Prevents duplicate logic judgments or throws exceptions caused by zero returned data behavior when querying data.

Prevents duplicate logic judgments or throws exceptions caused by zero returned data behavior when querying data.

The following code uses the ORACLE database as an example:

1. DataSet data is returned. If the number of returned rows is zero, null is returned.

1 // <summary> 2 // execute the query statement, return DataSet 3 /// </summary> 4 /// <param name = "SQLString"> query statement </param> 5 /// <returns> DataSet </returns> 6 public static DataSet Query (string SQLString, params OracleParameter [] partition parms) 7 {8 using (OracleConnection connection = new OracleConnection (connectionString) 9 {10 OracleCommand cmd = new OracleCommand (); 11 PrepareCommand (cmd, connection, null, SQLString, partition parms); 12 using (OracleDataAdapter da = new OracleDataAdapter (cmd) 13 {14 DataSet ds = new DataSet (); 15 try16 {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 // No data is returned. null25 if (ds. Tables [0]. Rows. Count <= 0) 26 {27 return null; 28} is returned}29 return ds; 30} 31} 32}

2. DataTable data is returned. If the number of rows returned by the query is zero, null is returned.

1 // <summary> 2 // execute the query statement, return DataTable 3 /// </summary> 4 /// <param name = "SQLString"> query statement </param> 5 /// <returns> DataTable </returns> 6 public static DataTable Query (string SQLString, params OracleParameter [] partition parms) 7 {8 using (OracleConnection connection = new OracleConnection (connectionString) 9 {10 OracleCommand cmd = new OracleCommand (); 11 PrepareCommand (cmd, connection, null, SQLString, partition parms); 12 using (OracleDataAdapter da = new OracleDataAdapter (cmd) 13 {14 DataTable dt = new DataTable (); 15 try16 {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 // No data is returned. null25 if (dt. Rows. Count <= 0) 26 {27 return null; 28} is returned}29 return dt; 30} 31} 32}

Implementation of PrepareCommand (useful in both 1 and 2)

1 // <summary> 2 // open the database connection, PASS Parameters and other pre-processing 3 /// </summary> 4 /// <param name = "cmd"> OracleCommand </param> 5 /// <param name = "conn "> database connection </param> 6 // <param name =" trans "> database transactions </param> 7 /// <param name =" plain text "> SQL statement </param> 8 // <param name = "param parms"> passed parameter </param> 9 private static void PrepareCommand (OracleCommand cmd, oracleConnection conn, 10 OracleTransaction trans, string plain text, OracleParame Ter [] parms) 11 {12 if (conn. State! = ConnectionState. Open) 13 conn. Open (); 14 cmd. Connection = conn; 15 cmd. CommandText = plain text; 16 if (trans! = Null) 17 cmd. Transaction = trans; 18 cmd. CommandType = CommandType. Text; 19 if (partition parms! = Null) 20 {21 foreach (OracleParameter parm in parallel parms) 22 {23 if (parm. value = null) 24 {25 parm. value = DBNull. value; 26} 27 cmd. parameters. add (parm); 28} 29} 30}

 Application scenarios

1. prevent multiple judgments, such:

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

Write only

If (dt = null) {return ;}

2. prevent exceptions caused by null data reference:

This. Maid = dt;

// If the number of data rows returned by dt is zero, the following assignment will cause an exception.

This. Maid [0]. Selected = false;