发生异常时显示警告消息

Question

我有一个网络服务，可以插入、删除、更新数据库中的数据。所以在这种特殊形式中，它有一个外键。所以基本上它应该只接受primarty表中存在的值。 当用户输入任何其他值时，就会发生异常。

如何确保在捕获此类 SQL 异常时，从我的 Web 服务传递用户友好的自定义错误消息（例如输入的 ID 不存在。数据插入失败！）。

非常感谢。

Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.ComponentModel
Imports System
Imports System.Collections.Generic
Imports System.Configuration
Imports System.Data.SqlClient
Imports System.Web.Script.Serialization
Imports System.Web.Script.Services

' To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
<System.Web.Script.Services.ScriptService()>
<System.Web.Services.WebService(Namespace:="http://tempuri.org/")>
<System.Web.Services.WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)>
<ToolboxItem(False)>
Public Class WebService2
    Inherits System.Web.Services.WebService


    Public Class Details

        Public Property CardID As Integer
        Public Property BookID As Integer
        Public Property IssuedBy As String

    End Class






    <WebMethod>
    Public Sub AddBook(ByVal emp As Details)
        Dim cs1 As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString
        Using con1 As SqlConnection = New SqlConnection(cs1)



            Dim thequery As String = "select * from BookIssue where CardID=@CardID"
            Dim cmd1 As SqlCommand = New SqlCommand(thequery, con1)
            cmd1.Parameters.Add(New SqlParameter() With {
                .ParameterName = "@CardID",
                .Value = emp.CardID
            })

            con1.Open()

            Dim reader As SqlDataReader = cmd1.ExecuteReader()



            If reader.HasRows Then
                MsgBox("ID Number is Already in use")
                con1.Close()

            Else


                Dim cs As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString

                Using con As SqlConnection = New SqlConnection(cs)
                    Dim cmd As SqlCommand = New SqlCommand("spInsertIntoBookIssue", con)
                    cmd.CommandType = CommandType.StoredProcedure


                    cmd.Parameters.Add(New SqlParameter() With {
                        .ParameterName = "@CardID",
                        .Value = emp.CardID
                    })
                    cmd.Parameters.Add(New SqlParameter() With {
                        .ParameterName = "@BookID",
                        .Value = emp.BookID
                    })

                    cmd.Parameters.Add(New SqlParameter() With {
                       .ParameterName = "@IssuedBy",
                       .Value = emp.IssuedBy
                   })
                    con.Open()
                    cmd.ExecuteNonQuery()


                    MsgBox("Data Inserted")



                End Using
            End If
        End Using
    End Sub

    <WebMethod>
    Public Sub GetAllDetails()
        Dim listEmployees As List(Of Details) = New List(Of Details)()
        Dim cs As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString

        Using con As SqlConnection = New SqlConnection(cs)
            Dim cmd As SqlCommand = New SqlCommand("Select * from BookIssue", con)
            con.Open()
            Dim rdr As SqlDataReader = cmd.ExecuteReader()

            While rdr.Read()
                Dim details As Details = New Details()
                details.CardID = Convert.ToInt32(rdr("CardID"))
                details.BookID = Convert.ToInt32(rdr("BookID"))
                details.IssuedBy = rdr("IssuedBy").ToString()

                listEmployees.Add(details)
            End While
        End Using

        Dim js As JavaScriptSerializer = New JavaScriptSerializer()
        Context.Response.Write(js.Serialize(listEmployees))
    End Sub

    <WebMethod>
    Public Sub GetAllDetails1()
        Dim listEmployees As List(Of Details) = New List(Of Details)()
        Dim cs As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString

        Using con As SqlConnection = New SqlConnection(cs)
            Dim cmd As SqlCommand = New SqlCommand("Select * from BookIssue", con)
            con.Open()
            Dim rdr As SqlDataReader = cmd.ExecuteReader()

            While rdr.Read()
                Dim details As Details = New Details()
                details.CardID = Convert.ToInt32(rdr("CardID"))
                details.BookID = Convert.ToInt32(rdr("BookID"))
                details.IssuedBy = rdr("IssuedBy").ToString()

                listEmployees.Add(details)
            End While
        End Using

        Dim js As JavaScriptSerializer = New JavaScriptSerializer()
        Context.Response.Write(js.Serialize(listEmployees))
    End Sub
    <WebMethod>
    Public Function GetdetailsById(ByVal CardID As Integer) As Details
        Dim details As Details = New Details()
        Dim cs As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString

        Using con As SqlConnection = New SqlConnection(cs)
            Dim cmd As SqlCommand = New SqlCommand("spGetBookIssueDetailsByCardID", con)
            cmd.CommandType = CommandType.StoredProcedure
            Dim parameter As SqlParameter = New SqlParameter()
            parameter.ParameterName = "@CardID"
            parameter.Value = CardID
            cmd.Parameters.Add(parameter)
            con.Open()
            Dim rdr As SqlDataReader = cmd.ExecuteReader()

            While rdr.Read()
                details.CardID = Convert.ToInt32(rdr("CardID"))
                details.BookID = Convert.ToInt32(rdr("BookID"))
                details.IssuedBy = rdr("IssuedBy").ToString()

            End While
        End Using

        Return details
    End Function


    <WebMethod>
    Public Function GetdetailsById1(ByVal CardID As Integer) As Details
        Dim details As Details = New Details()
        Dim cs As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString

        Using con As SqlConnection = New SqlConnection(cs)
            Dim cmd As SqlCommand = New SqlCommand("spGetBookIssueDetailsByCardID1", con)
            cmd.CommandType = CommandType.StoredProcedure
            Dim parameter As SqlParameter = New SqlParameter()
            parameter.ParameterName = "@CardID"
            parameter.Value = CardID
            cmd.Parameters.Add(parameter)
            con.Open()
            Dim rdr As SqlDataReader = cmd.ExecuteReader()

            While rdr.Read()
                details.CardID = Convert.ToInt32(rdr("CardID"))
                details.BookID = Convert.ToInt32(rdr("BookID"))
                details.IssuedBy = rdr("IssuedBy").ToString()

            End While
        End Using

        Return details
    End Function




    <WebMethod>
    Public Sub DeleteRecord1(ByVal emp As Details)
        Dim cs As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString

        Using con As SqlConnection = New SqlConnection(cs)
            Dim cmd As SqlCommand = New SqlCommand("spDeleteByID", con)
            cmd.CommandType = CommandType.StoredProcedure
            cmd.Parameters.Add(New SqlParameter() With {
                .ParameterName = "@CardID",
                .Value = emp.CardID
            })

            con.Open()
            cmd.ExecuteNonQuery()
        End Using
    End Sub

    <WebMethod>
    Public Sub Update(ByVal emp As Details)
        Dim cs As String = ConfigurationManager.ConnectionStrings("library management systemConnectionString").ConnectionString

        Using con As SqlConnection = New SqlConnection(cs)
            Dim cmd As SqlCommand = New SqlCommand("spUpdateBookIssue", con)
            cmd.CommandType = CommandType.StoredProcedure

            cmd.Parameters.Add(New SqlParameter() With {
               .ParameterName = "@CardID",
               .Value = emp.CardID
           })
            cmd.Parameters.Add(New SqlParameter() With {
                .ParameterName = "@BookID",
                .Value = emp.BookID
            })

            cmd.Parameters.Add(New SqlParameter() With {
              .ParameterName = "@IssuedBy",
              .Value = emp.IssuedBy
          })


            con.Open()
            cmd.ExecuteNonQuery()

        End Using
    End Sub
End Class

Answer 1

我建议根据此示例对您的代码进行建模，我修改了您提供的删除子程序，以包含一个带有自定义 ErrorRoutine 的捕获，用于未处理的情况，否则您可以从 executeNonQuery() 函数中获取已删除行的数量。我也改变了，所以我们返回删除的行数，这样如果它小于 1，你可以在调用删除后对消息做任何你想做的事情。

    Public Sub DeleteRecord1(ByVal emp As Details) As Integer

    Dim cs As String = ConfigurationManager.ConnectionStrings("library management 
    systemConnectionString").ConnectionString
    Dim m_RowsDeleted As Integer
    Dim con As SqlConnection = New SqlConnection(cs)

    Try
        Using con
            Dim cmd As SqlCommand = New SqlCommand("spDeleteByID", con)
            cmd.CommandType = CommandType.StoredProcedure
            cmd.Parameters.Add(New SqlParameter() With {
                .ParameterName = "@CardID",
                .Value = emp.CardID
            })

            con.Open()
            m_RowsDeleted = cmd.ExecuteNonQuery()
        End Using
    Catch ex As Exception
        ErrorRoutine(ex, "Delete")
    Finally
        If Not IsNothing(con) Then
            If con.State = ConnectionState.Open Then
                con.Close()
            End If
        End If
    End Try
    Return m_RowsDeleted
End Sub