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.NET Forum / .NET Framework / ADO.NET / January 2006Where to use connection, dataset, datareader ?
Hi, I have some difficulties in understanding how to use the connection, dataset, datareader in a form. Let's suppose I want to create a datareader and when I push a button to bring another row from the dataset. Supposedly I create under MyForm_Load event the connection, then a command and the reader. SqlConnection conn = new SqlConnection(...); conn.open(); SqlCommand cmd = conn.CreateCommnad(); cmd.CommandType = ... cmdCommnadText = .... SqlReader dr = cmd.ExecuteReader(); If I try to use dr.Read() in side a ButtonRead_Click event, dr is not recognized. So, what is the approach here, where I create and use the components to make them work? Thanks, Doru This is an issue of scope. Variables declared locally in a function cannot be referenced outside that function. If something needs to be accessed in multiple functions, it should be declared as a member variable of the class. In the case of a data reader, I would not recommend having it be a class level variable. For it to be of any use it would need to maintain an open database connection, and that is not advisable. I would say just open the connection in your click event as needed, run your query, get your data, close the connection - all within the click event. The problem you are describing is not actually related to ADO.NET in any way, but in not understanding variable scoping. I recommend you pick up a book on C# and read up on its structure and some coding techniques. > Hi, > [quoted text clipped - 18 lines] > Thanks, > Doru I realize it is a matter of scope, that is why I asked for a solution in case I need to navigate through the records at a push of a button. I gather that this is not possible. I told you how you can do it - declare the variables not inside a particular function, but at the class level. So it's not impossible. I just warned against having an open data reader just sitting around on a form, that is a bad database access practice. >I realize it is a matter of scope, that is why I asked for a solution in >case I need to navigate through the records at a push of a button. I gather >that this is not possible. Hey Marina, Are you the Marina we've been seeing in this NG for so long now? If so, I'm happy you got MVP :). Congrats and well deserved indeed. - Sahil Malik [MVP] ADO.NET 2.0 book - http://codebetter.com/blogs/sahil.malik/archive/2005/05/13/63199.aspx ---------------------------------------------------------------------------- >I told you how you can do it - declare the variables not inside a >particular function, but at the class level. So it's not impossible. I [quoted text clipped - 4 lines] >>case I need to navigate through the records at a push of a button. I >>gather that this is not possible. Oh, and yeah, same Marina :) > Hey Marina, > [quoted text clipped - 14 lines] >>>case I need to navigate through the records at a push of a button. I >>>gather that this is not possible. Marina: I noticed the same thing Sahil did. It's an honor to have you on board! >I told you how you can do it - declare the variables not inside a >particular function, but at the class level. So it's not impossible. I [quoted text clipped - 4 lines] >>case I need to navigate through the records at a push of a button. I >>gather that this is not possible. Thanks Sahil and William :) >I told you how you can do it - declare the variables not inside a >particular function, but at the class level. So it's not impossible. I [quoted text clipped - 4 lines] >>case I need to navigate through the records at a push of a button. I >>gather that this is not possible. I declared the datareader as a variable of the Form class and it works. > This is an issue of scope. Variables declared locally in a function cannot > be referenced outside that function. If something needs to be accessed in [quoted text clipped - 33 lines] >> Thanks, >> Doru Marina, I am happy for the recognition of your work. Although that you was for me of course already onboard of these newsgroups is it always nice to see as others as well award you for that. My congratulations, Cor > This is an issue of scope. Variables declared locally in a function cannot > be referenced outside that function. If something needs to be accessed in [quoted text clipped - 33 lines] >> Thanks, >> Doru Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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