蛙蛙推荐：神马ORM都是浮云，看看史上最简单最好用的OleDbHelper

摘要：大多数据库都支持OleDb，OleDb的参数化查询不支持命名参数，参数用?表示就行，赋值是按顺序赋值的。今天把Sqlserver迁移到Access，顺手写了个简单的OleDbHelper，由于OleDb的通用性，应该也可以访问其它的数据库，而且参数化查询也不怕sql注入，性能应该也会太差。

以下为完整代码，不到50行

class OledbHelper
{
    private string _strconn;
    public OledbHelper(string strconn)
    {
        _strconn = strconn;
    }
    public T ExecuteScalar<T>(string sql, params object[] args)
    {
        using (OleDbConnection conn = new OleDbConnection(_strconn))
        {
            return (T)MakeCommand(conn, sql, args).ExecuteScalar();                
        }
    }
    public void ExecuteNonQuery(string sql, params object[] args)
    {
        using (OleDbConnection conn = new OleDbConnection(_strconn))
        {
            MakeCommand(conn, sql, args).ExecuteNonQuery();
        }          
    }
    public IDataReader ExecuteReader(string sql, params object[] args)
    {
        OleDbConnection conn = new OleDbConnection(_strconn);
        try
        {
            OleDbCommand cmd = MakeCommand(conn, sql, args);
            return cmd.ExecuteReader(CommandBehavior.CloseConnection);
        }
        catch
        {
            conn.Close();
            throw;
        }
    }
    public OleDbCommand MakeCommand(OleDbConnection conn, string sql, params object[] args)
    {
        OleDbCommand cmd = new OleDbCommand(sql, conn);
        if (conn.State != ConnectionState.Open)
            conn.Open();
        for (int i = 0; i < args.Length; i++)
        {
            cmd.Parameters.AddWithValue(i.ToString(), args[i]);
        }
        return cmd;
    }
}

　　使用示例

//获取单个值
public static string GetTagName(byte tagid)
{
    return _db.ExecuteScalar<string>("select TagName from Liwu_Tags where TagId=?", tagid);
}
//普通查询，参数的赋值很自然简单，代码最终也很简短
//需要注意的是access的"日期/时间"列不能用DateTime类型赋值，要ToString一下，如下
public static void AddTags(long itemid, IEnumerable<byte> tagids)
{

    foreach (var tagid in tagids)
    {
        if (!_db.ExecuteReader("select * from Liwu_TagLines where ItemId=? and TagId=?", itemid, tagid).Read())
        {
            _db.ExecuteNonQuery("insert into Liwu_TagLines values (?,?,?)",
                tagid, itemid, DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss"));
        }
    }

}
//带条件的分页查询，性能还行，查询出来的DataReader可以直接去绑定数据控件去
//分页sql有些长，所以代码有些乱，好在修改的地方不太多
public static IDataReader GetItems(int page = 1, int tagid = -1)
{
    const int pagesize = 12;
    string sql1 = string.Empty;
    if (tagid == -1)
        sql1 = string.Format("select top {0} * from Liwu_Items order by CreateTime desc", page * pagesize);
    else
        sql1 = string.Format("select top {0} item.* from Liwu_Items as item inner join Liwu_TagLines as line"
            + " on line.ItemId = item.ItemId  where tagid= ? order by item.CreateTime desc", pagesize * page);
    string sql2 = string.Format("select top {0} * from ({1}) order by CreateTime", pagesize, sql1);
    string sql = string.Format("select * from ({0}) order by CreateTime desc", sql2);

    return tagid == -1 ? _db.ExecuteReader(sql) : _db.ExecuteReader(sql, tagid);
}