dtl

DynamicDBView <ParamObj>

Category: containers	Component type: type

Description

The DynamicDBView container is a refinement of DBView used for queries where the number and types of the fields in the query is unknown until runtime. DynamicDBView specialises the DBView template to use a variant_row object to hold rows from the query. The variant_row object provides a mechanism to hold an arbitrary number of fields with values of arbitrary types. Individual fields within the row are accessed by using methods from the variant_row object. Note that if the view uses autokeys that the autokey will become part of the variant_row objects returned in the view.

Refinement of

DBView.

Associated types

None, except for those defined by DBView.

Example 1:

// Using a DynamicDBView to read rows from the database.

// Read the contents of a table and print the resulting rows
void SimpleDynamicRead() {

	// Our query will be "SELECT * FROM DB_EXAMPLE"
	DynamicDBView<> view("DB_EXAMPLE", "*");

	// 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.
	// We use this construction since we can't be guaranteed that the table
	// is non-empty & we want to still display column names in this case.
	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
	DynamicDBView<>::select_iterator print_it = view.begin();
	for (print_it = view.begin(); 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 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

DBView<variant_row, ParamObj>

Template parameters

Notation

Expression semantics

DynamicDBView(const string &tableList, 
const string &fieldList,
const string postfix = "", 
const BPA bpa_functor = DefaultBPA<ParamObj>(),
const SelVal sel_val = DefaultSelVal<variant_row>(),
const InsVal ins_val = DefaultInsVal<variant_row>(),
const IOHandler<variant_row, ParamObj> io_hand = DEFAULT_IO_HANDLER<variant_row, ParamObj>(),
DBConnection &connection = DBConnection::GetDefaultConnection(),
const KeyMode km = USE_AUTO_KEY, const string &keyList = "")

Members

As per DBView with the following changes.

DynamicDBView(const string &tableList, 
const string &fieldList,
const string &postfix = "", 
const BPA bpa_functor = DefaultBPA<ParamObj>(),
const SelVal sel_val = DefaultSelVal<variant_row>(),
const InsVal ins_val = DefaultInsVal<variant_row>(),
const IOHandler<variant_row, ParamObj> io_hand = DEFAULT_IO_HANDLER<variant_row, ParamObj>(),
DBConnection &connection = DBConnection::GetDefaultConnection(), const KeyMode km = USE_AUTO_KEY,
const string &keyList = "")

See also

DBView, Associative Container, Multiple Associative Container, Unique Sorted Associative Container, Multiple Sorted Associative Container,

BPA, SelVal, InsVal, DBConnection

Copyright © 2002, Michael Gradman and Corwin Joy.

Permission to use, copy, modify, distribute and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appears in all copies and that both that copyright notice and this permission notice appear in supporting documentation. Corwin Joy and Michael Gradman make no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

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