SQLiteHelper

本文定义了一个DBHelper类，是SQLite的。需要添加一个System.Data.SQLite的dll，可以到SQLite的官网下载。类的代码如下

using System;
using System.Data;
using System.Data.SQLite;
using System.Configuration;
using System.Collections;

namespace Common
{
    public abstract class SQLiteHelper
    {
        //Data Source=db file fullname
        public static readonly string connectionstring = ConfigurationManager.AppSettings["connectionstring"];

        private static Hashtable parmCache = Hashtable.Synchronized(new Hashtable());

        public static int ExecuteNonQuery(string connectionstring, CommandType commandType, string commandText, params SQLiteParameter[] commandParameters)
        {
            SQLiteCommand cmd = new SQLiteCommand();
            using (SQLiteConnection cn=new SQLiteConnection(connectionstring))
            {
                PrepareCommand(cmd, cn, null, commandType, commandText, commandParameters);
                int result = cmd.ExecuteNonQuery();
                cmd.Parameters.Clear();
                return result;
            }
        }

        public static int ExecuteNonQuery(SQLiteConnection connection, CommandType commandType, string commandText, params SQLiteParameter[] commandParameters)
        {
            SQLiteCommand cmd = new SQLiteCommand();

            PrepareCommand(cmd, connection, null, commandType, commandText, commandParameters);
            int result = cmd.ExecuteNonQuery();
            cmd.Parameters.Clear();
            return result;
        }

        public static int ExecuteNonQuery(SQLiteTransaction trans, CommandType commandType, string commandText, params SQLiteParameter[] commandParameters)
        {
            SQLiteCommand cmd = new SQLiteCommand();

            PrepareCommand(cmd, trans.Connection, trans, commandType, commandText, commandParameters);
            int result = cmd.ExecuteNonQuery();
            cmd.Parameters.Clear();
            return result;
        }

        public static SQLiteDataReader ExecuteReader(string connectionstring,CommandType commandType,string commandText,params SQLiteParameter [] commandParameters)
        {
            SQLiteCommand cmd = new SQLiteCommand();
            SQLiteConnection cn=new SQLiteConnection(connectionstring);
            
            try
            {
                PrepareCommand(cmd, cn, null, commandType, commandText, commandParameters);
                SQLiteDataReader result = null;
                result = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                cmd.Parameters.Clear();
                return result;
            }
            catch 
            {
                cn.Close();
                throw;
            }
            
        }

        public static object ExecuteScalar(string connectionstring, CommandType commandType, string commandText, params SQLiteParameter[] commandParameters)
        {
            SQLiteCommand cmd = new SQLiteCommand();

            using (SQLiteConnection cn=new SQLiteConnection(connectionstring))
            {
                PrepareCommand(cmd, cn, null, commandType, commandText, commandParameters);
                object result = cmd.ExecuteScalar();
                cmd.Parameters.Clear();
                return result;
            }
        }

        public static object ExecuteScalar(SQLiteConnection connection, CommandType commandType, string commandText, params SQLiteParameter[] commandParameters)
        {
            SQLiteCommand cmd = new SQLiteCommand();

            PrepareCommand(cmd, connection, null, commandType, commandText, commandParameters);
            object result = cmd.ExecuteScalar();
            cmd.Parameters.Clear();
            return result;
        }

        public static void CacheParameters(string cacheKey, params SQLiteParameter[] commandParameters)
        {
            parmCache[cacheKey] = commandParameters;
        }

        public static SQLiteParameter[] GetCacheParameters(string cacheKey)
        {
            SQLiteParameter[] cacheParams = (SQLiteParameter[])parmCache[cacheKey];

            if (cacheParams == null) return null;

            int cacheLength=cacheParams.Length;
            SQLiteParameter[] cloneParams=new SQLiteParameter[cacheLength];

            for (int i = 0; i < cacheLength; i++)
                cloneParams[i] = (SQLiteParameter)((ICloneable)cacheParams[i]).Clone();

            return cloneParams;
        }

        private static void PrepareCommand(SQLiteCommand command, SQLiteConnection connection, SQLiteTransaction trans, CommandType commandType, string commandText, SQLiteParameter[] commandParameters)
        {
            command.Connection = connection;
            command.CommandType = commandType;
            command.CommandText = commandText;

            if (commandParameters != null) 
                command.Parameters.AddRange(commandParameters);

            if (trans != null)
                command.Transaction = trans;

            if (connection.State != ConnectionState.Open)
                connection.Open();
        }
    }
}