dtl

DBView<DataObj, ParamObj>::update_iterator


Category: iterators	Component type: type

Description

DBView<DataObj, ParamObj>::update_iterator is an Output Iterator that performs the updating of objects of type DataObj in a particular DBView (and thus the database). The actual DataObj that the update_iterator references is the new value that any records meeting the iterator's SQL query. The update_iterator generates this SQL query to perform the update as: "UPDATE " + tablename_from_view + "SET " + "<field1_fromBCA>=(?), <field2_fromBCA>=(?), ... " + posfix_clause_from_view. (But see BuildSpecialQry for how to override this.) The parameters in the SET clause from the BCAare automatically bound by the update_iteratorto the fields in the DataObj. These parameters are set automatically upon assignment to the update_iterator. All 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 update_iterator.h header file.

Example:

//Update objects in the database via an update_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["INT_VALUE"] == rowbuf.exampleInt;

		boundIOs["STRING_VALUE"] == rowbuf.exampleStr;

		boundIOs["DOUBLE_VALUE"] == rowbuf.exampleDouble;

		boundIOs["EXAMPLE_LONG"] == rowbuf.exampleLong;

		boundIOs["EXAMPLE_DATE"] == rowbuf.exampleDate;

	}

};



class ExampleParamObj

{

  public:

	int lowIntValue;

	int highIntValue;

	string strValue;

	TIMESTAMP_STRUCT dateValue;

};



class BPAParamObj

{

public:

	void operator()(BoundIOs &boundIOs, ExampleParamObj &paramObj)

	{

	  boundIOs[0] == paramObj.lowIntValue;

	  boundIOs[1] == paramObj.highIntValue;

	  boundIOs[2] == paramObj.strValue;

	  boundIOs[3] == paramObj.dateValue;

	}



};





// update Example object (with new values) meeting a query in the database

void UpdateData()

{ 

	// construct view

	DBView<Example, ExampleParamObj>

	   view("DB_EXAMPLE", BCAExampleObj(), 

	   "WHERE INT_VALUE BETWEEN (?) AND (?) AND "

	   "STRING_VALUE = (?) OR EXAMPLE_DATE = (?)", BPAParamObj());



	// build an updater for the view



	// *** SQL Query Generated for this update_iterator: ***

	// "UPDATE DB_EXAMPLE SET DOUBLE_VALUE = (?), EXAMPLE_DATE = (?), EXAMPLE_LONG = (?), INT_VALUE = (?), "

	// "STRING_VALUE = (?) WHERE INT_VALUE BETWEEN (?) AND (?) AND STRING_VALUE = (?) OR EXAMPLE_DATE = (?)"

	

	DBView<Example, ExampleParamObj>::update_iterator exampleUpdater = view;



	// set data fields we want to update to their desired values

	// exampleStr to "Updated" andsampleLong to 0

	Example updateMe;



	updateMe.exampleStr = "Updated";

	updateMe.exampleLong = 25;



	TIMESTAMP_STRUCT today = {2000, 9, 29, 0, 0, 0,0};



	updateMe = Example(2121, "Updated", 99.99, 25, today);



	// now set the parameters indicating which rows

	// we want the update applied

	exampleUpdater.Params().lowIntValue = 5;

	exampleUpdater.Params().highIntValue = 13;

	exampleUpdater.Params().strValue = "FindMe";



	TIMESTAMP_STRUCT paramDate = {1999, 11, 11, 0,0, 0, 0};

	exampleUpdater.Params().dateValue = paramDate;



	// execute the update

	*exampleUpdater = updateMe;

	exampleUpdater++;



	cout << exampleUpdater.GetLastCount() << " rows updated!" << endl;



	// now can perform other updates using the same updater object

	// make sure to put in your new values for both the data and parameter values

	// for the update

	// set data fields we want to update to their desired values

	// exampleStr to "Second Update" and exampleLong to 66

	TIMESTAMP_STRUCT tomorrow = {2000, 9, 30, 0, 0,0, 0};



	updateMe = Example(2222, "Second Update", 0.11111, 66, tomorrow);



	// now set the parameters indicating which rows

	// we want the update applied

	exampleUpdater.Params().lowIntValue = 21;

	exampleUpdater.Params().highIntValue = 30;

	exampleUpdater.Params().strValue = "To find";



	TIMESTAMP_STRUCT otherParamDate = {2001, 10, 31, 0, 0, 0, 0};

	exampleUpdater.Params().dateValue = otherParamDate;



	// execute the update

	*exampleUpdater = updateMe;

	exampleUpdater++;



	cout << exampleUpdater.GetLastCount() << " rows updated!" << 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::update_iterator()`	`update_iterator`	Default constructor.
`DBView::update_iterator(DBView<DataObj, ParamObj> &view, bool bPrepare = true)`	`update_iterator`	See below.
`DBView::update_iterator(const DBView::update_iterator&)`	Output Iterator	The copy constructor
`DBView::update_iterator& operator=(const DBView update_iterator&)`	Output Iterator	The assignment operator
`DBView::update_iterator& operator*()`	Output Iterator	Proxy operators necessary to emulate it = data. Return this.
`DBView::update_iterator& operator*(), DBView::update_iterator& operator=(const DataObj &data)`	Output Iterator	Proxy operators necessary to emulate it = data. Updates all DataObj's meeting the iterator's SQL query to the new value specified in the DataObj to the DBView. Return this. See Note [1].
`DBView::update_iterator& operator++()`	Output Iterator	Preincrement.
`const DBView::update_iterator operator++(int)`	Output Iterator	Postincrement.
`void swap(DBView::update_iterator &other)`	DBView::update_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::update_iterator.

Function	Description
`DBView::update_iterator(DBView<DataObj, ParamObj> &view, bool bPrepare = true)`	Creates an update_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::update_iterator &other)`	Swap *this with other.

Notes

[1] operator=() is the operation that actually applies the update to the database via the DBView. Each DBView::update_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 versions of DTL wrote out to the database on operator++().