步驟 3：重複使用元件

目標

在此步驟中，您將瞭解下列各項：

• 可重複使用的元件。
• 如何規劃重複使用性。

描述

此 COM+ 服務入門的前兩個部分步驟 1：建立交易元件 和 步驟 2：跨多個元件 擴充交易會示範如何撰寫一個元件來呼叫第二個元件，以協助完成某些工作，更新 Microsoft SQL Server Pubs 資料庫中的作者資訊;所有工作都會受到單一交易的保護。 範例元件著重於更新作者數據和驗證作者位址的工作，以及 COM+ 提供的事務處理、 JIT 啟用和 並行保護。

此步驟示範如何重複使用步驟 1 和 2 中建立的元件，並查看這些元件的設計的意義。 如下圖所示，這表示建立新的元件 ， AddNewAuthor藉由呼叫 UpdateAuthorAddress，將新的作者新增至資料庫。

除了重複使用現有的元件功能之外， AddNewAuthor 還呼叫另 ValidateAuthorName一個名為 的新元件。 如上圖所示， ValidateAuthorName 為非交易式。 此元件的交易屬性值會保留在其預設設定 （不支援） 以從交易中排除其工作。 如步驟 3 範例程式代碼所示， ValidateAuthorName 對資料庫執行只讀查詢，而且這個次要工作的失敗不應該有中止交易的可能性。 不過，元件的異動屬性值 AddNewAuthor 會設定為 [必要]。

AddNewAuthor、 UpdateAuthorAddress和 ValidateAuthorAddress 元件都會在交易中投票。 在此交易中， AddNewAuthor 是根物件。 COM+ 一律會在交易中建立第一個物件做為根物件。

在此範例中，重複使用 UpdateAuthorAddress 元件很簡單—COM+ 會自動傳遞預期的服務。 不過，如果元件的交易屬性值 UpdateAuthorAddress 一開始設定 為 [需要新增 ]，而不是 [必要]，則結果會有所不同。 在介面上，這兩個設定看起來都類似;兩者都保證交易。 不過，需要 New 一律會啟動新的交易，而 Required 只有在物件的呼叫端為非交易時才會啟動新的交易。 您可以從中看出，要 UpdateAuthorAddress 謹慎且深思熟慮地進行設定是多麼重要。 否則，COM+ 可能會以不同的方式解譯服務要求，併產生兩個不相關的交易，如下圖所示，而不是一個。

範例指令碼

AddNewAuthor 元件會藉由允許物件保持作用中，以執行新作者的批次新增作業，直到客戶端釋放對對象的參考為止。

Option Explicit
'
'   Purpose:   This class is used for adding a new author.
'
'   Notes:    IMPT:  This component implicitly assumes that it will
'             always run in a transaction. Undefined results may 
'             otherwise occur.
'
'  AddNewAuthor
'
Public Sub AddNewAuthor( _
                        ByVal strAuthorFirstName As String, _
                        ByVal strAuthorLastName As String, _
                        ByVal strPhone As String, _
                        ByVal strAddress As String, _
                        ByVal strCity As String, _
                        ByVal strState As String, _
                        ByVal strZip As String, _
                        ByVal boolContracted As Boolean)
  ' Handle any errors.
  On Error GoTo UnexpectedError

  ' Verify component is in a transaction.
  ' The VerifyInTxn subroutine is described in Step 1.
  VerifyInTxn

  ' Get our object context.
  Dim objcontext As COMSVCSLib.ObjectContext
  Set objcontext = GetObjectContext

  ' Get the IContextState object.
  Dim contextstate As COMSVCSLib.IContextState
  Set contextstate = objcontext

  ' Validate that the author is OK.
  ' The ValidateAuthorName function is described after this function.
  Dim oValidateAuthName As Object
  Dim bValidAuthor As Boolean
  Set oValidateAuthName = CreateObject("ComplusPrimer.ValidateAuthorName")
  bValidAuthor = oValidateAuthName.ValidateAuthorName( _
    strAuthorFirstName, strAuthorLastName)
  If Not bValidAuthor Then
    Err.Raise 999999, "The AddNewAuthor component", _
      "You tried to add an author on the banned list!"
  End If
  
  ' Open the connection to the database.
  Dim conn As ADODB.Connection
  Set conn = CreateObject("ADODB.Connection")

  ' Specify the OLE DB provider.
  conn.Provider = "SQLOLEDB"

  ' Connect using Windows Authentication.
  Dim strProv As String
  strProv = "Server=MyDBServer;Database=pubs;Trusted_Connection=yes"

  ' Open the database.
  conn.Open strProv

  ' Tell the database to actually add the author; use empty strings 
  ' for this part and rely on the UpdateAuthorAddress 
  ' component to validate the address/phone/etc data.
  ' Default Contract flag is off.
  Dim strUpdateString As String
  strUpdateString = "insert into authors values(_
                     '789-65-1234'," & _
                     strAuthorLastName & ", " & _
                     strAuthorFirstName & ", " & _
                     "'(555) 555-5555', ', ', ', '98765', "

  If boolContracted Then
    strUpdateString = strUpdateString + "1)"
  Else
    strUpdateString = strUpdateString + "0)"
  End If

  conn.Execute strUpdateString
  
  ' Close the connection; this potentially allows 
  ' another component in the same transaction to
  ' reuse the connection from the connection pool.
  conn.Close
  Set conn = Nothing
  
  ' Create the UpdateAuthorAddress component.
  Dim oUpdateAuthAddr As Object
  Set oUpdateAuthAddr = CreateObject("ComplusPrimer.UpdateAuthorAddress")
  
  ' The component throws an error if anything goes wrong.
  oUpdateAuthAddr.UpdateAuthorAddress "", strPhone, _
    strAddress, strCity, strState, strZip
    
  Set oUpdateAuthAddr = Nothing
  
  ' Everything works--commit the transaction.
  contextstate.SetMyTransactionVote TxCommit
  
  '  Design issue:  Allow batch additions of new
  '  authors in one transaction, or should each new author be added
  '  in a single new transaction?
  contextstate.SetDeactivateOnReturn False
  Exit Sub
  
UnexpectedError:
  ' There's an error.
  contextstate.SetMyTransactionVote TxAbort
  contextstate.SetDeactivateOnReturn True
  
End Sub

元件會在 ValidateAuthorName 將名稱新增至資料庫之前 AddNewAuthor ，先驗證作者名稱。 如果發生非預期的情況，此元件會將錯誤擲回給其呼叫端。

Option Explicit
'
'   Purpose:   This class is used for validating authors before
'              adding them to the database.
'
'   Notes:   This component doesn't need to be in a transaction because
'            it is performing read-only queries on the database,
'            especially since these queries are not overlapping with
'            any updates of end-user data. If an unexpected error
'            happens, let the error go back to the caller who
'            needs to handle it.
'

Public Function ValidateAuthorName( _
                        ByVal strAuthorFirstName As String, _
                        ByVal strAuthorLastName As String _
                        ) As Boolean
  ValidateAuthorName = False

  ' Open the connection to the database.
  Dim conn As ADODB.Connection
  Set conn = CreateObject("ADODB.Connection")

  ' Specify the OLE DB provider.
  conn.Provider = "SQLOLEDB"

  ' Connect using Windows Authentication.
  Dim strProv As String
  strProv = "Server=MyDBServer;Database=pubs;Trusted_Connection=yes"

  ' Open the database.
  conn.Open strProv

  ' Suppose another hypothetical table has been added to the Pubs 
  ' database, one that contains a list of banned authors.
  Dim rs As ADODB.Recordset
  Set rs = conn.Execute("select * from banned_authors")
  
  ' Loop through the banned-author list looking for the specified
  ' author.
  While Not rs.EOF
    If rs.Fields("FirstName") = strAuthorFirstName And _
      rs.Fields("LastName") = strAuthorLastName Then
        ' This is a banned author.
        conn.Close
        Set conn = Nothing
        Set rs = Nothing
        Exit Function
    End If
    rs.MoveNext
  Wend
  
  ' None of the added authors found in the banned list.
  ValidateAuthorName = True
  conn.Close
  Set conn = Nothing
  Set rs = Nothing
End Function

摘要

• 有時候，您不希望元件在交易中投票。
• COM+ 不會在非交易元件上強制執行 JIT 啟用或並行保護。 您可以個別設定這些服務。
• 呼叫元件的元件的元件會影響 COM+ 如何解譯所呼叫元件的服務要求。

相關主題

步驟 1：建立交易式元件

步驟 2：跨多個元件擴充交易

設定交易

設計延展性