Expression Classes

DB Interface Module Reference Guide
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2.6 Expression Classes

Class RWDBExpr is a base class for a family of classes that allow you to program SQL expressions in C++. Additional classes in this category include RWDBAssignment, RWDBCriterion, RWDBCollectableExpr, RWDBBoundExpr, and RWDBJoinExpr. Chapter 5 of the DB Interface Module User's Guide contains examples of using these classes.

The DB Interface Module also provides an extensible mechanism for defining SQL expressions for your specific needs. The classes RWDBExprFormDefinition, RWDBExprFuncDef{n}, RWDBCritFormDefinition, and RWDBCritFuncDef{n} support this mechanism. For detailed information on any class, see its entry in this Reference Guide.

Table 5 lists and briefly describes the Expression Classes.

Table 5: The Expression Classes

Class Name	Description
*RWDBExpr*	Codes SQL expressions using C++ syntax
*RWDBAssignment*	Represents the SQL `Set x = y` phrase
*RWDBCriterion*	Represents an SQL expression evaluated as a boolean
*RWDBCollectableExpr*	SQL expression that can be placed in an *RWCollection*
*RWDBBoundExpr*	Represents a placeholder in dynamic SQL statements
*RWDBJoinExpr*	Defines SQL `JOIN` expressions for ANSI-compliant servers
*RWDBExprFormDefinition*	Defines SQL expressions using replacement text
*RWDBExprFuncDef{n}*	Defines SQL functions with `n` arguments
*RWDBCritFormDefinition*	Defines boolean SQL expressions using replacement text
*RWDBCritFuncDef{n}*	Defines boolean SQL expressions with `n` arguments

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