SourcePro® 2024.1 |
SourcePro® API Reference Guide |
Base class for a family of classes that defines functional notation for RWDBExpr. More...
#include <rw/db/func.h>
Public Member Functions | |
RWDBExprFormDefinition () | |
RWDBExprFormDefinition (const RWCString &formatString) | |
virtual RWDBExpr | operator() () |
virtual RWDBExpr | operator() (const RWDBExpr &expr0) |
virtual RWDBExpr | operator() (const RWDBExpr &expr0, const RWDBExpr &expr1) |
virtual RWDBExpr | operator() (const RWDBExpr &expr0, const RWDBExpr &expr1, const RWDBExpr &expr2) |
virtual RWDBExpr | operator() (const RWDBExpr &expr0, const RWDBExpr &expr1, const RWDBExpr &expr2, const RWDBExpr &expr3) |
RWDBExprFormDefinition is a base class for a family of classes that provide an extensible mechanism for an application to define functional notation for RWDBExpr. RWDBExprFormDefinition allows the creation an object that translates into an RWDBExpr and can eventually be expanded into an SQL string. The object will allow up to four expressions to be embedded into the resultant string.
An RWDBExprFormDefinition 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 this way may subsequently be referenced like predefined functions, such as rwdbMax and rwdbAvg.
When an RWDBExprFormDefinition object is expanded by the asString() method of RWDBExpr, 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. There can be multiple instances of a placeholder 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 RWDBExprFuncDef0, RWDBExprFuncDef1, RWDBExprFuncDef2, RWDBExprFuncDef3 and RWDBExprFuncDef4 classes.
RWDBCritFormDefinition provides a parallel mechanism for defining an RWDBCriterion, rather than using RWDBExpr.
RWDBExprFuncDef0, RWDBExprFuncDef1, RWDBExprFuncDef2, RWDBExprFuncDef3, and RWDBExprFuncDef4 are derived from RWDBExprFormDefinition. They provide a simplified interface for functions requiring 0
- 4
parameters, respectively, and do not require positional placeholders.
See RWDBExpr for details on SQL expressions in the DB Interface Module, as well as for a complete listing of predefined SQL functions.
Imagine that a database vendor's SQL variant provides the function DECRYPT(string, length, key)
. The DB Interface Module has no direct support for this function, yet we would like to use it without losing the benefits of its high-level constructs for data manipulation. To do so, we can use a function which we define ourselves:
Note that the number of parameters actually passed to decrypt
is not checked. Compare this example with the RWDBExprFuncDef3 example to see how such checking can be enabled.
RWDBExprFormDefinition::RWDBExprFormDefinition | ( | ) |
Creates an empty RWDBExprFormDefinition. Provided for convenience only.
RWDBExprFormDefinition::RWDBExprFormDefinition | ( | const RWCString & | formatString | ) |
Creates an RWDBExprFormDefinition with the given formatString. Objects instantiated this way may subsequently be referenced as though they were predefined SQL functions.
|
virtual |
Returns an RWDBExpr that encapsulates the formatString
associated with RWDBExprFormDefinition.
Reimplemented in RWDBExprFuncDef0, RWDBExprFuncDef1, RWDBExprFuncDef2, RWDBExprFuncDef3, and RWDBExprFuncDef4.
Returns an RWDBExpr that can replace any instance of %0
in self's function definition with expr0.
Reimplemented in RWDBExprFuncDef0, RWDBExprFuncDef1, RWDBExprFuncDef2, RWDBExprFuncDef3, and RWDBExprFuncDef4.
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virtual |
Returns an RWDBExpr that can replace any instance of %0
in self's function definition with expr0 and %1
with expr1.
Reimplemented in RWDBExprFuncDef0, RWDBExprFuncDef1, RWDBExprFuncDef2, RWDBExprFuncDef3, and RWDBExprFuncDef4.
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virtual |
Returns an RWDBExpr that can replace any instance of %0
in self's function definition with expr0, %1
with expr1, and so on.
Reimplemented in RWDBExprFuncDef0, RWDBExprFuncDef1, RWDBExprFuncDef2, RWDBExprFuncDef3, and RWDBExprFuncDef4.
|
virtual |
Returns an RWDBExpr that can replace any instance of %0
in self's function definition with expr0, %1
with expr1, and so on.
Reimplemented in RWDBExprFuncDef0, RWDBExprFuncDef1, RWDBExprFuncDef2, RWDBExprFuncDef3, and RWDBExprFuncDef4.
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