微软(以及许多开发人员)声称 SqlDataReader.GetOrdinal 方法比使用命名查找,例如 reader["ColumnName"],提高了从 DataReader 检索值的性能。问题是在处理小型分页记录集时,真正的性能差异是什么?是否值得在代码中寻找和引用序数索引所带来的额外开销?
微软(以及许多开发人员)声称 SqlDataReader.GetOrdinal 方法比使用命名查找,例如 reader["ColumnName"],提高了从 DataReader 检索值的性能。问题是在处理小型分页记录集时,真正的性能差异是什么?是否值得在代码中寻找和引用序数索引所带来的额外开销?
这包括使用字符串索引器进行的间接调用。
您可以在循环顶部使用GetOrdinal将序数放入数组中,并使数组中的索引为const或具有枚举(根本不需要GetOrdinal),或者使用GetOrdinal转换为具有描述性名称的单个变量。
只有当数据集很小的时候,我才会真正考虑这种过早的优化。
是和不是。
如果你正在处理大量数据,使用序数而不是列名肯定会对你有所帮助。
否则,保持简单、可读和相对安全 - 使用列名即可。
只有在需要时才进行优化。
int ordinalUserName = reader.GetOrdinal("user_name")
,这样也更容易阅读。如果你在一个地方声明所有的序数而不是将列名散布在某些逻辑中,那么它也可以被认为是更易读和更安全的。 - row1Friend Class DataReader
Implements IDisposable
Private _reader As SqlDataReader
Private _oridinals As Dictionary(Of String, Integer)
Private Shared _stringComparer As StringComparer = StringComparer.OrdinalIgnoreCase 'Case in-sensitive
Public Sub New(reader As SqlDataReader)
Me._reader = reader
Me.SetOrdinals()
End Sub
Private Sub SetOrdinals()
Me._oridinals = New Dictionary(Of String, Integer)(_stringComparer)
For i As Integer = 0 To Me._reader.FieldCount - 1
Me._oridinals.Add(Me._reader.GetName(i), i)
Next
End Sub
Public Function Read() As Boolean
Return Me._reader.Read()
End Function
Public Function NextResult() As Boolean
Dim value = Me._reader.NextResult()
If value Then
Me.SetOrdinals()
End If
Return value
End Function
Default Public ReadOnly Property Item(name As String) As Object
Get
Return Me._reader(Me.GetOrdinal(name))
End Get
End Property
Public Function GetOrdinal(name As String) As Integer
Return Me._oridinals.Item(name)
End Function
Public Function GetInteger(name As String) As Integer
Return Me._reader.GetInt32(Me.GetOrdinal(name))
End Function
Public Function GetString(ordinal As Integer) As String
Return Me._reader.GetString(ordinal)
End Function
Public Function GetString(name As String) As String
Return Me._reader.GetString(Me.GetOrdinal(name))
End Function
Public Function GetDate(name As String) As Date
Return Me._reader.GetDateTime(Me.GetOrdinal(name))
End Function
Public Function GetDateNullable(name As String) As Nullable(Of Date)
Dim o = Me._reader.GetValue(Me.GetOrdinal(name))
If o Is System.DBNull.Value Then
Return Nothing
Else
Return CDate(o)
End If
End Function
Public Function GetDecimal(name As String) As Decimal
Return Me._reader.GetDecimal(Me.GetOrdinal(name))
End Function
Public Function GetBoolean(name As String) As Boolean
Return Me._reader.GetBoolean(Me.GetOrdinal(name))
End Function
Public Function GetByteArray(name As String) As Byte()
Return CType(Me._reader.GetValue(Me.GetOrdinal(name)), Byte())
End Function
Public Function GetBooleanFromYesNo(name As String) As Boolean
Return Me._reader.GetString(Me.GetOrdinal(name)) = "Y"
End Function
'Disposable Code
End Class