de.ipcon.db.castor

Class MEXTransformerEvaluator

java.lang.Object

de.ipcon.db.castor.MEXTransformerEvaluator

All Implemented Interfaces:

MEXTransformerEvaluatorI

Direct Known Subclasses:

FulltextEvaluator, IdListEvaluator, PrefetchEvaluator, UnionEvaluator

public abstract class MEXTransformerEvaluator
extends java.lang.Object
implements MEXTransformerEvaluatorI

Abstract base class for MEX (Macro Expression) Evaluators used during query transformation.

MEXTransformerEvaluators are plugged into a MEXTransformer to handle specific custom tags or domain-specific language (DSL) extensions within a query string. They follow a "detect-and-replace" pattern to transform high-level metadata instructions into concrete database constraints.

Lifecycle & Workflow

1. Detection: The transformer iterates through registered evaluators calling canHandle(CharSequence).
2. Evaluation: If an evaluator claims responsibility, evaluate(CharSequence, MEXTransformer) is invoked.
3. Substitution: The raw tag (e.g. {Fulltext ...}) is replaced by the string returned by the evaluator.

Implementation Strategy

Implementations typically use Regular Expressions for parsing.

Constructor Summary

Constructors

Constructor and Description
MEXTransformerEvaluator(MEXPersistenceQueryResults _mexQR) Constructor for the evaluator.

Method Summary

Modifier and Type	Method and Description
abstract boolean	canHandle(java.lang.CharSequence s) Checks if the provided text segment matches the specific tag format handled by this implementation.
abstract java.lang.CharSequence	evaluate(java.lang.CharSequence s, MEXTransformer transformer) Performs the actual transformation of the MEX expression.

Methods inherited from class java.lang.Object

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

Constructor Detail

MEXTransformerEvaluator

public MEXTransformerEvaluator(MEXPersistenceQueryResults _mexQR)

Constructor for the evaluator.

Parameters:

_mexQR - The runtime context required for lookups and service access.

Method Detail

canHandle

public abstract boolean canHandle(java.lang.CharSequence s)

Checks if the provided text segment matches the specific tag format handled by this implementation.

Performance Note: This should be a lightweight check, ideally using Matcher.lookingAt() to avoid unnecessary full-string scans.

Parameters:

_s - The segment of the query wrapped in braces (e.g. "Fulltext matches ...").

Returns:

true if this evaluator can transform the given string.

evaluate

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

Performs the actual transformation of the MEX expression.

This method is responsible for:

• Parsing arguments from the expression.
• Accessing mexQR for external data if required.
• Handling errors via MEXParseException or MEXUnavailableException.

Specified by:

evaluate in interface MEXTransformerEvaluatorI

Parameters:

s - The raw expression string extracted from the query.

transformer - The parent transformer, useful for determining the "source" entity or accessing the original query context.

Returns:

The replacement string to be injected into the final query.

Throws:

MEXException - if syntax is invalid or required services are unavailable.