未为类型“DBNull"和类型“整数"定义运算符“=" [英] Operator '=' is not defined for type 'DBNull' and type 'Integer'

问题描述

过去几个小时我一直在挣扎，但仍然无法理解这一点.我遇到的问题是，当有人被承认数据库更新给他们 BedID 时，当我尝试释放他们时，我似乎无法将 BedID(在数据库中)设置为 nothing .这是一个问题，因为我需要能够接纳和释放尽可能多的人.

I've been struggling for the past few hours and still can't get my head round this one . The issue I am having is when someone has been admitted the database updates giving them BedID , when I then try and discharge them I can't seem to set the BedID (In the database) to nothing . This is an issue as I need to be able to admit and discharge as many people as I can.

Sub Dis1_Click(ByVal s As Object, ByVal e As EventArgs) Handles Dis1.ServerClick

    Dim time As String = Now().ToString("dd-MM-yyyy hh:mm:ss")

    sql = "UPDATE Allocation  SET BedID = NULL , DischargeDate =" + "'" + time + "'" + " WHERE BedID = 1 "
    cmd = New OdbcCommand(sql, cn)
    cmd.ExecuteNonQuery()
End Sub

Sub BedCheck1()
    If r("BedID") = "" Then
    Else
        If r("BedID") = 1 Then
            ba = s & "<tr><td>" & r("Surname") & "</td>" & "<td>" & r("Forename") & "/<td>" & "<td>" & r("AdmitDate") & "</td>" & "<td>" & r("DischargeDate") & "</td>" & "<td>" & r("comments") & "</td></tr>"
        End If
    End If
End Sub

谢谢！

推荐答案

在读取值之前需要做一个 DbNull-check:

You need to do a DbNull-check before you read the value:

If Not IsDbNull(r("BedID")) Then

    If r("BedID") = "" Then
    Else If r("BedID") = 1 Then
        ba = s & "<tr><td>" & r("Surname") & "</td>" & "<td>" & r("Forename") & "/<td>" & "<td>" & r("AdmitDate") & "</td>" & "<td>" & r("DischargeDate") & "</td>" & "<td>" & r("comments") & "</td></tr>"
    End If
End If

请注意，DbNull 是一种特殊情况，您需要使用 IsDbNull 函数来防止此错误

Note that DbNull is a special case and you need to use the IsDbNull-function to prevent this error

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