Question

当我运行这段代码时，我收到错误：

尚未初始化ExecuteScalar连接属性

我似乎无法找到连接无效的原因。

代码：

Protected Sub btnTrackRepair_Click(sender As Object, e As EventArgs) Handles btnTrackRepair.Click

    Using conn As New SqlConnection("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\ITrepair.mdf;Integrated Security=True")
        conn.Open()
        Dim cmd As New SqlCommand(conn.ToString)
        Dim txtTracking As String
        cmd.CommandText = "SELECT Repair_Status FROM Repair WHERE Tracking_Number =" & txtTrack.Text
        txtTracking = If(IsDBNull(cmd.ExecuteScalar), "", cmd.ExecuteScalar)
        If txtTracking <> "" Then
            MsgBox("Record Found!", MsgBoxStyle.Information, "Update")
            txtStatus.Text = ""
            txtStatus.Text = txtTracking
        Else
            MsgBox("No Record Found!", MsgBoxStyle.Information, "INFO.")
        End If
    End Using

End Sub

代码在txtTracking = If(IsDBNull(cmd.ExecuteScalar), "", cmd.ExecuteScalar)

处中断

我已经查看了有关此错误的其他问题，但大多数是C＃，我使用的是VB.NET，因此我发现很难找到解决方案。

Answer 1

您正在使用仅占用字符串的SqlCommand constructor。但这不是连接字符串，而是查询的文本。所以你做错了。

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.RadioButton;
import javafx.scene.control.Toggle;
import javafx.scene.control.ToggleGroup;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Test extends Application{

    @Override
    public void start(Stage primaryStage) throws Exception {
        GridPane root = new GridPane();
        root.setAlignment(Pos.CENTER);
        root.setHgap(20);
        VBox container = new VBox();
        container.setAlignment(Pos.CENTER);

        final ToggleGroup group = new ToggleGroup();
        RadioButton rb1 = new RadioButton("First Choice");
        rb1.setToggleGroup(group);
        RadioButton rb2 = new RadioButton("Second Choice");
        rb2.setToggleGroup(group);
        RadioButton rb3 = new RadioButton("Third Choice");
        rb3.setToggleGroup(group);

        container.getChildren().addAll(rb1,rb2,rb3);

        Button btn = new Button("I should appear");
        btn.setVisible(false);

        root.add(container, 0, 0);
        root.add(btn, 1, 0);

        group.selectedToggleProperty().addListener(new ChangeListener<Toggle>(){
            public void changed(ObservableValue<? extends Toggle> ov,
                 Toggle old_toggle, Toggle new_toggle) {
                    if (group.getSelectedToggle() != null) {
                        btn.setVisible(true);
                    }                
                }
        });

        Scene s = new Scene(root,400,200 );
        primaryStage.setScene(s);
        primaryStage.setResizable(false);
        primaryStage.setTitle("Example");
        primaryStage.show();    


    }

    public static void main(String[] args){
        launch();
    }

}

除此之外，您应该熟悉参数化查询。不要使用字符串连接来构建查询以避免（除其他问题）sql注入攻击。

这是完整的方法：

Dim cmd As New SqlCommand("SELECT Repair_Status FROM Repair WHERE Tracking_Number = @Tracking_Number", conn)

如果数据库中的Protected Sub btnTrackRepair_Click(sender As Object, e As EventArgs) Dim sqlQuery = "SELECT Repair_Status FROM Repair WHERE Tracking_Number = @Tracking_Number" Using conn As New SqlConnection("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\ITrepair.mdf;Integrated Security=True") conn.Open() Dim cmd As New SqlCommand(sqlQuery, conn) cmd.Parameters.Add("@Tracking_Number", SqlDbType.NVarChar).Value = txtTrack.Text Dim statusObj = cmd.ExecuteScalar() Dim status = If(statusObj is DBNull.Value, Nothing, DirectCast(statusObj, string)) If not String.IsNullOrEmpty(status) Then MsgBox("Record Found!", MsgBoxStyle.Information, "Update") ' ... ' Else MsgBox("No Record Found!", MsgBoxStyle.Information, "INFO.") End If End Using End Sub不是varchar / nvarchar而是Tracking_Number（例如），则应该在此解析它并使用正确的int。

ExecuteScalar连接属性尚未初始化

1 个答案: