thread safe.