Operator '&' is not defined for string

Question

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VB

Dim conns As New SqlConnection("Data Source=DESKTOP-IJRIL1\SQLEXPRESS;Initial Catalog=Sample_AES;Integrated Security=True")
Dim SubAD As new SqlDataAdapter("Select SubID, Subject From Subjects Where SubID = " & cbSubID.SelectedValue & "", conns)
Dim subtable As New DataTable

SubAD.Fill(subtable)

txtSubject.Text = subtable(0)(1)

What I have tried:

Where SubID = " & cbSubID.SelectedItem.ToString & "", conns)

there is still an error. any suggestions

Posted 25-Apr-19 8:04am

Member 14331592

Updated 25-Apr-19 8:16am

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Comments

Mehdi Gholam 25-Apr-19 14:09pm

Try +

Richard Deeming 25-Apr-19 14:25pm

Dim SubAD As new SqlDataAdapter("Select SubID, Subject From Subjects Where SubID = @SubID", conns)
SubAD.SelectCommand.Parameters.AddWithValue("@SubID", cbSubID.SelectedValue)

Member 14331592 25-Apr-19 14:35pm

tried it but there's an error message about "No mapping exists from object type System.Data.DataRowView to a known managed provider native type."

Richard Deeming 25-Apr-19 14:38pm

Then you'll need to extract the relevant field from the selected item:

Dim SubAD As new SqlDataAdapter("Select SubID, Subject From Subjects Where SubID = @SubID", conns)
Dim row As DataRowView = DirectCast(cbSubID.SelectedValue, DataRowView)
SubAD.SelectCommand.Parameters.AddWithValue("@SubID", row("YOUR_FIELD_NAME_HERE"))

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Dave Kreskowiak · Answer 1 · 2019-04-25T08:16:00

First you don't need the ending & "" garbage. I see that all the time with newb's and it's completely useless.

On your problem line, you start a string literal with a " and then you try to add a variable value to it without first closing the literal.

Next, DO NOT USE string concatenation to build an SQL query. ALWAYS use parameterized queries. See DataAdapter Parameters | Microsoft Docs[^] for how to do it.

Then go see Google: sql injection attack[^] for why.