防止查询数据返回数据行为零引起的逻辑判断重复或抛出异常

以下代码以操作ORACLE数据库为例

1.返回DataSet数据，若查询返回行数为零，返回null

 1         /// <summary>
 2         /// 执行查询语句，返回DataSet
 3         /// </summary>
 4         /// <param name="SQLString">查询语句</param>
 5         /// <returns>DataSet</returns>
 6         public static DataSet Query(string SQLString, params OracleParameter[] cmdParms)
 7         {
 8             using (OracleConnection connection = new OracleConnection(connectionString))
 9             {
10                 OracleCommand cmd = new OracleCommand();
11                 PrepareCommand(cmd, connection, null, SQLString, cmdParms);
12                 using (OracleDataAdapter da = new OracleDataAdapter(cmd))
13                 {
14                     DataSet ds = new DataSet();
15                     try
16                     {
17                         da.Fill(ds, "ds");
18                         cmd.Parameters.Clear();
19                     }
20                     catch (System.Data.OracleClient.OracleException ex)
21                     {
22                         throw new Exception(ex.Message);
23                     }
24                     //没有数据返回，返回null
25                     if (ds.Tables[0].Rows.Count <= 0)
26                     {
27                         return null;
28                     }
29                     return ds;
30                 }
31             }
32         }

2.返回DataTable数据，若查询返回行数为零，返回null

 1         /// <summary>
 2         /// 执行查询语句，返回DataTable
 3         /// </summary>
 4         /// <param name="SQLString">查询语句</param>
 5         /// <returns>DataTable</returns>
 6         public static DataTable Query(string SQLString, params OracleParameter[] cmdParms)
 7         {
 8             using (OracleConnection connection = new OracleConnection(connectionString))
 9             {
10                 OracleCommand cmd = new OracleCommand();
11                 PrepareCommand(cmd, connection, null, SQLString, cmdParms);
12                 using (OracleDataAdapter da = new OracleDataAdapter(cmd))
13                 {
14                     DataTable dt = new DataTable();
15                     try
16                     {
17                         da.Fill(dt);
18                         cmd.Parameters.Clear();
19                     }
20                     catch (System.Data.OracleClient.OracleException ex)
21                     {
22                         throw new Exception(ex.Message);
23                     }
24                     //没有数据返回，返回null
25                     if (dt.Rows.Count <= 0)
26                     {
27                         return null;
28                     }
29                     return dt;
30                 }
31             }
32         }

PrepareCommand的实现(1和2中均有用到)

 1         /// <summary>
 2         /// 打开数据库连接，传递参数等前置处理
 3         /// </summary>
 4         /// <param name="cmd">OracleCommand</param>
 5         /// <param name="conn">数据库连接</param>
 6         /// <param name="trans">数据库事务</param>
 7         /// <param name="cmdText">SQL语句</param>
 8         /// <param name="cmdParms">传递的参数</param>
 9         private static void PrepareCommand(OracleCommand cmd, OracleConnection conn,
10         OracleTransaction trans, string cmdText, OracleParameter[] cmdParms)
11         {
12             if (conn.State != ConnectionState.Open)
13                 conn.Open();
14             cmd.Connection = conn;
15             cmd.CommandText = cmdText;
16             if (trans != null)
17                 cmd.Transaction = trans;
18             cmd.CommandType = CommandType.Text;
19             if (cmdParms != null)
20             {
21                 foreach (OracleParameter parm in cmdParms)
22                 {
23                     if (parm.Value == null)
24                     {
25                         parm.Value = DBNull.Value;
26                     }
27                     cmd.Parameters.Add(parm);
28                 }
29             }
30         }

应用场景

1.防止多次判断如：

if (dt == null || dt.Rows.Count <= 0) { return; }

只需写作

if (dt == null) { return; }

2.防止引用为null的数据引发异常：

this.dataGridView1.DataSource = dt;

//若dt返回数据行数为零,以下赋值会产生异常

this.dataGridView1.Rows[0].Selected = false;