使用ADO.Net时，每次数据库操作都要设置connection属性、建立connection、使用command、事务处理等，比较繁琐，有很多重复工作。能不能把这些繁琐的、常用的操作再封装一下，以更方便、安全地使用。下面这个类就是一种尝试：
using System;
using System.Data.SqlClient;
using System.Text;
using System.Data;
using System.Collections;
using System.Configuration;

public class DBAccess
{
/// <summary>
/// Declare the ole db required objects
/// </summary>

/// <summary>
/// An ole db adapter to act as the bridge to the database
/// </summary>
private SqlDataAdapter dbDataAdapter;
/// <summary>
/// The connection to the database
/// </summary>
private SqlConnection dbConnection;
/// <summary>
/// The command for doing the inserts
/// </summary>
private SqlCommand dbInsertCommand;
/// <summary>
/// The command for doing the deletes
/// </summary>
private SqlCommand dbDeleteCommand;
/// <summary>
/// The command for doing the updates
/// </summary>
private SqlCommand dbUpdateCommand;
/// <summary>
/// The command for doing the Selects
/// </summary>
private SqlCommand dbSelectCommand;

private SqlCommand dbSelectCommandofAdapter;

/// <summary>
/// The command for get dataset
/// </summary>
private SqlDataAdapter dataAdapterCommand;

/// <summary>
/// The data reader for the application
/// </summary>
public SqlDataReader dbDataReader;

/// <summary>
/// Declare an enum to allow internal tracking of commands
/// </summary>
enum COMMAND{ NONE, INSERT, UPDATE, DELETE, SELECT,DATASET };

/// <summary>
/// Internal member for tracking command progress
/// </summary>
private COMMAND command;

/// <summary>
/// String to hold error messages if a command fails
/// </summary>
private string error;

/// <summary>
/// Get a stored error message if ExecuteCommand fails
/// </summary>
public string ErrorMessage
{
get
{
return error;
}
}

/// <summary>
/// bool holder for is open
/// </summary>
private bool bOpen;

/// <summary>
/// Check to see if a data base is open
/// </summary>
public bool IsOpen
{
get
{
return bOpen;
}
}

/// <summary>
/// Declare a string object for the insert command
/// </summary>
public string InsertCommand
{
get
{
return dbInsertCommand.CommandText;
}
set
{
command = COMMAND.INSERT;
dbInsertCommand.CommandText = value;
}
}

/// <summary>
/// Declare a string object for the delete command
/// </summary>
public string DeleteCommand
{
get
{
return dbDeleteCommand.CommandText;
}
set
{
command = COMMAND.DELETE;
dbDeleteCommand.CommandText = value;
}
}

/// <summary>
/// Declare a string object for the update command
/// </summary>
public string UpdateCommand
{
get
{
return dbUpdateCommand.CommandText;
}
set
{
command = COMMAND.UPDATE;
dbUpdateCommand.CommandText = value;
}
}

public string SelectDataSetCommand
{
get
{
return dataAdapterCommand.SelectCommand.CommandText;
}
set
{
command = COMMAND.DATASET;
dataAdapterCommand.SelectCommand.CommandText = value;
}
}

/// <summary>
/// Get the reader from the class
/// </summary>
public SqlDataReader GetReader
{
get
{
switch( command )
{
case COMMAND.NONE: return null;
case COMMAND.DELETE: return DeleteReader;
case COMMAND.INSERT: return InsertReader;
case COMMAND.SELECT: return SelectReader;
case COMMAND.UPDATE: return UpdateReader;
default: return null;
}
}
}

public DataSet GetDataSet
{
get
{
switch( command )
{
case COMMAND.DATASET: return SelectDataSet();
default: return null;
}
}
}

public DataSet SelectDataSet()
{
try
{
dataAdapterCommand.SelectCommand.Connection = dbConnection;
DataSet dataset = new DataSet();
dataAdapterCommand.Fill(dataset);
return dataset;
}
catch (Exception exp)
{
error = exp.Message;
return null;
}

}

/// <summary>
/// Execute the command that has been set up previously
/// </summary>
/// <returns>A boolean value indicating true or false</returns>
public bool ExecuteCommand()
{
bool bReturn = false;
if( command == COMMAND.NONE )
{
return bReturn;
}
else if( command == COMMAND.SELECT )
{
/// select only returns true as the get reader function will
/// execute the command

try
{
if( dbDataReader != null )
{
dbDataReader.Close();
dbDataReader = null;
}

bReturn = true;
/// return bReturn;
}
catch( SqlException exp )
{
error = "dbException thrown when trying to Select, error given = " + exp.Message + " check the sql";
return bReturn = false;
}

}
else if( command == COMMAND.DATASET )
{
return bReturn;
}
else
{
int nAffected = -1;

if( dbDataReader != null )
{
dbDataReader.Close();
dbDataReader = null;
}

/// get the transaction object from the connection
SqlTransaction trans = dbConnection.BeginTransaction();

try
{
/// create a nested transaction on the connection transaction
switch( command )
{
case COMMAND.DELETE: dbDeleteCommand.Transaction = trans; break;
case COMMAND.INSERT: dbInsertCommand.Transaction = trans; break;
case COMMAND.UPDATE: dbUpdateCommand.Transaction = trans; break;
}

/// execute the command
switch( command )
{
case COMMAND.DELETE: nAffected = dbDeleteCommand.ExecuteNonQuery(); break;
case COMMAND.INSERT: nAffected = dbInsertCommand.ExecuteNonQuery(); break;
case COMMAND.UPDATE: nAffected = dbUpdateCommand.ExecuteNonQuery(); break;
}

}
catch( InvalidOperationException ioexp )
{
StringBuilder buildError = new StringBuilder();
buildError.Append( "InvalidOperationException thrown when trying to " );

switch( command )
{
case COMMAND.DELETE: buildError.Append( "Delete" ); break;
case COMMAND.INSERT: buildError.Append( "Insert" ); break;
case COMMAND.UPDATE: buildError.Append( "Update" ); break;
}

buildError.Append( ", error given = " + ioexp.Message + " check the sql" );

error = buildError.ToString();

return bReturn = false;
}
catch( SqlException dbexp )
{
StringBuilder buildError = new StringBuilder();
buildError.Append( "InvalidOperationException thrown when trying to " );

switch( command )
{
case COMMAND.DELETE: buildError.Append( "Delete" ); break;
case COMMAND.INSERT: buildError.Append( "Insert" ); break;
case COMMAND.UPDATE: buildError.Append( "Update" ); break;
}

buildError.Append( ", error given = " + dbexp.Message + " check the sql" );

error = buildError.ToString();

return bReturn = false;
}
finally
{
/// commit the command
if( nAffected == 1 )
{
switch( command )
{
case COMMAND.DELETE: dbDeleteCommand.Transaction.Commit(); break;
case COMMAND.INSERT: dbInsertCommand.Transaction.Commit(); break;
case COMMAND.UPDATE: dbUpdateCommand.Transaction.Commit(); break;
}

//trans.Commit();

//trans.Rollback();

bReturn = false;
}
}
}

return bReturn;
}

#region select functions

/// <summary>
/// Get the Select reader from the select command
/// </summary>
private SqlDataReader SelectReader
{
get
{
if( dbDataReader != null )
{
if( dbDataReader.IsClosed == false )
{
dbDataReader.Close();
dbDataReader = null;
}
}

dbDataReader = dbSelectCommand.ExecuteReader();
return dbDataReader;
}
}

/// <summary>
/// Get the Update reader from the update command
/// </summary>
private SqlDataReader UpdateReader
{
get
{
if( dbDataReader.IsClosed == false )
dbDataReader.Close();

dbDataReader = dbSelectCommand.ExecuteReader();
return dbDataReader;
}
}

/// <summary>
/// Get the Insert Reader from the Insert Command
/// </summary>
private SqlDataReader InsertReader
{
get
{
if( dbDataReader.IsClosed == false )
dbDataReader.Close();

dbDataReader = dbSelectCommand.ExecuteReader();
return dbDataReader;
}
}

/// <summary>
/// Get the Delete Reader from the Delete Command
/// </summary>
private SqlDataReader DeleteReader
{
get
{
if( dbDataReader != null )
{
if( dbDataReader.IsClosed == false )
{
dbDataReader.Close();
dbDataReader = null;
}
}

dbDataReader = dbSelectCommand.ExecuteReader();
return dbDataReader;
}
}

#endregion

/// <summary>
/// Standard Constructor
/// </summary>
public DBAccess()
{
/// NOTE That we are not setting the commands up the way the wizard would
/// but building them more generically

// create the command variables
dbDataAdapter = new SqlDataAdapter();
dbConnection = new SqlConnection();
dbSelectCommand = new SqlCommand();
dbDeleteCommand = new SqlCommand();
dbUpdateCommand = new SqlCommand();
dbInsertCommand = new SqlCommand();

/// set up the adapter
dbDataAdapter.DeleteCommand = dbDeleteCommand;
dbDataAdapter.InsertCommand = dbInsertCommand;
dbDataAdapter.SelectCommand = dbSelectCommand;
dbDataAdapter.UpdateCommand = dbUpdateCommand;

/// make sure everyone knows what conection to use
dbSelectCommand.Connection = dbConnection;
dbDeleteCommand.Connection = dbConnection;
dbUpdateCommand.Connection = dbConnection;
dbInsertCommand.Connection = dbConnection;

command = COMMAND.NONE;
dbDataReader = null;

dbSelectCommandofAdapter = new SqlCommand();
dataAdapterCommand = new SqlDataAdapter();
dataAdapterCommand.SelectCommand = dbSelectCommandofAdapter;
}

public void Open()
{
/// set up the connection string
StringBuilder strBuild = new StringBuilder();

//Connection的属性从配置文件读取
strBuild.AppendFormat(ConfigurationSettings.AppSettings["DBConnection"]);

dbConnection.ConnectionString = strBuild.ToString();

try
{
dbConnection.Open();
bOpen = true;
}
catch (Exception exp)
{
error = exp.Message;
}

}

/// <summary>
/// Close the currently open connection
/// </summary>
public void Close()
{
if (dbDataReader != null)
{
if( dbDataReader.IsClosed == false )
{
dbDataReader.Close();
dbDataReader = null;
}
}

dbConnection.Close();
}

}

使用示例：

Insert操作，新建用户：

public bool NewUser()
{
DBAccess newUserDBAccess = new DBAccess();
StringBuilder sqlStr = new StringBuilder();
sqlStr.Append( "Insert into userTable(usrName,pwd,name,depart,role,available) values(");
sqlStr.Append( "'" + usrName + "',");
sqlStr.Append( "'" + pwd + "',");
sqlStr.Append( "'" + name + "',");
sqlStr.Append( "'" + depart + "',");
sqlStr.Append( "'" + role + "',");
sqlStr.Append(1);
sqlStr.Append( ")");

newUserDBAccess.InsertCommand = sqlStr.ToString();
newUserDBAccess.Open();
try
{
if (!newUserDBAccess.ExecuteCommand())
{
errMsg = newUserDBAccess.ErrorMessage;

return false;
}
else
{
return true;
}
}
finally
{
newUserDBAccess.Close();
}

}

Update操作，修改用户信息：

public bool ModifyUser()
{
DBAccess modifyUserDBAccess = new DBAccess();
StringBuilder sqlStr = new StringBuilder();
sqlStr.Append( "update userTable set ");
sqlStr.Append( " usrName = ");
sqlStr.Append( "'" + usrName + "',");
sqlStr.Append( " name =");
sqlStr.Append( "'" + name + "',");
sqlStr.Append( " pwd =");
sqlStr.Append( "'" + pwd + "',");
sqlStr.Append( " depart =");
sqlStr.Append( "'" + depart + "',");
sqlStr.Append( " role =");
sqlStr.Append( "'" + role + "'");
sqlStr.Append( " where usrID = ");
sqlStr.Append(id);

modifyUserDBAccess.UpdateCommand = sqlStr.ToString();
modifyUserDBAccess.Open();
try
{
if (!modifyUserDBAccess.ExecuteCommand())
{
errMsg = modifyUserDBAccess.ErrorMessage;

return false;
}
else
{
return true;
}
}
finally
{
modifyUserDBAccess.Close();
}

}

delUserDBAccess.UpdateCommand = sqlStr.ToString();
delUserDBAccess.Open();
try
{
if (!delUserDBAccess.ExecuteCommand())
{
return false;
}
else
{
return true;
}
}
finally
{
delUserDBAccess.Close();
}

}