连接数据库、对数据库的增、删、改、查

[c#]代码库

 public class SqlHelper
    {
        //数据库连接词
        private static string constr = System.Configuration.ConfigurationManager.ConnectionStrings["constr"].ToString();

        /// <summary>
        /// SQL语句 无参查询
        /// </summary>
        /// <param name="sql">select 语句</param>
        /// <returns>返回SqlDataReader</returns>
        public static SqlDataReader Query(string sql)
        {
            SqlConnection conn = new SqlConnection(constr);
            try
            {
                if (conn.State != ConnectionState.Open)
                    conn.Open();
                SqlCommand cmd = new SqlCommand(sql, conn);
                return cmd.ExecuteReader(CommandBehavior.CloseConnection);
            }
            catch
            {
                if(conn.State==ConnectionState.Open)
                {
                    conn.Close();
                }
                throw;
            }
        }

        /// <summary>
        /// SQL语句 有参查询
        /// </summary>
        /// <param name="sql">select 语句</param>
        /// <param name="para">SQL参数</param>
        /// <returns>返回SqlDataReader</returns>
        public static SqlDataReader Query(string sql, SqlParameter[] para)
        {
            SqlConnection conn = new SqlConnection(constr);
            try
            {
                if (conn.State != ConnectionState.Open)
                    conn.Open();
                SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.Parameters.AddRange(para);
                return cmd.ExecuteReader(CommandBehavior.CloseConnection);
            }
            catch
            {
                if(conn.State==ConnectionState.Open)
                {
                    conn.Close();
                }
                throw;
            }
        }

        /// <summary>
        /// SQL语句 单一结果的无参查询
        /// </summary>
        /// <param name="sql">select 语句</param>
        /// <returns>返回 object</returns>
        public static object QueryScalar(string sql)
        {
            using (SqlConnection conn = new SqlConnection(constr))
            {
                if (conn.State != ConnectionState.Open)
                    conn.Open();
                SqlCommand cmd = new SqlCommand(sql, conn);
                return cmd.ExecuteScalar();
            }
        }

        /// <summary>
        /// SQL语句 单一结果的有参查询
        /// </summary>
        /// <param name="sql">select 语句</param>
        /// <param name="para">SQL参数</param>
        /// <returns>返回 object</returns>
        public static object QueryScalar(string sql,SqlParameter[] para)
        {
            using (SqlConnection conn = new SqlConnection(constr))
            {
                if (conn.State != ConnectionState.Open)
                    conn.Open();
                SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.Parameters.AddRange(para);
                return cmd.ExecuteScalar();
            }
        }

        /// <summary>
        /// SQL语句 无参增，删，改
        /// </summary>
        /// <param name="sql">insert,update,delete语句</param>
        /// <returns>返回影响的行数</returns>
        public static int NonQuery(string sql)
        {
            SqlConnection conn = new SqlConnection(constr);
            SqlTransaction tran = null;
            try
            {
                conn.Open();
                tran = conn.BeginTransaction();
                SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.Transaction = tran;
                int i = cmd.ExecuteNonQuery();
                tran.Commit();
                return i;
            }
            catch
            {
                if (tran != null)
                    tran.Rollback();
                throw;
            }
            finally
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
            }
        }

        /// <summary>
        /// SQL语句 有参增，删，改
        /// </summary>
        /// <param name="sql">insert,update,delete语句</param>
        /// <param name="para">SQL参数</param>
        /// <returns>返回影响的行数</returns>
        public static int NonQuery(string sql,SqlParameter[] para)
        {
            SqlConnection conn = new SqlConnection(constr);
            SqlTransaction tran = null;
            try
            {
                conn.Open();
                tran = conn.BeginTransaction();
                SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.Parameters.AddRange(para);
                cmd.Transaction = tran;
                int i = cmd.ExecuteNonQuery();
                tran.Commit();
                return i;
            }
            catch (Exception e)
            {
                if (tran != null)
                    tran.Rollback();
                throw;
            }
            finally
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
            }
        }
    }