dtl

DBView<DataObj, ParamObj>::delete_iterator


Category: iterators	Component type: type

Description

DBView<DataObj, ParamObj>::delete_iterator is an Output Iterator that performs the deletion of objects of type DataObj from a particular DBView (and thus the database). The actual DataObj that the delete_iterator references specifies the parameters of what DataObj's to delete from the database. To specify more parameters to refine the delete, define a ParamObjandBPA in the underlying DBView. The delete_iterator generates the following SQL statement to delete records from the database: "DELETE FROM " + tablename_from_view + " WHERE " + "<field1_from_BCA>=(?) AND <field2_from_BCA>=(?) AND ... " + posfix_clause_from_view. (But see BuildSpecialQry for how to override this.) The first set of parameters in the WHERE clause from the BCA will be automatically bound to fields in the DataObj. These parameters are set automatically upon assignment to the delete_iterator. Any additional parameters in the postfix clause will be bound to the ParamObj. Note that all of the restrictions of an Output Iterator must be obeyed, including the restrictions on the ordering of operator* and operator++ operations.

Definition

Defined in the delete_iterator.h header file.

Example:

// Delete objects from the database via a delete_iterator

class Example
{
  public:                                // tablename.columnname:
	int exampleInt;                 // DB_EXAMPLE.INT_VALUE
	string exampleStr;              // DB_EXAMPLE.STRING_VALUE
	double exampleDouble;           // DB_EXAMPLE.DOUBLE_VALUE
	long exampleLong;               // DB_EXAMPLE.EXAMPLE_LONG
	TIMESTAMP_STRUCT exampleDate;   // DB_EXAMPLE.EXAMPLE_DATE

	Example(int exInt, const string &exStr, double exDouble, long exLong,
		const TIMESTAMP_STRUCT &exDate) :
	   exampleInt(exInt), exampleStr(exStr), exampleDouble(exDouble), exampleLong(exLong),
	   exampleDate(exDate)
	{ }

};

class BCAExampleObj
{
public:
	void operator()(BoundIOs &boundIOs, Example &rowbuf)
	{
		boundIOs["STRING_VALUE"] == rowbuf.exampleStr;
		boundIOs["EXAMPLE_DATE"] == rowbuf.exampleDate;
	}
};


// Delete rows matching the specified Example objects from the database
void DeleteData()
{
	// construct view
	DBView<Example>
	view("DB_EXAMPLE", BCAExampleObj());

	// build a deleter for the view

	// *** SQL Query Generated for this delete_iterator: ***
 	// "DELETE FROM DB_EXAMPLE WHERE EXAMPLE_DATE = (?) AND STRING_VALUE = (?) "
	
	DBView<Example>::delete_iterator exampleDeleter = view;

	Example deleteMe;

	// now set Example object indicating which rows we want to delete
	deleteMe.exampleStr = "Example";

	TIMESTAMP_STRUCT y2k = {2000, 1, 1, 0, 0, 0, 0};
	deleteMe.exampleDate = y2k;

	
	*exampleDeleter = deleteMe;

	// execute the delete
	exampleDeleter++;

	cout << exampleDeleter.GetLastCount() << " rows deleted!" << endl;

	// now can perform other deletes using the same delete iterator
	
	// now set Example object and params indicating which rows we want to delete

	TIMESTAMP_STRUCT today = {1999, 9, 29, 0, 0, 0, 0};
	*exampleDeleter = Example(3, "operator->()works", 0.0, 0, today);

	// execute the delete
	exampleDeleter++;

	cout << exampleDeleter.GetLastCount() << " rows deleted!" << endl;
}

Template parameters

Parameter	Description	Default
`DataObj`	The type of object that will be updated in the DBView. This object will be bound through use of the BCA to the appropriate columns in the database. The set of value types of an `DBView::update_iterator` consists of a single type, DataObj.
`ParamObj`	The type of object that will be used to specify the postfix parameters to the DBView.	DefaultParamObj<DataObj>

Model of

Output Iterator.

Type requirements

DataObj and ParamObj must each fulfill the following requirements:.

Be of a type that is not primitive or of type string.
Have a publicly accessible copy constructor (the default is OK).
Have a publicly accessible assignment operator (the default is OK).

Public base classes

DB_iterator<DataObj, ParamObj>, iterator<output_iterator_tag, DataObj>

Members

Member	Where defined	Description
`DBView::delete_iterator()`	`delete_iterator`	Default constructor.
`DBView::delete_iterator(DBView<DataObj, ParamObj> &view)`	`delete_iterator`	See below.
`DBView::delete_iterator(const DBView::delete_iterator&)`	Output Iterator	The copy constructor
`DBView::delete_iterator& operator=(const DBView delete_iterator&)`	Output Iterator	The assignment operator
`DBView::delete_iterator& operator*(), DBView::delete_iterator& operator=(const DataObj &data)`	Output Iterator	Proxy operators necessary to emulate it = data. Return this.
`DBView::delete_iterator& operator++()`	Output Iterator	Preincrement. Deletes all DataObj's matching the parameters specified by the DataObj referenced by the iterator (and meeting the postfix clause). See Note [1].
`const DBView::delete_iterator operator++(int)`	Output Iterator	Preincrement. Deletes all DataObj's matching the parameters specified by the DataObj referenced by the iterator (and meeting the postfix clause). See Note [1].
`void swap(DBView::delete_iterator &other)`	DBView::delete_iterator	See below.

New members

These members are not defined in the Output Iterator requirements or in DB_iterator<DataObj, ParamObj>, but are specific to DBView::delete_iterator.

Function	Description
`DBView::delete_iterator(DBView<DataObj, ParamObj> &view)`	Creates an delete_iterator which refers to view.
`void swap(DBView::delete_iterator &other)`	Swap *this with other.

Notes

[1] operator++() is the operation that actually applies the delete to the database via the DBView. Each DBView::delete_iterator internally owns a DBStmt object which is allocated and prepared when the underlying ODBC statement handle is first needed and not before. The handle is not opened until absolutely needed in order to make copying and assigning these iterators an inexpensive operation. The DBStmt is executed once on each call to operator++(), whether the prefix or postfix version.