Question

我有以下代码;

  Dim rdr As SqlCeDataReader = cm_sel.ExecuteReader
  If rdr.HasRows Then
    While rdr.Read
      Documents.DeleteDocument(rdr.Item("fID"))
    End While
  End If

我得到的错误是：

如果是，SQL Server Compact不支持对HasRows属性的调用底层游标不可滚动。

那么在实际读取DataReader之前我应该如何检查数据是否存在？

修改

整个代码：

 Dim con As New SqlCeConnection(ConfigurationManager.ConnectionStrings("MyConnectionString").ToString)
 Dim cm_sel As New SqlCeCommand("SELECT fID FROM Files WHERE fCatID=" & catID, con)
   Try
     con.Open()
     Dim rdr As SqlCeDataReader = cm_sel.ExecuteReader

      If rdr.HasRows() Then
         While rdr.Read
            Documents.DeleteDocument(rdr.Item("fID"))
          End While
       End If

        Return "{'result':'ok'}"
     Catch ex As Exception
         Return "{'result':'error'}"
      Finally
          con.Close()
          con.Dispose()
      End Try

Answer 1

您可以直接调用reader.Read，因为如果没有行，则返回false。只需删除if周围的while声明。

更新代码：

Dim rdr As SqlCeDataReader = cm_sel.ExecuteReader
    While rdr.Read
      Documents.DeleteDocument(rdr.Item("fID"))
    End While

Answer 2

这适用于上述问题。

 Dim hasrows As Boolean
 hasrows = False
 While (rdr.Read())
   hasrows = True
 End While
 If (hasrows) Then
  --do something
else
--do something else
end if

If you assign hasrows function to any Boolean and try to use it, the reader can jump to second record. The above solution will avoid that scenario as well.

SQL Server CE不支持DataReader.HasRows？

2 个答案: