RWDBCritFormDefinition Class Reference
[Expressions]

Base class for a family of classes used to define functional notation for RWDBCriterion. More...

#include <rw/db/func.h>

Inheritance diagram for RWDBCritFormDefinition:

List of all members.

Public Member Functions
	RWDBCritFormDefinition ()
	RWDBCritFormDefinition (const RWCString &formatString)
virtual RWDBCriterion	operator() ()
virtual RWDBCriterion	operator() (const RWDBExpr &expr0)
virtual RWDBCriterion	operator() (const RWDBExpr &expr0, const RWDBExpr &expr1)
virtual RWDBCriterion	operator() (const RWDBExpr &expr0, const RWDBExpr &expr1, const RWDBExpr &expr2)
virtual RWDBCriterion	operator() (const RWDBExpr &expr0, const RWDBExpr &expr1, const RWDBExpr &expr2, const RWDBExpr &expr3)

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Detailed Description

RWDBCritFormDefinition is a base class for a family of classes that provides an extensible mechanism an application can use to define functional notation for RWDBCriterion. RWDBCritFormDefinition creates an object that can translate into an RWDBCriterion and eventually be expanded into an SQL string. The object allows up to four expressions to be embedded into the resultant string.

An RWDBCritFormDefinition object is instantiated with a format string. The format string may contain placeholders for up to four positional parameters, which are labeled %0 through %3. An object defined in this way may subsequently be referenced in the same way that predefined functions like rwdbMax and rwdbAvg are referenced.

When an RWDBCritFormDefinition object is expanded by the asString() method of an RWDBCriterion, each instance of %0 is replaced with the first actual parameter, each instance of %1 is replaced with the second actual parameter, and so on. Multiple instances of a placeholder can exist in the format string, and the placeholders may occur in any order. This allows great flexibility in defining functions, at the cost of losing compile-time checking on the number of parameters actually passed. To enable compile-time checking on the number of actual parameters, at the cost of some flexibility, use the RWDBCritFuncDef0, RWDBCritFuncDef1, RWDBCritFuncDef2, RWDBCritFuncDef3 and RWDBCritFuncDef4 classes.

Synopsis

 #include <rw/db/func.h>
 
 RWDBCritFormDefinition myFunc("myFormat");

Related Classes

RWDBExprFormDefinition provides a parallel mechanism for defining an RWDBExpr, rather than using an RWDBCriterion.

RWDBCritFuncDef0, RWDBCritFuncDef1, RWDBCritFuncDef2, RWDBCritFuncDef3, and RWDBCritFuncDef4 are derived from RWDBCritFormDefinition. They provide a simplified interface for functions requiring 0 - 4 parameters, respectively, and do not require positional placeholders.

See RWDBCriterion for details on SQL WHERE clauses in the DB Interface Module.

Examples

Imagine that a database vendor's SQL variant provides the boolean function VALID_NAME(string), which can be used in a WHERE clause. The DB Interface Module has no direct support for this function, yet we would like to use it without losing the benefits of high-level constructs for data manipulation. To do so, we can use a function which we define ourselves:

 RWDBCritFormDefinition validName("VALID_NAME(%0)");
 RWDBTable potentialNames = myDbase.table("potentialNames");
 RWDBColumn name = potentialNames["name"];
 RWDBSelector usableNames = myDbase.selector();
 usableNames << name;
 usableNames.where(validName(name));

Note that the number of parameters actually passed to validName is not checked. Compare this example with the RWDBCritFuncDef1 example to see how such checking can be enabled.

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Constructor & Destructor Documentation

RWDBCritFormDefinition::RWDBCritFormDefinition

(

)

The default constructor creates an empty RWDBCritFormDefinition.

RWDBCritFormDefinition::RWDBCritFormDefinition

(

const RWCString &

formatString

)

Creates an RWDBCritFormDefinition with the given formatString. Objects instantiated in this way may subsequently be referenced as though they were predefined SQL functions.

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Member Function Documentation

virtual RWDBCriterion RWDBCritFormDefinition::operator()	(	const RWDBExpr &	expr0,
		const RWDBExpr &	expr1,
		const RWDBExpr &	expr2,
		const RWDBExpr &	expr3
	)			[virtual]

Returns an RWDBCriterion with the ability to replace any instance of %0 in self's function definition with expr0, %1 with expr1, and so on.

Reimplemented in RWDBCritFuncDef0, RWDBCritFuncDef1, RWDBCritFuncDef2, RWDBCritFuncDef3, and RWDBCritFuncDef4.

virtual RWDBCriterion RWDBCritFormDefinition::operator()	(	const RWDBExpr &	expr0,
		const RWDBExpr &	expr1,
		const RWDBExpr &	expr2
	)			[virtual]

Returns an RWDBCriterion with the ability to replace any instance of %0 in self's function definition with expr0, %1 with expr1, and so on.

Reimplemented in RWDBCritFuncDef0, RWDBCritFuncDef1, RWDBCritFuncDef2, RWDBCritFuncDef3, and RWDBCritFuncDef4.

virtual RWDBCriterion RWDBCritFormDefinition::operator()	(	const RWDBExpr &	expr0,
		const RWDBExpr &	expr1
	)			[virtual]

Returns an RWDBCriterion with the ability to replace any instance of %0 in self's function definition with expr0 and %1 with expr1.

Reimplemented in RWDBCritFuncDef0, RWDBCritFuncDef1, RWDBCritFuncDef2, RWDBCritFuncDef3, and RWDBCritFuncDef4.

virtual RWDBCriterion RWDBCritFormDefinition::operator()

(

const RWDBExpr &

expr0

)

[virtual]

Returns an RWDBCriterion with the ability to replace any instance of %0 in self's function definition with expr0.

Reimplemented in RWDBCritFuncDef0, RWDBCritFuncDef1, RWDBCritFuncDef2, RWDBCritFuncDef3, and RWDBCritFuncDef4.

virtual RWDBCriterion RWDBCritFormDefinition::operator()

(

)

[virtual]

Returns an RWDBCriterion that encapsulates the formatString associated with RWDBCritFormDefinition.

Reimplemented in RWDBCritFuncDef0, RWDBCritFuncDef1, RWDBCritFuncDef2, RWDBCritFuncDef3, and RWDBCritFuncDef4.