Handling DBNull.Value
Every asp.net developer use DbNull.Value when writing code to communicate with database. But it could sometimes be quite painful when you want to write with a null-coalescing or ?: operator. The same would be when getting something from database and type checking.
For example in this code snippet I wrote a function which stores a comment in database. As userWebsite is an optional parameter so it could be null and if database expects null then you need to send DBNull.Value. To make it adjustable in ?: operator you just have to cast into an object. like;
Value = userWebsite != null ? userWebsite : (object)DBNull.Value.
I tested this code in fw 4.0 only, so I’m not sure about older versions.
internal int SaveComment(string name, string email, string comment, string? userWebsite) { SqlCommand _command = new SqlCommand { Connection = new SqlConnection { ConnectionString = "connection string" }, CommandType = CommandType.StoredProcedure, CommandText = "csp_comment_save", }; _command.Parameters.AddRange(new SqlParameter[] { new SqlParameter { ParameterName = "name", Value = name, SqlDbType = SqlDbType.VarChar, Size = 100 }, new SqlParameter { ParameterName = "email", Value = email, SqlDbType = SqlDbType.VarChar, Size = 50 }, new SqlParameter { ParameterName = "comment", Value = comment, SqlDbType = SqlDbType.VarChar, Size = 255 }, new SqlParameter { ParameterName = "website", Value = userWebsite != null ? userWebsite : (object)DBNull.Value, SqlDbType = SqlDbType.VarChar, Size = 20 }}); _command.Connection.Open(); int result=_command.ExecuteNonQuery(); _command.Connection.Close(); return result; }
Categories: asp.net features, Best Practices of ASP.Net
:? operator, DBNull.Value
Thanks for this article it’s good, but it’s not working for my MS Chart control. If you have any idea about this then, please let me know. My page has a simple MS chart control which needs to be printed as well. When I pass the html of the control to convert, it throws error. Hope you would reply soon. Thanks.
Are you trying to convert html to pdf, or something else? Because your comment appeared on a post which is not directly related to html.
If so then, did you try the sample project ? I can’t say for sure of the error because I don’t know of your html structure. One thing I can say your html should be syntactically correct .