dtl

variant_row


Category: utilities	Component type: type

Description

The variant_row class provides a mechanism to hold an arbitrary number of fields with values of arbitrary types. This class is used primarily by dynamic queries where the number and the types of the fields returned by a query are unknown.

Definition

Defined in the variant_row.h header file.

Refinement of

None.

Associated types

variant_field, TypeTranslation.

Example 1:

// Manipulating fields in a variant_row



void variant_row_example(void) {



	TIMESTAMP_STRUCT test_date = {1999, 9, 29, 0, 0, 0, 0};



	vector<TypeTranslation> types;

	vector<string> names;

	int i;

	string s;

	TypeTranslation vt0=TypeTranslation(typeid(int).name(), C_INT, SQL_INTEGER, SQL_C_SLONG,

				TypeTranslation::TYPE_PRIMITIVE, sizeof(int)), 

			vt1=TypeTranslation(typeid(string).name(), C_STRING, SQL_VARCHAR, SQL_C_CHAR,

				TypeTranslation::TYPE_COMPLEX, sizeof(string));



	types.push_back(vt0);

	names.push_back("int");



	types.push_back(vt1);

	names.push_back("string");



	variant_row r(types, names);

	

	

	r["int"] = (int)r["int"] + 5;

	i = (int)r["int"];

	

	s = (string) r["int"];



	r["int"] = test_date;

	s = (string) r["int"];



	// Print out the column names

	vector<string> colNames = r.GetNames();

	for (vector<string>::iterator name_it = colNames.begin(); name_it != colNames.end(); name_it++)

	{

		cout << (*name_it) << " ";

	}

	cout << endl;



	// Print out all column values

	for (i = 0; i < r.size(); i++)

		cout << r[i] << " ";

	cout << endl;





};

Example 2:

Example: Reading a set of records from an Oracle stored procedure.



// Oracle stored procedure we wish to test

// for more information on this example, see the following Oracle documentation

#if 0

 Create or replace package ExampleInfo as



   Type ExampleRec is record



   (

   INT_VALUE     integer,



   STRING_VALUE   varchar2(50)



   );



   Type ExampleCursor is ref cursor return 



   ExampleRec;



   End ExampleInfo;



   



   Create or replace procedure ExampleInfoProc



   (LONG_CRITERIA IN integer, empcursor IN OUT 



   ExampleInfo.ExampleCursor)



   As



   Begin



   Open empcursor For



   select INT_VALUE, STRING_VALUE 



   from db_example



   where EXAMPLE_LONG = LONG_CRITERIA;



   End;

#endif



class ProcBCA {

public:

 void operator()(BoundIOs &cols, variant_row &row)

 {

  cols["INT_VALUE"] >> row._int();

  cols["STRING_VALUE"] >> row._string();

  

  cols.BindVariantRow(row);

 }

};



class ProcParams {

public:

	long long_criteria;

};



class ProcBPA {

public:

 void operator()(BoundIOs &cols, ProcParams &row)

 {

  cols[0] << row.long_criteria;

 }

};



// Read the contents of a table and print the resulting rows

// *** you must have Oracle ODBC driver version 8.1.5.3.0 for this to work ***

// The reason why is that the stored procedure shown above returns a "cursor"

// to pass back multiple rows which is only supported in Oracle ODBC driver

// version 8.1.5.3.0 or higher.  (Merant drivers for Oracle also support this syntax.)

void StoredProcReadData() {



        // Note: ExampleInfoProc takes an integer as an input parameter to determine

        // what records to return, and returns a cursor to a set of rows as an

        // output parameter. The output cursor is bound implicitly as a set of columns.

	DBView<variant_row, ProcParams> view("{call ExampleInfoProc(?)}", 

		ProcBCA(), "", ProcBPA());



	variant_row s(view.GetDataObj());



	// Print out the column names

	vector<string> colNames = s.GetNames();

	for (vector<string>::iterator name_it = colNames.begin(); name_it != colNames.end(); ++name_it)

		cout << (*name_it) << " ";

	cout << endl;



	// Print out all rows and columns from our query

	DBView<variant_row, ProcParams>::sql_iterator print_it = view.begin();

	print_it.Params().long_criteria = 22;



	for (; print_it != view.end(); ++print_it)

	{

		 variant_row r = *print_it;

		 for (size_t i = 0; i < r.size(); ++i)

		 	cout << r[i] << " ";

		 cout << endl;

	}

}

Example 3:

Example: Using a DynamicDBView to insert records into the database. Illustrates writing NULL values to the database.

// Using a DynamicDBView to insert records into the database.



// this example also shows how to set NULL fields in a variant_row



// Insert two rows into a table with unknown fields

void SimpleDynamicWrite() {

	TIMESTAMP_STRUCT paramDate = {2012, 12, 23, 0, 0, 0, 0}; 

	// Mayan DOOMSDAY! End of the Mayan 5126 year long calendar cycle starting from May 1, 3094 B.C.

	// Date is 13.13.13.0.0.0.0  4 Ahaw, 3 K'ank'in

	

	DynamicDBView<> view("DB_EXAMPLE", "*");



	DynamicDBView<>::insert_iterator write_it = view;



	// NOTE: We need to construct r from the view itself since we

	// don't know what fields the table will contain.

	// We therefore make a call to the DataObj() function to have the

	// table return us a template row with the correct number of fields

	// and field types.

	variant_row r(view.GetDataObj());



	// Prepare the number of the beast!

	// Set all fields to the value 6,

	// except for the last column which is a date and cannot

	// currently accept numeric values

	for (size_t i = 0; i < r.size()-1; i++)

	{

		 r[i] = 6;

	}

	r[i] = paramDate;  // set the Doomsdate



	// insert the number

	*write_it = r;

	write_it++;



	// Prepare the number of angels who stand before

	// the throne of God!

	// Set all fields to the value 7,

	// except for the last column which is a date and cannot

	// currently accept numeric values

	for (i = 0; i < r.size()-1; i++)

	{

		 r[i] = 7;

	}

	r[i] = paramDate;



	// insert the number

	*write_it = r;

	write_it++;



	// Insert Purgatory (the void) into the database.

	// Set all fields to NULL

	for (i = 0; i < r.size()-1; i++)

	{

		 r[i] = NullField();

	}

	r[i] = NullField();



	// insert the number

	*write_it = r;

	write_it++;



	// For more on this example - see the *REAL* DTL homepage!

}

Public base classes