Where to use connection, dataset, datareader ?

  • Thread starter Thread starter Doru Roman
  • Start date Start date
D

Doru Roman

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.
 
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.
 
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
 
Thanks Sahil and William :)

Marina Levit said:
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.
Click to expand...
 
Thank you Cor :)

Cor Ligthert said:
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
Click to expand...
 
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