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 ParamObj and BPA 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;



	// execute the delete

	*exampleDeleter = deleteMe;

	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};



	// execute the delete

	*exampleDeleter = Example(3, "operator->()works", 0.0, 0, today);

	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:.

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, bool bPrepare = true) 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*() Output Iterator Proxy operator necessary to emulate *it = data. Return *this.
DBView::delete_iterator& operator=(const DataObj &data) Output Iterator Proxy operator necessary to emulate *it = data. Deletes all DataObj's matching the parameters specified by the DataObj referenced by the iterator (and meeting the postfix clause). Return *this. See Note [1].
DBView::delete_iterator& operator++() Output Iterator Preincrement.
const DBView::delete_iterator operator++(int) Output Iterator Preincrement.
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, bool bPrepare = true) Creates an delete_iterator which refers to view. Set bPrepare to true if you want the iterator to use SQLPrepare() and SQLExecute() in the event you are executing the statement many times. Otherwise, the iterator will use SQLExecDirect().
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=(). Note that previous DTL versions committed on operator++().

See also

DB_iterator, Output Iterator, Input Iterator.


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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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