Do while loop in if statement - datareader query

Question

Just wondering if someone can check my do while statement that is nested within an if/elseif statement to see where I'm potentially going wrong.

strSQL = "exec sp_CoursesStartingSoon"
    objConn = New SqlConnection(strConnection)
    objConn.Open()
    objCmd = New SqlCommand(strSQL, objConn)
    datareader = objCmd.ExecuteReader(0)
    datareader.Read()

If (datareader("subjectcode") = "F23") Then

        Do While (datareader("subjectcode") = "F23")

            html += "<h1>Access to HE</h1>"
            html += "<p>" & datareader("name") & "</p>"
            html += "<p>" & datareader("level") & "</p>"

        Loop

    ElseIf (datareader("subjectcode") = "F06") Then

        Do While (datareader("subjectcode") = "F06")

            html += "<h1>Art and Design</h1>"
            html += "<p>" & datareader("name") & "</p>"
            html += "<p>" & datareader("level") & "</p>"

        Loop


    End If

At the moment, the page isn't loading and seems stuck in a loop but wanted to check if its my logic (which I'm assuming it is).

Thanks.

SolidRegardless · Accepted Answer · 2012-11-22 11:36:53Z

2

You are not progressing the datareader after the:

Do While (datareader("subjectcode") = "F23")

Therefore it is continuously reading the same record :)

You need to put a:

datareader.Read()

in the loop somewhere.

If you match any of the F23 or F06 checks, you will stay in the do while loop. Trust me.

EDIT: here you go

    strSQL = "exec sp_CoursesStartingSoon"
    objConn = New SqlConnection(strConnection)
    objConn.Open()
    objCmd = New SqlCommand(strSQL, objConn)
    datareader = objCmd.ExecuteReader(0)

    While datareader.Read()

        If (datareader("subjectcode") = "F23") Then

            html += "<h1>Access to HE</h1>"
            html += "<p>" & datareader("name") & "</p>"
            html += "<p>" & datareader("level") & "</p>"

        ElseIf (datareader("subjectcode") = "F06") Then

            html += "<h1>Art and Design</h1>"
            html += "<p>" & datareader("name") & "</p>"
            html += "<p>" & datareader("level") & "</p>"

        End If

    End While

Just to explain:

To read the next record, you always need to do datareader.Read(). If there are no more records, the API will return false, and exit the loop correctly. You can then check the datareader cursor to see if the current record contains the strings you are looking for. Then when the code loops round again, the datareader.Read() will get the next record for you.

edited Nov 22, 2012 at 11:36

answered Nov 22, 2012 at 11:18

SolidRegardless

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2 Comments

PipBoy Over a year ago

Have I used the wrong logic in the setup of what I'm attempting? Its not obvious to me where I'd need to put another datareader in, in order to progress to the next record.

Steve Over a year ago

It would deserve an upvote if you try to write the corrected code

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