C#如何使用数据库

     数据库，在我们开发项目中那是最常见的了，无论复杂的项目、还是简单的项目，只要涉及数据的操作（增删改查），都会用到数据库。当然使用的数据库的种类根据项目的需求不同，也是不同的。在我所做的项目中就是用过ACCESS 2000、SQL Server 2000、Oracle 10g，因此简单总结下c#如何使用数据库的。程序执行sql语句（包括单条sql，多条sql，存储过程，函数等等）大体有三个步骤：连接数据库，执行sql语句，返回结果。那么我们来看看c#是如何完成这三个步骤的。无论哪种数据库都是这三个步骤，那么就不按数据库分了，按照返回结果的类型来分类吧。

数据库连接用的字符串：

即下面代码的connstr

"Provider=Microsoft.Jet.OLEDB.4.0;Data Source="数据库路径";Persist Security Info=True;Jet OLEDB:Database Password="密码"

1、  执行sql语句返回受影响的行数

(1)、一条sql语句

        public static int ExecuteNonQuery(string connStr, string sql)        {            OleDbConnection conn = null;            try            {                conn = new OleDbConnection(connStr);                conn.Open();                OleDbCommand command = new OleDbCommand(sql, conn);                return command.ExecuteNonQuery();            }            catch            {                return 0;            }            finally            {                if (conn != null)                    conn.Close();            }        }

(2)、多条sql语句,返回受影响行数。由于多条sql为了保证数据库的正确性，最好使用事务方式运行。

        public static int ExecuteNonQuery(string connStr, List<string> sqlList)        {            int executeCount = 0;            OleDbTransaction transaction = null;            OleDbConnection conn = null;            try            {                conn = new OleDbConnection(connStr);                conn.Open();                transaction = conn.BeginTransaction();                OleDbCommand command = new OleDbCommand();                command.Connection = conn;                command.Transaction = transaction;                for (int i = 0; i < sqlList.Count; i++)                {                    command.CommandText = sqlList[i];                    executeCount += command.ExecuteNonQuery();                }                transaction.Commit();            }            catch            {                if (transaction != null)                    transaction.Rollback();                return 0;            }            finally            {                if (conn != null)                    conn.Close();            }            return executeCount;        }

2、返回DataSet

        public static DataSet ExecuteQueryReturnDataSet(string connStr, string sql)        {            OleDbConnection conn = null;            DataSet ds = null;            try            {                conn = new OleDbConnection(connStr);                ds = new DataSet();                conn.Open();                OleDbDataAdapter command = new OleDbDataAdapter(sql, conn);                command.Fill(ds, "datasetName");            }            catch            {            }            finally            {                if (conn != null)                    conn.Close();            }            return ds;        }

3、返回OleDbDataReader

        public static OleDbDataReader ExecuteQueryReturnReader(string sql, string connStr)        {            OleDbConnection conn = new OleDbConnection();            OleDbDataReader reader = null;            try            {                conn = new OleDbConnection(connStr);                conn.Open();                OleDbCommand command = conn.CreateCommand();                command.CommandText = sql;                reader = command.ExecuteReader();            }            catch            {            }            finally            {                if (conn != null)                    conn.Close();            }            return reader;        }    

4、执行存储过程并返回受影响行数(以Oracle为例)

        public static int RunProcedure(string storedProcName, IDataParameter[] parameters)        {            int result = 0;             try            {                using (OracleConnection connection = new OracleConnection(GetConnectionString()))                {                    connection.Open();                     OracleCommand command = BuildQueryCommand(connection, storedProcName, parameters);                     result = command.ExecuteNonQuery();                }            }            catch (Exception e)            {            }             return result;        }        private static OracleCommand BuildQueryCommand(OracleConnection connection, string storedProcName,             IDataParameter[] parameters)        {            OracleCommand command = new OracleCommand(storedProcName, connection);             command.CommandType = CommandType.StoredProcedure;             foreach (OracleParameter parameter in parameters)            {                command.Parameters.Add(parameter);            }            return command;        }  

5、带参数的sql语句

        public static int ExecuteNonQuery(string sql,string connStr, OleDbParameter[] commandParameters)        {            int count = 0;            OleDbCommand cmd = new OleDbCommand();             OleDbConnection conn = null;            try            {                conn = new OleDbConnection(connStr);                PrepareCommand(cmd, conn,sql, commandParameters);                count = cmd.ExecuteNonQuery();                cmd.Parameters.Clear();            }            catch            {            }            finally            {                if (conn != null)                {                    conn.Close();                }            }            return count;        }        private static void PrepareCommand(OleDbCommand cmd, OleDbConnection conn, string sql, OleDbParameter[] cmdParms)        {            if (conn.State != ConnectionState.Open)                conn.Open();             cmd.Connection = conn;            cmd.CommandText = sql;            cmd.CommandType = CommandType.Text;             if (cmdParms != null)            {                foreach (OleDbParameter parm in cmdParms)                    cmd.Parameters.Add(parm);            }        }   

一般常用的就这么几种，数据库的几个重要对象分别是：OleDbCommand、OleDbConnection、OleDbDataReader、OleDbDataAdapter、DataSet。对于不同数据库，有几个对象需要对应相应数据库的对象。OleDbCommand、OleDbConnection、OleDbDataReader、OleDbDataAdapter,Oracle下OleDb换成Oracle，Sql Server下 则换成SQL。

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