dtl

BoundIO and BoundIOs

Category: utilities	Component type: type

Description

A BoundIO is an object used to hold an association between a field in a query and a field in a user defined data object. The BoundIO class is held in a private member of the DBView template called the BoundIOs object which is an STL map<string, BoundIO> that holds a set of BoundIO objects that are mapped by SQL field name. As an end user, the four places you will encouter a BoundIO are when writing BCA , BPA, InsVal or SelVal functions.

Definition

Defined in the BoundIO.h header file.

Refinement of

None.

Associated types

NullField - a tag struct which indicates we want to set a field to null.

Example 1:

// Functor to bind SQL columns to a data object
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
};

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;
	}
};

Example 2:

//BPA Functor to bind SQL parameters to a data object

// "Example" class to hold rows from our database table
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)
	{ }

};

// Create an association between table columns and fields in our object
class BCAExampleObj
{
public:
	void operator()(BoundIOs &cols, Example &rowbuf)
    	{
	   cols["INT_VALUE"] >> rowbuf.exampleInt;
	   cols["STRING_VALUE"] >> rowbuf.exampleStr;
	   cols["DOUBLE_VALUE"] >> rowbuf.exampleDouble;
	   cols["EXAMPLE_LONG"] >> rowbuf.exampleLong;
	   cols["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;
	}

};

// read some Example objects from the database and return a vector of
// the results, use BPA to set join parameters
vector<Example> ReadData()
{
	vector<Example> results;

	// construct view
	
	DBView<Example, ExampleParamObj>
		view("DB_EXAMPLE", BCAExampleObj(),
		"WHERE INT_VALUE BETWEEN (?) AND (?) AND "
		"STRING_VALUE = (?) OR EXAMPLE_DATE < (?) ORDER BY EXAMPLE_LONG",
		BPAParamObj());

	// loop through query results and add them to our vector
	// in this loop, read_it.GetLastCount() records read from DB

	DBView<Example, ExampleParamObj>::select_iterator read_it = view.begin();

	// set parameter values for the WHERE clause in our SQL query
	read_it.Params().lowIntValue = 2;
	read_it.Params().highIntValue = 8;
	read_it.Params().strValue = "Example";
	
	TIMESTAMP_STRUCT paramDate = {2000, 1, 1, 0, 0, 0, 0};
	read_it.Params().dateValue = paramDate;

	for ( ; read_it != view.end();  read_it++)
	{
		cout << "Reading element #" << read_it.GetLastCount() << endl;
		results.push_back(*read_it);

		cout << "read_it->exampleInt = " << read_it->exampleInt << endl;
		cout << "read_it->exampleStr = " << read_it->exampleStr << endl;
		
	}
	
	return results;
}

Example 3:

//Default SelVal function to make sure fields in a row selected from the database are valid

// Default select validation behavior ... data is valid if and only if
// there are no columns which are null.
// If there are other checks you wish to make, put them in
// your own SelVal functor.
// You can also specialize this template if you wish to have different default behavior
// for your data class.
template<class DataObj> class DefaultSelValidate {
public:
bool operator()(BoundIOs &boundIOs, DataObj &rowbuf)
{
	for (BoundIOs::iterator b_it = boundIOs.begin();
				b_it != boundIOs.end(); b_it++)
	{
		BoundIO &boundIO = (*b_it).second;
		if (boundIO.IsColumn() && boundIO.IsNull())
			return false;  // found null column ... data is invalid
	}

	return true;	// no nulls found ... data is OK
}
};

Public base classes: BoundIO

None.

Public base classes: BoundIOs

map<string, BoundIO>

Notation:

Expression semantics: BoundIO

X a()

X a(constX &b)

X& operator=(const X&b)

bool IsColumn()

bool IsParam()

bool IsNull()

Expression semantics: BoundIOs

As per STL map but with the following modifications:

BoundIO &operator[](unsigned int paramNum)

BoundIO &operator[](const string &colName)

Notes

[1] Supported C++ types for binding to fields in a database:

Supported C++ data types and mappings (see ETI_Map::build() in bind_basics.cpp for details)

[2] If you are only using this BCA/BPA with a DBView template then the field you are binding to can be either statically or dynamically allocated by the DataObj, as long as the object has a correct copy and assigment operator for copying the field. If you want to use an IndexedDBView with your BCA, then the field must be a statically allocated member of the DataObj. The reason for this is that IndexedDBView computes a relative fieldoffset via &(rowbuf.Field) - &rowbuf that it uses for comparison functions for automatic indexing and update routines in the IndexedDBView. This kind of offset logic is only valid if the field is not dynamically allocated via operator new() or malloc(). So, if you want to use IndexedDBView we recommend that your fields be statically allocated members. (In fact, there is a complicated way around this restriction if you allocate your fields as a contiguous block. You can check out DynamicRowBCA in DynaDBView.h and the data_ptr() function that we define for the variant_row class in variant_row.h for an example of how we worked around this to accomodate dynamically sized rows. The result is not for the faint of heart.) Here is an example of what we are talking about:

#define DYNAMIC_SIZE 100 
class BCADynamicObj;
class Dynamic {
	char **szDynamicString;

public:

	Dynamic() {
		szDynamicString = (char **)malloc(DYNAMIC_SIZE);
	}

	Dynamic(const Dynamic &other) {
		szDynamicString = (char **)malloc(DYNAMIC_SIZE);	
		memcpy(szDynamicString, other.szDynamicString, DYNAMIC_SIZE);
	}

	const Dynamic & operator=(const Dynamic &other) {
		if (this != &other) {
			if (szDynamicString == NULL)
				szDynamicString = (char **)malloc(DYNAMIC_SIZE);	
			memcpy(szDynamicString, other.szDynamicString, DYNAMIC_SIZE);
		}

	}
	

	~Dynamic() {
		if (szDynamicString != NULL)
			free(szDynamicString);
	}

	friend class BCADynamicObj;
};

// This BCA will work with DBView but not IndexedDBView because szDynamicString is dynamic
class BCADynamicObj
{
public:
	void operator()(BoundIOs &boundIOs, Dynamic &rowbuf)
    	{
	   boundIOs["STRING_VALUE"] == *(rowbuf.szDynamicString);
	}
};

See also

BPA, BCA, InsVal, SelVal, DBView, IndexedDBView

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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