dtl

variant_field


Category: utilities	Component type: type

Description

The variant_field class provides a mechanism to access data fields within a variant_row. variant_field is designed to hold values of arbitrary types. In addition variant_field provides the ability for users to cast values between types and assign values back to the variant_row that created a given variant object. 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_row, 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"];// For gcc will need to call get_string() method here





	// 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: 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