csharp: LocalDataCache.sync

app.config:

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<?xml version="1.0" encoding="utf-8" ?> <configuration>     <configSections>         <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >             <section name="GBADesktopClient.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />         </sectionGroup>     </configSections>     <connectionStrings>         <add name="GBADesktopClient.Properties.Settings.ServerGBAppraiseDemoConnectionString"             connectionString="Data Source=.;Initial Catalog=GBAppraiseDemo;Persist Security Info=True;User ID=gbauser;Password=gbauser"             providerName="System.Data.SqlClient" />         <add name="GBADesktopClient.Properties.Settings.ClientGBAppraiseDemoConnectionString"             connectionString="Data Source=|DataDirectory|\GBAppraiseDemo.sdf;Max Database Size=2047"             providerName="Microsoft.SqlServerCe.Client.3.5" />     </connectionStrings>     <applicationSettings>         <GBADesktopClient.Properties.Settings>             <setting name="SyncWebServiceURL" serializeAs="String">                 <value>http://yourserver/Service.asmx</value>             </setting>         </GBADesktopClient.Properties.Settings>     </applicationSettings>     <system.serviceModel>         <bindings>             <wsHttpBinding>                 <binding name="WSHttpBinding_IGBACacheSyncContract" closeTimeout="00:01:00"                     openTimeout="00:01:00" receiveTimeout="00:10:00" sendTimeout="00:01:00"                     bypassProxyOnLocal="false" transactionFlow="false" hostNameComparisonMode="StrongWildcard"                     maxBufferPoolSize="524288" maxReceivedMessageSize="65536"                     messageEncoding="Text" textEncoding="utf-8" useDefaultWebProxy="true"                     allowCookies="false">                     <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384"                         maxBytesPerRead="4096" maxNameTableCharCount="16384" />                     <reliableSession ordered="true" inactivityTimeout="00:10:00"                         enabled="false" />                     <security mode="Message">                         <transport clientCredentialType="Windows" proxyCredentialType="None"                             realm="" />                         <message clientCredentialType="Windows" negotiateServiceCredential="true"                             algorithmSuite="Default" establishSecurityContext="true" />                     </security>                 </binding>             </wsHttpBinding>         </bindings>         <client>             <endpoint address="http://localhost:8080/GBACacheSyncService/"                 binding="wsHttpBinding" bindingConfiguration="WSHttpBinding_IGBACacheSyncContract"                 contract="GBAConfiguredSyncWcfService.IGBACacheSyncContract"                 name="WSHttpBinding_IGBACacheSyncContract">             </endpoint>         </client>     </system.serviceModel> </configuration>

　　

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using System; using System.Collections.Generic; using System.Text; using Microsoft.Synchronization.Data; using Microsoft.Synchronization.Data.SqlServerCe; using Microsoft.Synchronization;     namespace GBADeviceClient.Sync {     public class ClientSyncAgent : SyncAgent     {           public ClientSyncAgent()         {             //Hook between SyncAgent and SqlCeClientSyncProvider             this.LocalProvider = new SqlCeClientSyncProvider(Settings.Default.LocalConnectionString, true);                           //Adds the JobList and PropertyDetails tables to the SyncAgent             //setting the SyncDirection to bidirectional             //drop and recreate the table if exists             this.Configuration.SyncTables.Add("JobList");             this.Configuration.SyncTables.Add("PropertyDetails");             this.Configuration.SyncTables["JobList"].SyncDirection = SyncDirection.Bidirectional;             this.Configuration.SyncTables["JobList"].CreationOption = TableCreationOption.DropExistingOrCreateNewTable;             this.Configuration.SyncTables["PropertyDetails"].SyncDirection = SyncDirection.Bidirectional;             this.Configuration.SyncTables["PropertyDetails"].CreationOption = TableCreationOption.DropExistingOrCreateNewTable;                             // The ServerSyncProviderProxy is a type used to abstract the particular transport             // It simply uses reflection to map known method names required by the SyncProvider             // In this case, we hand edited a Web Service proxy             // The web service proxy required editing as VS generates proxies for all types returned by a web servcie             // In this case, we have all the types for Sync Services, and duplicating types will cause errors             this.RemoteProvider =                 new ServerSyncProviderProxy(                     new Sync.ConfiguredSyncWebServiceProxy(Settings.Default.WebServiceURL));         }     } }

　　

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using System; using System.Linq; using System.Collections.Generic; using System.Windows.Forms; using System.Data.SqlServerCe;   namespace GBADeviceClient {       /// <summary>     /// https://www.microsoft.com/zh-cn/download/details.aspx?id=15784  Microsoft Synchronization Services for ADO.NET - 简体中文     /// https://www.microsoft.com/zh-CN/download/details.aspx?id=6497  Microsoft SQL Server Compact 3.5 联机丛书和示例     /// System.Data.SqlServerCe     /// C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Devices     /// 如何：将本地数据库和远程数据库配置为双向同步     /// https://docs.microsoft.com/zh-cn/previous-versions/bb629326%28v%3dvs.110%29     /// https://www.codeproject.com/Articles/22122/Database-local-cache     /// https://docs.microsoft.com/zh-cn/previous-versions/aa983341%28v%3dvs.110%29 SQL Server Compact 4.0 和 Visual Studio     /// https://www.microsoft.com/en-us/download/details.aspx?id=21880 Microsoft SQL Server Compact 4.0 Books Online     /// </summary>     static class Program     {         /// <summary>         /// The main entry point for the application.         /// </summary>         [MTAThread]         static void Main()         {             //Validate the database exists             // If the local database doesn't exist, the app requires initilization             using (SqlCeConnection conn = new SqlCeConnection(Settings.Default.LocalConnectionString))             {                 if (!System.IO.File.Exists(conn.Database))                 {                     DialogResult result = MessageBox.Show(                         "The application requires a first time sync to continue.  Would you like to Sync Now?",                         "Fist Time Run",                         MessageBoxButtons.OKCancel,                         MessageBoxIcon.Exclamation,                         MessageBoxDefaultButton.Button1);                     if (result == DialogResult.OK)                     {                         try                         {                             using (SynchronizingProgress progressForm = new SynchronizingProgress())                             {                                 // Pop a Progress form to get the cursor and provide feedback                                 // on what's happening                                 // The current UI is simply to make sure the wiat cursor shows                                 progressForm.Show();                                 // Make sure the form is displayed                                 Application.DoEvents();                                 Cursor.Current = Cursors.WaitCursor;                                 Cursor.Show();                                 Sync.ClientSyncAgent syncAgent = new Sync.ClientSyncAgent();                                 syncAgent.Synchronize();                             }                         }                         catch (Exception ex)                         {                             // Oooops, something happened                             MessageBox.Show(                                 "Unable to synchronize..." + Environment.NewLine + ex.ToString(),                                 "Error during initial sync",                                 MessageBoxButtons.OK,                                 MessageBoxIcon.Exclamation,                                 MessageBoxDefaultButton.Button1);                         }                         finally                         {                             //Always, always, be sure to reset the cursor                             Cursor.Current = Cursors.Default;                         }                     }                     else                         return;                 } // If database exists             } // Using conn                           // Good to go             Application.Run(new GBAppraiseUI());         }     } }

　　

https://www.codeproject.com/Articles/22122/Database-local-cache

 

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using System; using System.Collections.Generic; using System.Data; using System.Data.SqlClient; using System.Globalization; using System.IO; using System.Reflection; using System.Text.RegularExpressions; using System.Data.Common;   namespace Konamiman.Data {     /// <summary>     /// Represents a local filesystem based cache for binary objects stored in a database https://www.codeproject.com/Articles/22122/Database-local-cache     /// </summary>     /// <remarks>     /// <para>     /// This class allows you to store binary objects in a database table, but using the a local filesystem cache     /// to increase the data retrieval speed when requesting the same data repeatedly.     /// </para>     /// <para>     /// To use the class, you need a table with three columns: a string column for the object name     /// (objects are uniquely identified by their names), a binary column     /// for the object value, and a timestamp column (any column type is ok as long as the column value automatically changes     /// when the value column changes). You need also a directory in the local filesystem. You specify these values     /// in the class constructor, or via class properties.     /// </para>     /// <para>     /// When you first request an object, it is retrieved from the database and stored in the local cache.     /// The next time you request the same object, the timestamps of the cached object and the database object     /// are compared. If they match, the cached file is returned directly. Otherwise, the cached file is updated     /// with the current object value from the database.     /// </para>     /// </remarks>     class DatabaseFileCache     {         #region Fields and properties           //SQL commands used for database access         SqlCommand selectValueCommand;         SqlCommand selectTimestampCommand;         SqlCommand fileExistsCommand;         SqlCommand insertCommand;         SqlCommand getNamesCommand;         SqlCommand deleteCommand;         SqlCommand renameCommand;           //The local cache directory         DirectoryInfo cacheDirectory;           /// <summary>         /// Gets or sets the maximum execution time for SQL commands, in seconds.         /// </summary>         /// <remarks>         /// Default value is 30 seconds. A larger value may be needed when handling very big objects.         /// </remarks>         public int CommandTimeout         {             get { return selectValueCommand.CommandTimeout; }             set             {                 selectValueCommand.CommandTimeout = value;                 selectTimestampCommand.CommandTimeout = value;                 fileExistsCommand.CommandTimeout = value;                 insertCommand.CommandTimeout = value;                 getNamesCommand.CommandTimeout = value;                 deleteCommand.CommandTimeout = value;                 renameCommand.CommandTimeout = value;             }         }           private SqlConnection _Connection;         /// <summary>         /// Gets or sets the connection object for database access.         /// </summary>         public SqlConnection Connection         {             get             {                 return _Connection;             }             set             {                 _Connection=value;                 CreateCommands();             }         }           private string _TableName;         /// <summary>         /// Gets or sets the name of the table that stores the binary objects in the database.         /// </summary>         public string TableName         {             get             {                 return _TableName;             }             set             {                 _TableName=value;                 UpdateCommandTexts();             }         }           private string _CachePath;         /// <summary>         /// Gets or sets the local cache path.         /// </summary>         /// <remarks>         /// <para>If a relative path is specified, it will be combined with the value of the global variable <b>DataDirectory</b>,         /// if it has a value at all. If not, the path will be combined with the application executable path. You can set the DataDirectory         /// variable with this code: <code>AppDomain.CurrentDomain.SetData("DataDirectory", ruta)</code></para>         /// <para>When retrieving the value, the full path is returned, with DataDirectory or the application path appropriately expanded.</para>         /// </remarks>         public string CachePath         {             get             {                 return _CachePath;             }             set             {                 string dataDirectory=(string)AppDomain.CurrentDomain.GetData("DataDirectory");                 if(dataDirectory==null)                     dataDirectory=Path.GetDirectoryName(Assembly.GetEntryAssembly().Location);                 _CachePath=Path.Combine(dataDirectory, value);                 cacheDirectory=new DirectoryInfo(_CachePath);             }         }           private string _NameColumn;         /// <summary>         /// Gets or sets the name of the column for the object name in the database table that stores the binary objects         /// </summary>         /// <remarks>         /// Binary objects are uniquely identified by their names. This column should be defined with a "unique"         /// constraint in the database, but this is not mandatory.         /// </remarks>         public string NameColumn         {             get             {                 return _NameColumn;             }             set             {                 _NameColumn=value;                 UpdateCommandTexts();             }         }           private string _ValueColumn;         /// <summary>         /// Gets or sets the name of the column for the object contents in the database table that stores the binary objects         /// </summary>         /// <remarks>         /// This column may be of any data type that ADO.NET can convert to and from byte arrays.         /// </remarks>         public string ValueColumn         {             get             {                 return _ValueColumn;             }             set             {                 _ValueColumn=value;                 UpdateCommandTexts();             }         }           private string _TimestampColumn;         /// <summary>         /// Gets or sets the name of the column for the timestamp in the database table that stores the binary objects         /// </summary>         /// <remarks>         /// This column may be of any data type that ADO.NET can convert to and from byte arrays.         /// Also, the column value must automatically change when the value column changes.         /// </remarks>         public string TimestampColumn         {             get             {                 return _TimestampColumn;             }             set             {                 _TimestampColumn=value;                 UpdateCommandTexts();             }         }           #endregion           #region Constructors           // Parameterless constructor is declared as private to avoid creating instances with no associated connection object         private DatabaseFileCache() { }           /// <summary>         /// Creates a new instance of the class.         /// </summary>         /// <param name="connection">Connection object for database access.</param>         /// <param name="tableName">Name of the table that stores the binary objects in the database.</param>         /// <param name="cachePath">Local cache path (absolute or relative, see property CachePath).</param>         /// <param name="nameColumn">Name of the column for the object name in the database table that stores the binary objects.</param>         /// <param name="valueColumn">Name of the column for the object contents in the database table that stores the binary objects.</param>         /// <param name="timestampColumn">Name of the column for the timestamp in the database table that stores the binary objects.</param>         public DatabaseFileCache(SqlConnection connection, string tableName, string cachePath, string nameColumn, string valueColumn, string timestampColumn)         {             _TableName=tableName;             CachePath=cachePath;             _NameColumn=nameColumn;             _ValueColumn=valueColumn;             _TimestampColumn=timestampColumn;             Connection=connection;         }           /// <summary>         /// Creates a new instance of the class, assuming the default names <b>Name</b>, <b>Value</b> and <b>timestamp</b> for the names         /// of the columns in the database table that stores the binary objects.         /// </summary>         /// <param name="connection">Connection object for database access.</param>         /// <param name="tableName">Name of the table that stores the binary objects in the database.</param>         /// <param name="cachePath">Local cache path (absolute or relative, see property CachePath).</param>         public DatabaseFileCache(SqlConnection connection, string tableName, string cachePath)             : this(connection, tableName, cachePath, "Name", "Value", "timestamp") { }           /// <summary>         /// Creates a new instance of the class, assuming the default names <b>Name</b>, <b>Value</b> and <b>timestamp</b> for the names.         /// Also, assumes that the table name is <b>Objects</b>, and sets the local cache path to the relative name <b>DatabaseCache</b>         /// (see property CachePath).         /// </summary>         /// <param name="connection">Connection object for database access.</param>         public DatabaseFileCache(SqlConnection connection)             : this(connection, "Objects", "DatabaseCache") { }           #endregion           #region Public methods           /// <summary>         /// Obtains a binary object from the local cache, retrieving it first from the database if necessary.         /// </summary>         /// <remarks>         /// <para>         /// A database connection is first established to check that an object with the specified name actually exists in the database.         /// If not, <b>null</b> is returned.         /// </para>         /// <para>         /// Then the local cache is examinated to see if the object has been already cached. If not, the whole object is         /// retrieved from the database, the cached file is created, and the file path is returned.         /// </para>         /// <para>         /// If the object was already cached, the timestamp of both the database object and the cached file are compared.         /// If they are equal, the cached file path is returned directly. Otherwise, the cached file is recreated         /// from the updated object data in the database.         /// </para>         /// </remarks>         /// <param name="objectName">Name of the object to retrieve.</param>         /// <returns>Full path of the cached file, or <i>null</i> if there is not an object with such name in the database.</returns>         public string GetObject(string objectName)         {             Connection.Open();             try             {                 //* Obtain object timestamp from the database                   selectTimestampCommand.Parameters["@name"].Value=objectName;                 byte[] timestampBytes=(byte[])selectTimestampCommand.ExecuteScalar();                 if(timestampBytes==null)                     return null;    //No object with such name found in the database                   string timestamp="";                 foreach(byte b in timestampBytes)                     timestamp+=b.ToString("X").PadLeft(2, '0');                   //* Checks that the object is cached and that the cached file is up to date                   string escapedFileName=EscapeFilename(objectName);                 FileInfo[] fileInfos=cacheDirectory.GetFiles(EscapeFilename(objectName)+".*");                 if(fileInfos.Length>0)                 {                     string cachedTimestamp=Path.GetExtension(fileInfos[0].Name);                     if(cachedTimestamp==timestamp)                         return fileInfos[0].FullName;   //Up to date cached version exists: return it                     else                         fileInfos[0].Delete();  //Outdated cached version exists: delete it                 }                   //* Object was not cached or cached file was outdated: retrieve it from database and cache it                   string fullLocalFileName=Path.Combine(CachePath, escapedFileName)+"."+timestamp;                 selectValueCommand.Parameters["@name"].Value=objectName;                 File.WriteAllBytes(fullLocalFileName, (byte[])selectValueCommand.ExecuteScalar());                   return fullLocalFileName;             }             finally             {                 Connection.Close();             }         }           /// <summary>         /// Obtains the cached version of a database object, if it exists.         /// </summary>         /// <param name="objectName">Name of the object whose cached version is to be retrieved.</param>         /// <returns>Full path of the cached file, or <i>null</i> if there the specified object is not cached.</returns>         /// <remarks>         /// This method does not access the database at all, it only checks the local cache.         /// It should be used only when the database becomes unreachable, and only if it is acceptable         /// to use data that may be outdated.         /// </remarks>         public string GetCachedFile(string objectName)         {             FileInfo[] fileInfos=cacheDirectory.GetFiles(EscapeFilename(objectName)+".*");             if(fileInfos.Length>0)                 return fileInfos[0].FullName;             else                 return null;         }           /// <summary>         /// Creates or updates a binary object in the database from a byte array.         /// </summary>         /// <param name="value">Contents of the binary object.</param>         /// <param name="objectName">Object name.</param>         /// <remarks>         /// If there is already an object with the specified name in the database, its contents are updated.         /// Otherwise, a new object record is created.         /// </remarks>         public void SaveObject(byte[] value, string objectName)         {             insertCommand.Parameters["@name"].Value=objectName;             insertCommand.Parameters["@value"].Value=value;             Connection.Open();             try             {                 insertCommand.ExecuteNonQuery();             }             finally             {                 Connection.Close();             }         }           /// <summary>         /// Creates or updates a binary object in the database from the contents of a file.         /// </summary>         /// <param name="filePath">Full path of the file containing the object data.</param>         /// <param name="objectName">Object name.</param>         /// <remarks>         /// If there is already an object with the specified name in the database, its contents are updated.         /// Otherwise, a new object record is created.         /// </remarks>         public void SaveObject(string filePath, string objectName)         {             SaveObject(File.ReadAllBytes(filePath), objectName);         }           /// <summary>         /// Creates or updates a binary object in the database from the contents of a file,         /// using the file name (without path) as the object name.         /// </summary>         /// <param name="filePath">Full path of the file containing the object data.</param>         /// <remarks>         /// If there is already an object with the specified name in the database, its contents are updated.         /// Otherwise, a new object record is created.         /// </remarks>         public void SaveObject(string filePath)         {             SaveObject(filePath, Path.GetFileName(filePath));         }           /// <summary>         /// Deletes an object from the database and from the local cache.         /// </summary>         /// <param name="objectName">Object name.</param>         /// <remarks>         /// If the object does not exist in the database, nothing happens and no error is returned.         /// </remarks>         public void DeleteObject(string objectName)         {             //* Delete object from database               deleteCommand.Parameters["@name"].Value=objectName;               Connection.Open();             try             {                 deleteCommand.ExecuteNonQuery();             }             finally             {                 Connection.Close();             }               //* Delete object from local cache               FileInfo[] files=cacheDirectory.GetFiles(EscapeFilename(objectName)+".*");             foreach(FileInfo file in files) file.Delete();         }           /// <summary>         /// Changes the name of an object in the database, and in the local cache.         /// </summary>         /// <param name="oldName">Old object name.</param>         /// <param name="newName">New object name.</param>         /// <remarks>         /// If the object does not exist in the database, nothing happens and no error is returned.         /// </remarks>         public void RenameObject(string oldName, string newName)         {             //* Rename object in database               renameCommand.Parameters["@oldName"].Value=oldName;             renameCommand.Parameters["@newName"].Value=newName;               Connection.Open();             try             {                 renameCommand.ExecuteNonQuery();             }             finally             {                 Connection.Close();             }               //* Rename object in local cache               string escapedOldName=EscapeFilename(oldName);             string escapedNewName=EscapeFilename(newName);               FileInfo[] files=cacheDirectory.GetFiles(escapedOldName+".*");             foreach(FileInfo file in files)             {                 string timestamp=Path.GetExtension(file.Name);                 file.MoveTo(Path.Combine(CachePath, escapedNewName+timestamp));             }         }           /// <summary>         /// Deletes all cached files that have no matching object in the database.         /// </summary>         /// <remarks>         /// Cached files with no matching object in the database could appear if another user         /// (or another application) deletes an object that was already cached.         /// </remarks>         public void PurgeCache()         {             List<string> databaseObjectNames=new List<string>(GetObjectNames());             FileInfo[] files=cacheDirectory.GetFiles();             foreach(FileInfo file in files)             {                 if(!databaseObjectNames.Contains(UnescapeFilename(Path.GetFileNameWithoutExtension(file.Name))))                     file.Delete();             }         }           /// <summary>         /// Checks whether an object exists in the database or not.         /// </summary>         /// <param name="objectName">Object name.</param>         /// <returns><b>True</b> if there is an object with the specified name in the database, <b>False</b> otherwise.</returns>         /// <remarks>         /// The local cache is not accessed, only the database is checked.         /// </remarks>         public bool ObjectExists(string objectName)         {             fileExistsCommand.Parameters["@name"].Value=objectName;             Connection.Open();             try             {                 int exists=(int)fileExistsCommand.ExecuteScalar();                 return exists==1;             }             finally             {                 Connection.Close();             }         }           /// <summary>         /// Obtains the names of all the objects stored in the database.         /// </summary>         /// <returns>Names of all the objects stored in the database.</returns>         /// <remarks>         /// The local cache is not accessed, only the database is checked.         /// </remarks>         public string[] GetObjectNames()         {             List<string> names=new List<string>();             Connection.Open();             try             {                 SqlDataReader reader=getNamesCommand.ExecuteReader();                 while(reader.Read())                 {                     names.Add(reader.GetString(0));                 }                 reader.Close();                 return names.ToArray();             }             finally             {                 Connection.Close();             }         }           #endregion           #region Private methods           /// <summary>         /// Escapes an object name so that it is a valid filename.         /// </summary>         /// <param name="fileName">Original object name.</param>         /// <returns>Escaped name.</returns>         /// <remarks>         /// All characters that are not valid for a filename, plus "%" and ".", are converted into "%uuuu", where uuuu is the hexadecimal         /// unicode representation of the character.         /// </remarks>         private string EscapeFilename(string fileName)         {             char[] invalidChars=Path.GetInvalidFileNameChars();               // Replace "%", then replace all other characters, then replace "."               fileName=fileName.Replace("%", "%0025");             foreach(char invalidChar in invalidChars)             {                 fileName=fileName.Replace(invalidChar.ToString(), string.Format("%{0,4:X}", Convert.ToInt16(invalidChar)).Replace(' ', '0'));             }             return fileName.Replace(".", "%002E");         }           /// <summary>         /// Unescapes an escaped file name so that the original object name is obtained.         /// </summary>         /// <param name="escapedName">Escaped object name (see the EscapeFilename method).</param>         /// <returns>Unescaped (original) object name.</returns>         public string UnescapeFilename(string escapedName)         {             //We need to temporarily replace %0025 with %! to prevent a name             //originally containing escaped sequences to be unescaped incorrectly             //(for example: ".%002E" once escaped is "%002E%0025002E".             //If we don't do this temporary replace, it would be unescaped to "..")               string unescapedName=escapedName.Replace("%0025", "%!");             Regex regex=new Regex("%(?<esc>[0-9A-Fa-f]{4})");             Match m=regex.Match(escapedName);             while(m.Success)             {                 foreach(Capture cap in m.Groups["esc"].Captures)                     unescapedName=unescapedName.Replace("%"+cap.Value, Convert.ToChar(int.Parse(cap.Value, NumberStyles.HexNumber)).ToString());                 m=m.NextMatch();             }             return unescapedName.Replace("%!", "%");         }           /// <summary>         /// Creates the commands for database access.         /// </summary>         /// <remarks>         /// This method is executed when the Connection property changes.         /// </remarks>         private void CreateCommands()         {             selectValueCommand=Connection.CreateCommand();             selectValueCommand.Parameters.Add("@name", SqlDbType.NVarChar);             selectTimestampCommand=Connection.CreateCommand();             selectTimestampCommand.Parameters.Add("@name", SqlDbType.NVarChar);             fileExistsCommand=Connection.CreateCommand();             fileExistsCommand.Parameters.Add("@name", SqlDbType.NVarChar);             insertCommand=Connection.CreateCommand();             insertCommand.Parameters.Add("@name", SqlDbType.NVarChar);             insertCommand.Parameters.Add("@value", SqlDbType.VarBinary);             getNamesCommand=Connection.CreateCommand();             deleteCommand=Connection.CreateCommand();             deleteCommand.Parameters.Add("@name", SqlDbType.NVarChar);             renameCommand=Connection.CreateCommand();             renameCommand.Parameters.Add("@oldName", SqlDbType.NVarChar);             renameCommand.Parameters.Add("@newName", SqlDbType.NVarChar);               UpdateCommandTexts();         }           /// <summary>         /// Updates the text of the commands used for database access.         /// </summary>         /// <remarks>         /// This method is executed when any of these properties change: TableName, NameColumn, ValueColumn, TimestampColumn.         /// </remarks>         private void UpdateCommandTexts()         {             selectValueCommand.CommandText=string.Format(                 "select {0} from {1} where {2}=@name", ValueColumn, TableName, NameColumn);               selectTimestampCommand.CommandText=string.Format(                 "select {0} from {1} where {2}=@name", TimestampColumn, TableName, NameColumn);               fileExistsCommand.CommandText=string.Format(                 "if exists(select {0} from {1} where {0}=@name) select 1; else select 0;", NameColumn, TableName);               insertCommand.CommandText=string.Format(                 "if exists (select {0} from {1} where {0}=@name) update {1} set {2}=@value where {0}=@name; else insert into {1} ({0}, {2}) values (@name, @value);",                 NameColumn, TableName, ValueColumn);               getNamesCommand.CommandText=string.Format("select {0} from {1}", NameColumn, TableName);               deleteCommand.CommandText=string.Format(                 "delete from {0} where {1}=@name", TableName, NameColumn);               renameCommand.CommandText=string.Format(                 "update {0} set {1}=@newName where {1}=@oldName", TableName, NameColumn);         }           #endregion     } }