de.ipcon.db.castor

Class UnionEvaluator

java.lang.Object

de.ipcon.db.castor.MEXTransformerEvaluator

de.ipcon.db.castor.UnionEvaluator

All Implemented Interfaces:

MEXTransformerEvaluatorI

public class UnionEvaluator
extends MEXTransformerEvaluator

MEXTransformerEvaluator class responsible for handling "Union" and "UnionAll" expressions within a MEX (Metadata Expression) template.

Unlike list-based evaluators that return text to be inserted into a query, this evaluator interacts directly with the MEXPersistenceQueryResults context to register supplementary queries. These queries are executed and their results are merged according to the specified set operation.

Example usage: "{Union SELECT o.id FROM Order o WHERE o.Status = 'active'}" "{UnionAll @customHandler SELECT p.id FROM Person p}"

Constructor Summary

Constructors

Constructor and Description
UnionEvaluator(MEXPersistenceQueryResults _mexQR) Constructs a new UnionEvaluator.

Method Summary

Modifier and Type	Method and Description
boolean	canHandle(java.lang.CharSequence s) Determines if the expression is a Union operation.
java.lang.CharSequence	evaluate(java.lang.CharSequence s, MEXTransformer transformer) Evaluates the Union expression by spawning a new QueryHandler and adding it to the parent MEX context.
java.lang.String[]	getGroups(java.lang.CharSequence s) Extracts the query components from the expression.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

UnionEvaluator

public UnionEvaluator(MEXPersistenceQueryResults _mexQR)

Constructs a new UnionEvaluator.

Parameters:

_mexQR - the MEX query results context where sub-queries will be registered.

Method Detail

canHandle

public boolean canHandle(java.lang.CharSequence s)

Determines if the expression is a Union operation.

Specified by:

canHandle in class MEXTransformerEvaluator

Parameters:

s - the expression string to check.

Returns:

true if it begins with Union or UnionAll.

getGroups

public java.lang.String[] getGroups(java.lang.CharSequence s)
                             throws MEXParseException

Extracts the query components from the expression.

Parameters:

s - the raw instruction sequence.

Returns:

A String array where index 0 is the OQL query and index 1 is the handler alias (may be null).

Throws:

MEXParseException - if the syntax does not match the expected pattern.

evaluate

public java.lang.CharSequence evaluate(java.lang.CharSequence s,
                                       MEXTransformer transformer)

Evaluates the Union expression by spawning a new QueryHandler and adding it to the parent MEX context.

This method returns an empty string because the "Union" operation does not modify the text of the primary query; instead, it registers a side-car query that is managed by the mexQR logic.

Specified by:

evaluate in interface MEXTransformerEvaluatorI

Specified by:

evaluate in class MEXTransformerEvaluator

Parameters:

s - the instruction sequence.

transformer - the active transformer.

Returns:

an empty CharSequence as the query is handled via context registration.

Throws:

java.lang.IllegalArgumentException - if the sub-query initialization fails (e.g. bad OQL syntax).