C#操作SQLite数据库
SQLite介绍
SQLite is a software library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine.
SQLite是一个开源、免费的小型RDBMS(关系型数据库)，能独立运行、无服务器、零配置、支持事物，用C实现，内存占用较小，支持绝大数的SQL92标准。
SQLite数据库官方主页：http://www.sqlite.org/index.html
C#操作SQLite Database
C#下SQLite操作驱动dll下载：System.Data.SQLite
C#使用SQLite步骤：
（1）新建一个project
（2）添加SQLite操作驱动dll引用
（3）使用API操作SQLite DataBase
using System;
using System.Data.SQLite;
namespace SQLiteSamples
{
class Program
{
//数据库连接
SQLiteConnection m_dbConnection;
static void Main(string[] args)
{
Program p = new Program();
}
public Program()
{
createNewDatabase();
connectToDatabase();
createTable();
fillTable();
printHighscores();
}
//创建一个空的数据库
void createNewDatabase()
{
SQLiteConnection.CreateFile("MyDatabase.sqlite");
}
//创建一个连接到指定数据库
void connectToDatabase()
{
m_dbConnection = new SQLiteConnection("Data Source=MyDatabase.sqlite;Version=3;");
m_dbConnection.Open();
}
//在指定数据库中创建一个table
void createTable()
{
string sql = "create table highscores (name varchar(20), score int)";
SQLiteCommand command = new SQLiteCommand(sql, m_dbConnection);
command.ExecuteNonQuery();
}
//插入一些数据
void fillTable()
{
string sql = "insert into highscores (name, score) values ('Me', 3000)";
SQLiteCommand command = new SQLiteCommand(sql, m_dbConnection);
command.ExecuteNonQuery();
sql = "insert into highscores (name, score) values ('Myself', 6000)";
command = new SQLiteCommand(sql, m_dbConnection);
command.ExecuteNonQuery();
sql = "insert into highscores (name, score) values ('And I', 9001)";
command = new SQLiteCommand(sql, m_dbConnection);
command.ExecuteNonQuery();
}
//使用sql查询语句，并显示结果
void printHighscores()
{
string sql = "select * from highscores order by score desc";
SQLiteCommand command = new SQLiteCommand(sql, m_dbConnection);
SQLiteDataReader reader = command.ExecuteReader();
while (reader.Read())
Console.WriteLine("Name: " + reader["name"] + "\tScore: " + reader["score"]);
Console.ReadLine();
}
}
}
关于SQLite的connection string说明：http://www.connectionstrings.com/sqlite/
SQLite GUI客户端列表：http://www.sqlite.org/cvstrac/wiki?p=ManagementTools
SQLite Administrator下载地址：http://download.orbmu2k.de/files/sqliteadmin.zip
操作SQLite Database的C#帮助类SQLite Helper
将一些常用的功能封装一下，封装成SQLite Helper类
using System;
using System.Data;
using System.Text.RegularExpressions;
using System.Xml;
using System.IO;
using System.Collections;
using System.Data.SQLite;
namespace DBUtility.SQLite
{
/// <summary>
/// SQLiteHelper is a utility class similar to "SQLHelper" in MS
/// Data Access Application Block and follows similar pattern.
/// </summary>
public class SQLiteHelper
{
/// <summary>
/// Creates a new <see cref="SQLiteHelper"/> instance. The ctor is marked private since all members are static.
/// </summary>
private SQLiteHelper()
{
}
/// <summary>
/// Creates the command.
/// </summary>
/// <param name="connection">Connection.</param>
/// <param name="commandText">Command text.</param>
/// <param name="commandParameters">Command parameters.</param>
/// <returns>SQLite Command</returns>
public static SQLiteCommand CreateCommand(SQLiteConnection connection, string commandText, params SQLiteParameter[] commandParameters)
{
SQLiteCommand cmd = new SQLiteCommand(commandText, connection);
if (commandParameters.Length > 0)
{
foreach (SQLiteParameter parm in commandParameters)
cmd.Parameters.Add(parm);
}
return cmd;
}
/// <summary>
/// Creates the command.
/// </summary>
/// <param name="connectionString">Connection string.</param>
/// <param name="commandText">Command text.</param>
/// <param name="commandParameters">Command parameters.</param>
/// <returns>SQLite Command</returns>
public static SQLiteCommand CreateCommand(string connectionString, string commandText, params SQLiteParameter[] commandParameters)
{
SQLiteConnection cn = new SQLiteConnection(connectionString);
SQLiteCommand cmd = new SQLiteCommand(commandText, cn);
if (commandParameters.Length > 0)
{
foreach (SQLiteParameter parm in commandParameters)
cmd.Parameters.Add(parm);
}
return cmd;
}
/// <summary>
/// Creates the parameter.
/// </summary>
/// <param name="parameterName">Name of the parameter.</param>
/// <param name="parameterType">Parameter type.</param>
/// <param name="parameterValue">Parameter value.</param>
/// <returns>SQLiteParameter</returns>
public static SQLiteParameter CreateParameter(string parameterName, System.Data.DbType parameterType, object parameterValue)
{
SQLiteParameter parameter = new SQLiteParameter();
parameter.DbType = parameterType;
parameter.ParameterName = parameterName;
parameter.Value = parameterValue;
return parameter;
}
/// <summary>
/// Shortcut method to execute dataset from SQL Statement and object[] arrray of parameter values
/// </summary>
/// <param name="connectionString">SQLite Connection string</param>
/// <param name="commandText">SQL Statement with embedded "@param" style parameter names</param>
/// <param name="paramList">object[] array of parameter values</param>
/// <returns></returns>
public static DataSet ExecuteDataSet(string connectionString, string commandText, object[] paramList)
{
SQLiteConnection cn = new SQLiteConnection(connectionString);
SQLiteCommand cmd = cn.CreateCommand();
cmd.CommandText = commandText;
if (paramList != null)
{
AttachParameters(cmd,commandText, paramList);
}
DataSet ds = new DataSet();
if (cn.State == ConnectionState.Closed)
cn.Open();
SQLiteDataAdapter da = new SQLiteDataAdapter(cmd);
da.Fill(ds);
da.Dispose();
cmd.Dispose();
cn.Close();
return ds;
}
/// <summary>
/// Shortcut method to execute dataset from SQL Statement and object[] arrray of parameter values
/// </summary>
/// <param name="cn">Connection.</param>
/// <param name="commandText">Command text.</param>
/// <param name="paramList">Param list.</param>
/// <returns></returns>
public static DataSet ExecuteDataSet(SQLiteConnection cn, string commandText, object[] paramList)
{
SQLiteCommand cmd = cn.CreateCommand();
cmd.CommandText = commandText;
if (paramList != null)
{
AttachParameters(cmd,commandText, paramList);
}
DataSet ds = new DataSet();
if (cn.State == ConnectionState.Closed)
cn.Open();
SQLiteDataAdapter da = new SQLiteDataAdapter(cmd);
da.Fill(ds);
da.Dispose();
cmd.Dispose();
cn.Close();
return ds;
}
/// <summary>
/// Executes the dataset from a populated Command object.
/// </summary>
/// <param name="cmd">Fully populated SQLiteCommand</param>
/// <returns>DataSet</returns>
public static DataSet ExecuteDataset(SQLiteCommand cmd)
{
if (cmd.Connection.State == ConnectionState.Closed)
cmd.Connection.Open();
DataSet ds = new DataSet();
SQLiteDataAdapter da = new SQLiteDataAdapter(cmd);
da.Fill(ds);
da.Dispose();
cmd.Connection.Close();
cmd.Dispose();
return ds;
}
/// <summary>
/// Executes the dataset in a SQLite Transaction
/// </summary>
/// <param name="transaction">SQLiteTransaction. Transaction consists of Connection, Transaction, /// and Command, all of which must be created prior to making this method call. </param>
/// <param name="commandText">Command text.</param>
/// <param name="commandParameters">Sqlite Command parameters.</param>
/// <returns>DataSet</returns>
/// <remarks>user must examine Transaction Object and handle transaction.connection .Close, etc.</remarks>
public static DataSet ExecuteDataset(SQLiteTransaction transaction, string commandText, params SQLiteParameter[] commandParameters)
{
if (transaction == null) throw new ArgumentNullException("transaction");
if (transaction != null && transaction.Connection == null) throw new ArgumentException("The transaction was rolled back or committed, please provide an open transaction.", "transaction");
IDbCommand cmd = transaction.Connection.CreateCommand();
cmd.CommandText = commandText;
foreach (SQLiteParameter parm in commandParameters)
{
cmd.Parameters.Add(parm);
}
if (transaction.Connection.State == ConnectionState.Closed)
transaction.Connection.Open();
DataSet ds = ExecuteDataset((SQLiteCommand)cmd);
return ds;
}
/// <summary>
/// Executes the dataset with Transaction and object array of parameter values.
/// </summary>
/// <param name="transaction">SQLiteTransaction. Transaction consists of Connection, Transaction, /// and Command, all of which must be created prior to making this method call. </param>
/// <param name="commandText">Command text.</param>
/// <param name="commandParameters">object[] array of parameter values.</param>
/// <returns>DataSet</returns>
/// <remarks>user must examine Transaction Object and handle transaction.connection .Close, etc.</remarks>
public static DataSet ExecuteDataset(SQLiteTransaction transaction, string commandText, object[] commandParameters)
{
if (transaction == null) throw new ArgumentNullException("transaction");
if (transaction != null && transaction.Connection == null) throw new ArgumentException("The transaction was rolled back or committed, please provide an open transaction.", "transaction");
IDbCommand cmd = transaction.Connection.CreateCommand();
cmd.CommandText = commandText;
AttachParameters((SQLiteCommand)cmd,cmd.CommandText, commandParameters);
if (transaction.Connection.State == ConnectionState.Closed)
transaction.Connection.Open();
DataSet ds = ExecuteDataset((SQLiteCommand)cmd);
return ds;
}
#region UpdateDataset
/// <summary>
/// Executes the respective command for each inserted, updated, or deleted row in the DataSet.
/// </summary>
/// <remarks>
/// e.g.:
/// UpdateDataset(conn, insertCommand, deleteCommand, updateCommand, dataSet, "Order");
/// </remarks>
/// <param name="insertCommand">A valid SQL statement to insert new records into the data source</param>
/// <param name="deleteCommand">A valid SQL statement to delete records from the data source</param>
/// <param name="updateCommand">A valid SQL statement used to update records in the data source</param>
/// <param name="dataSet">The DataSet used to update the data source</param>
/// <param name="tableName">The DataTable used to update the data source.</param>
public static void UpdateDataset(SQLiteCommand insertCommand, SQLiteCommand deleteCommand, SQLiteCommand updateCommand, DataSet dataSet, string tableName)
{
if (insertCommand == null) throw new ArgumentNullException("insertCommand");
if (deleteCommand == null) throw new ArgumentNullException("deleteCommand");
if (updateCommand == null) throw new ArgumentNullException("updateCommand");
if (tableName == null || tableName.Length == 0) throw new ArgumentNullException("tableName");
// Create a SQLiteDataAdapter, and dispose of it after we are done
using (SQLiteDataAdapter dataAdapter = new SQLiteDataAdapter())
{
// Set the data adapter commands
dataAdapter.UpdateCommand = updateCommand;
dataAdapter.InsertCommand = insertCommand;
dataAdapter.DeleteCommand = deleteCommand;
// Update the dataset changes in the data source
dataAdapter.Update(dataSet, tableName);
// Commit all the changes made to the DataSet
dataSet.AcceptChanges();
}
}
#endregion
/// <summary>
/// ShortCut method to return IDataReader
/// NOTE: You should explicitly close the Command.connection you passed in as
/// well as call Dispose on the Command after reader is closed.
/// We do this because IDataReader has no underlying Connection Property.
/// </summary>
/// <param name="cmd">SQLiteCommand Object</param>
/// <param name="commandText">SQL Statement with optional embedded "@param" style parameters</param>
/// <param name="paramList">object[] array of parameter values</param>
/// <returns>IDataReader</returns>
public static IDataReader ExecuteReader(SQLiteCommand cmd, string commandText, object[] paramList)
{
if (cmd.Connection == null)
throw new ArgumentException("Command must have live connection attached.", "cmd");
cmd.CommandText = commandText;
AttachParameters(cmd,commandText, paramList);
if (cmd.Connection.State == ConnectionState.Closed)
cmd.Connection.Open();
IDataReader rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
return rdr;
}
/// <summary>
/// Shortcut to ExecuteNonQuery with SqlStatement and object[] param values
/// </summary>
/// <param name="connectionString">SQLite Connection String</param>
/// <param name="commandText">Sql Statement with embedded "@param" style parameters</param>
/// <param name="paramList">object[] array of parameter values</param>
/// <returns></returns>
public static int ExecuteNonQuery(string connectionString, string commandText, params object[] paramList)
{
SQLiteConnection cn = new SQLiteConnection(connectionString);
SQLiteCommand cmd = cn.CreateCommand();
cmd.CommandText = commandText;
AttachParameters(cmd,commandText, paramList);
if (cn.State == ConnectionState.Closed)
cn.Open();
int result = cmd.ExecuteNonQuery();
cmd.Dispose();
cn.Close();
return result;
}
public static int ExecuteNonQuery(SQLiteConnection cn, string commandText, params object[] paramList)
{
SQLiteCommand cmd = cn.CreateCommand();
cmd.CommandText = commandText;
AttachParameters(cmd,commandText, paramList);
if (cn.State == ConnectionState.Closed)
cn.Open();
int result = cmd.ExecuteNonQuery();
cmd.Dispose();
cn.Close();
return result;
}
/// <summary>
/// Executes non-query sql Statment with Transaction
/// </summary>
/// <param name="transaction">SQLiteTransaction. Transaction consists of Connection, Transaction, /// and Command, all of which must be created prior to making this method call. </param>
/// <param name="commandText">Command text.</param>
/// <param name="paramList">Param list.</param>
/// <returns>Integer</returns>
/// <remarks>user must examine Transaction Object and handle transaction.connection .Close, etc.</remarks>
public static int ExecuteNonQuery(SQLiteTransaction transaction, string commandText, params object[] paramList)
{
if (transaction == null) throw new ArgumentNullException("transaction");
if (transaction != null && transaction.Connection == null) throw new ArgumentException("The transaction was rolled back or committed, please provide an open transaction.", "transaction");
IDbCommand cmd = transaction.Connection.CreateCommand();
cmd.CommandText = commandText;
AttachParameters((SQLiteCommand)cmd,cmd.CommandText, paramList);
if (transaction.Connection.State == ConnectionState.Closed)
transaction.Connection.Open();
int result = cmd.ExecuteNonQuery();
cmd.Dispose();
return result;
}
/// <summary>
/// Executes the non query.
/// </summary>
/// <param name="cmd">CMD.</param>
/// <returns></returns>
public static int ExecuteNonQuery(IDbCommand cmd)
{
if (cmd.Connection.State == ConnectionState.Closed)
cmd.Connection.Open();
int result = cmd.ExecuteNonQuery();
cmd.Connection.Close();
cmd.Dispose();
return result;
}
/// <summary>
/// Shortcut to ExecuteScalar with Sql Statement embedded params and object[] param values
/// </summary>
/// <param name="connectionString">SQLite Connection String</param>
/// <param name="commandText">SQL statment with embedded "@param" style parameters</param>
/// <param name="paramList">object[] array of param values</param>
/// <returns></returns>
public static object ExecuteScalar(string connectionString, string commandText, params object[] paramList)
{
SQLiteConnection cn = new SQLiteConnection(connectionString);
SQLiteCommand cmd = cn.CreateCommand();
cmd.CommandText = commandText;
AttachParameters(cmd,commandText, paramList);
if (cn.State == ConnectionState.Closed)
cn.Open();
object result = cmd.ExecuteScalar();
cmd.Dispose();
cn.Close();
return result;
}
/// <summary>
/// Execute XmlReader with complete Command
/// </summary>
/// <param name="command">SQLite Command</param>
/// <returns>XmlReader</returns>
public static XmlReader ExecuteXmlReader(IDbCommand command)
{ // open the connection if necessary, but make sure we
// know to close it when we�re done.
if (command.Connection.State != ConnectionState.Open)
{
command.Connection.Open();
}
// get a data adapter
SQLiteDataAdapter da = new SQLiteDataAdapter((SQLiteCommand)command);
DataSet ds = new DataSet();
// fill the data set, and return the schema information
da.MissingSchemaAction = MissingSchemaAction.AddWithKey;
da.Fill(ds);
// convert our dataset to XML
StringReader stream = new StringReader(ds.GetXml());
command.Connection.Close();
// convert our stream of text to an XmlReader
return new XmlTextReader(stream);
}
/// <summary>
/// Parses parameter names from SQL Statement, assigns values from object array , /// and returns fully populated ParameterCollection.
/// </summary>
/// <param name="commandText">Sql Statement with "@param" style embedded parameters</param>
/// <param name="paramList">object[] array of parameter values</param>
/// <returns>SQLiteParameterCollection</returns>
/// <remarks>Status experimental. Regex appears to be handling most issues. Note that parameter object array must be in same ///order as parameter names appear in SQL statement.</remarks>
private static SQLiteParameterCollection AttachParameters(SQLiteCommand cmd, string commandText, params object[] paramList)
{
if (paramList == null || paramList.Length == 0) return null;
SQLiteParameterCollection coll = cmd.Parameters;
string parmString = commandText.Substring(commandText.IndexOf("@"));
// pre-process the string so always at least 1 space after a comma.
parmString = parmString.Replace(",", " ,");
// get the named parameters into a match collection
string pattern = @"(@)\S*(.*?)\b";
Regex ex = new Regex(pattern, RegexOptions.IgnoreCase);
MatchCollection mc = ex.Matches(parmString);
string[] paramNames = new string[mc.Count];
int i = 0;
foreach (Match m in mc)
{
paramNames[i] = m.Value;
i++;
}
// now let's type the parameters
int j = 0;
Type t = null;
foreach (object o in paramList)
{
t = o.GetType();
SQLiteParameter parm = new SQLiteParameter();
switch (t.ToString())
{
case ("DBNull"):
case ("Char"):
case ("SByte"):
case ("UInt16"):
case ("UInt32"):
case ("UInt64"):
throw new SystemException("Invalid data type");
case ("System.String"):
parm.DbType = DbType.String;
parm.ParameterName = paramNames[j];
parm.Value = (string)paramList[j];
coll.Add(parm);
break;
case ("System.Byte[]"):
parm.DbType = DbType.Binary;
parm.ParameterName = paramNames[j];
parm.Value = (byte[])paramList[j];
coll.Add(parm);
break;
case ("System.Int32"):
parm.DbType = DbType.Int32;
parm.ParameterName = paramNames[j];
parm.Value = (int)paramList[j];
coll.Add(parm);
break;
case ("System.Boolean"):
parm.DbType = DbType.Boolean;
parm.ParameterName = paramNames[j];
parm.Value = (bool)paramList[j];
coll.Add(parm);
break;
case ("System.DateTime"):
parm.DbType = DbType.DateTime;
parm.ParameterName = paramNames[j];
parm.Value = Convert.ToDateTime(paramList[j]);
coll.Add(parm);
break;
case ("System.Double"):
parm.DbType = DbType.Double;
parm.ParameterName = paramNames[j];
parm.Value = Convert.ToDouble(paramList[j]);
coll.Add(parm);
break;
case ("System.Decimal"):
parm.DbType = DbType.Decimal;
parm.ParameterName = paramNames[j];
parm.Value = Convert.ToDecimal(paramList[j]);
break;
case ("System.Guid"):
parm.DbType = DbType.Guid;
parm.ParameterName = paramNames[j];
parm.Value = (System.Guid)(paramList[j]);
break;
case ("System.Object"):
parm.DbType = DbType.Object;
parm.ParameterName = paramNames[j];
parm.Value = paramList[j];
coll.Add(parm);
break;
default:
throw new SystemException("Value is of unknown data type");
} // end switch
j++;
}
return coll;
}
/// <summary>
/// Executes non query typed params from a DataRow
/// </summary>
/// <param name="command">Command.</param>
/// <param name="dataRow">Data row.</param>
/// <returns>Integer result code</returns>
public static int ExecuteNonQueryTypedParams(IDbCommand command, DataRow dataRow)
{
int retVal = 0;
// If the row has values, the store procedure parameters must be initialized
if (dataRow != null && dataRow.ItemArray.Length > 0)
{
// Set the parameters values
AssignParameterValues(command.Parameters, dataRow);
retVal = ExecuteNonQuery(command);
}
else
{
retVal = ExecuteNonQuery(command);
}
return retVal;
}
/// <summary>
/// This method assigns dataRow column values to an IDataParameterCollection
/// </summary>
/// <param name="commandParameters">The IDataParameterCollection to be assigned values</param>
/// <param name="dataRow">The dataRow used to hold the command's parameter values</param>
/// <exception cref="System.InvalidOperationException">Thrown if any of the parameter names are invalid.</exception>
protected internal static void AssignParameterValues(IDataParameterCollection commandParameters, DataRow dataRow)
{
if (commandParameters == null || dataRow == null)
{
// Do nothing if we get no data
return;
}
DataColumnCollection columns = dataRow.Table.Columns;
int i = 0;
// Set the parameters values
foreach (IDataParameter commandParameter in commandParameters)
{
// Check the parameter name
if (commandParameter.ParameterName == null ||
commandParameter.ParameterName.Length <= 1)
throw new InvalidOperationException(string.Format(
"Please provide a valid parameter name on the parameter #{0}, the ParameterName property has the following value: '{1}'.",
i, commandParameter.ParameterName));
if (columns.Contains(commandParameter.ParameterName))
commandParameter.Value = dataRow[commandParameter.ParameterName];
else if (columns.Contains(commandParameter.ParameterName.Substring(1)))
commandParameter.Value = dataRow[commandParameter.ParameterName.Substring(1)];
i++;
}
}
/// <summary>
/// This method assigns dataRow column values to an array of IDataParameters
/// </summary>
/// <param name="commandParameters">Array of IDataParameters to be assigned values</param>
/// <param name="dataRow">The dataRow used to hold the stored procedure's parameter values</param>
/// <exception cref="System.InvalidOperationException">Thrown if any of the parameter names are invalid.</exception>
protected void AssignParameterValues(IDataParameter[] commandParameters, DataRow dataRow)
{
if ((commandParameters == null) || (dataRow == null))
{
// Do nothing if we get no data
return;
}
DataColumnCollection columns = dataRow.Table.Columns;
int i = 0;
// Set the parameters values
foreach (IDataParameter commandParameter in commandParameters)
{
// Check the parameter name
if (commandParameter.ParameterName == null ||
commandParameter.ParameterName.Length <= 1)
throw new InvalidOperationException(string.Format(
"Please provide a valid parameter name on the parameter #{0}, the ParameterName property has the following value: '{1}'.",
i, commandParameter.ParameterName));
if (columns.Contains(commandParameter.ParameterName))
commandParameter.Value = dataRow[commandParameter.ParameterName];
else if (columns.Contains(commandParameter.ParameterName.Substring(1)))
commandParameter.Value = dataRow[commandParameter.ParameterName.Substring(1)];
i++;
}
}
/// <summary>
/// This method assigns an array of values to an array of IDataParameters
/// </summary>
/// <param name="commandParameters">Array of IDataParameters to be assigned values</param>
/// <param name="parameterValues">Array of objects holding the values to be assigned</param>
/// <exception cref="System.ArgumentException">Thrown if an incorrect number of parameters are passed.</exception>
protected void AssignParameterValues(IDataParameter[] commandParameters, params object[] parameterValues)
{
if ((commandParameters == null) || (parameterValues == null))
{
// Do nothing if we get no data
return;
}
// We must have the same number of values as we pave parameters to put them in
if (commandParameters.Length != parameterValues.Length)
{
throw new ArgumentException("Parameter count does not match Parameter Value count.");
}
// Iterate through the IDataParameters, assigning the values from the corresponding position in the
// value array
for (int i = 0, j = commandParameters.Length, k = 0; i < j; i++)
{
if (commandParameters[i].Direction != ParameterDirection.ReturnValue)
{
// If the current array value derives from IDataParameter, then assign its Value property
if (parameterValues[k] is IDataParameter)
{
IDataParameter paramInstance;
paramInstance = (IDataParameter)parameterValues[k];
if (paramInstance.Direction == ParameterDirection.ReturnValue)
{
paramInstance = (IDataParameter)parameterValues[++k];
}
if (paramInstance.Value == null)
{
commandParameters[i].Value = DBNull.Value;
}
else
{
commandParameters[i].Value = paramInstance.Value;
}
}
else if (parameterValues[k] == null)
{
commandParameters[i].Value = DBNull.Value;
}
else
{
commandParameters[i].Value = parameterValues[k];
}
k++;
}
}
}
}
}
Codeproject上的一个封装：http://www.codeproject.com/Articles/746191/SQLite-Helper-Csharp