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"];

	// 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