如何：保存和还原更改令牌
上次修改时间： 2009年7月28日
适用范围： SharePoint Foundation 2010
如果应用程序定期查询更改日志，您可能需要保留运行结束时的最后一个更改令牌，并在以后重新构造所保留的令牌，以将其作为下一次运行的起点。若要保存更改令牌，请首先调用 SPChangeToken.ToString() 方法以获取该令牌的字符串表示；然后将结果保存到永久存储中。若要还原令牌，请从存储中检索该字符串，然后将其传递给 SPChangeToken.SPChangeToken(String) 构造函数。
.gif "警告注释") 警告 |
|---|
更改令牌特定于列表、网站、网站集或内容数据库。不能将来自某个对象的 SPChangeToken 对象用在另一个对象的 GetChanges 方法中。此规则的唯一例外是：在内容数据库中包含的任何对象的 GetChanges 方法中可以使用来自 SPContentDatabase 对象的 SPChangeToken 对象。 |
示例
下面的示例是一个控制台应用程序，用于查询有关内容数据库范围更改的更改日志。
应用程序首次运行时，查询会检索从日志开头到当前结束位置记录的所有更改。此查询的执行过程是：先将 SPChangeQuery 对象的 ChangeTokenStart 属性设置为空值，然后将 SPQuery 对象传递给 GetChanges 方法。处理完所有更改后，该程序会通过调用 ToString() 方法将最后一批更改的最后一个更改令牌序列化，并将结果存储在磁盘上的文件中。
在后续的运行中，程序会反序列化所存储的更改令牌，并使用它来设置 ChangeTokenStart 属性，该属性针对更改日志定义查询的起点。ChangeTokenEnd 属性则保留为默认的空值，这表示查询应继续执行到日志的末尾。
重要的工作是通过 GetStartingToken 函数完成的，即，在这里调用 SPChangeToken 构造函数。
using System;
using System.IO;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Administration;
namespace Test
{
class ConsoleApp
{
private const string DATA_FILE_PATH = "ChangeToken.dat";
static void Main(string[] args)
{
using (SPSite site = new SPSite("https://localhost"))
{
SPChangeQuery query = new SPChangeQuery(true, true);
query.ChangeTokenStart = GetStartingToken();
while (true)
{
// Get a batch of changes.
SPChangeCollection changes = site.ContentDatabase.GetChanges(query);
// Process them.
foreach (SPChange change in changes)
{
Console.WriteLine("Date: {0} Type of object: {1} Type of change: {2}",
change.Time.ToShortDateString(), change.GetType().ToString(), change.ChangeType);
}
// Starting point for next batch.
query.ChangeTokenStart = changes.LastChangeToken;
// If this is the last batch, exit.
if (changes.Count < query.FetchLimit)
break;
}
// Serialize the last token as a starting point for the next run.
SaveLastToken(query.ChangeTokenStart);
}
Console.Write("\nPress ENTER to continue...");
Console.ReadLine();
}
static SPChangeToken GetStartingToken()
{
// Passing a null token to GetChanges fetches
// changes from the start of the log.
SPChangeToken token = null;
// If we have a token from the last run, use it.
if (File.Exists(DATA_FILE_PATH))
{
using (FileStream fs = File.OpenRead(DATA_FILE_PATH))
{
BinaryReader br = new BinaryReader(fs);
try
{
string str = br.ReadString();
// Construct a change token from serialized string.
token = new SPChangeToken(str);
}
catch (EndOfStreamException e)
{
// No serialized string, so do nothing.
}
finally
{
br.Close();
}
}
}
return token;
}
static void SaveLastToken(SPChangeToken token)
{
using (FileStream fs = File.Create(DATA_FILE_PATH))
{
// Serialize the token.
BinaryWriter bw = new BinaryWriter(fs);
string s = token.ToString();
bw.Write(s);
// Flush and close.
bw.Flush();
bw.Close();
}
}
}
}
Imports System
Imports System.IO
Imports Microsoft.SharePoint
Imports Microsoft.SharePoint.Administration
Module ConsoleApp
Private Const DATA_FILE_PATH As String = "ChangeToken.dat"
Sub Main()
Using site As SPSite = New SPSite("https://localhost")
Dim query As New SPChangeQuery(True, True)
query.ChangeTokenStart = GetStartingToken()
While (True)
' Get a batch of changes.
Dim changes As SPChangeCollection = site.ContentDatabase.GetChanges(query)
' Process them.
For Each change As SPChange In changes
Console.WriteLine("Date: {0} Type of object: {1} Type of change: {2}", _
change.Time.ToShortDateString(), change.GetType().ToString(), change.ChangeType)
Next
' This is the starting point for next batch.
query.ChangeTokenStart = changes.LastChangeToken
' If this is the last batch, exit.
If changes.Count < query.FetchLimit Then
Exit While
End If
End While
' Serialize the last token as a starting point for the next run.
SaveLastToken(query.ChangeTokenStart)
End Using
Console.Write(vbCrLf + "Press ENTER to continue...")
Console.ReadLine()
End Sub
Function GetStartingToken() As SPChangeToken
' Passing a null token to GetChanges fetches
' changes from the start of the log.
Dim token As SPChangeToken = Nothing
' If we have a token from the last run, use it.
If File.Exists(DATA_FILE_PATH) Then
Using fs As FileStream = File.OpenRead(DATA_FILE_PATH)
Dim br As BinaryReader = New BinaryReader(fs)
Try
Dim str As String = br.ReadString()
' Construct a change token from serialized string.
token = New SPChangeToken(str)
Catch e As EndOfStreamException
' No serialized string, so do nothing.
Finally
br.Close()
End Try
End Using
End If
Return token
End Function
Sub SaveLastToken(ByRef token As SPChangeToken)
Using fs As FileStream = File.Create(DATA_FILE_PATH)
' Serialize the token.
Dim bw As BinaryWriter = New BinaryWriter(fs)
Dim s As String = token.ToString()
bw.Write(s)
' Flush and close.
bw.Flush()
bw.Close()
End Using
End Sub
End Module