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* Licensed under the Apache License, Version 2.0 (the "License");
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* database integrations.
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package org.jooq;
import java.sql.PreparedStatement;
import java.util.EventListener;
/**
* A listener for {@link QueryPart} traversal events.
* <p>
* Users may want to centrally inject custom behaviour when rendering their
* {@link QueryPart} objects or when binding values to {@link PreparedStatement}
* s. This service provider allows to hook in callback method implementations
* before or after these events:
* <ul>
* <li>The visit of a {@link Clause}</li>
* <li>The visit of a {@link QueryPart}</li>
* </ul>
* <p>
* The following rules apply to visiting clauses and query parts:
* <ul>
* <li>Clauses may "surround" a query part. See an example below.</li>
* <li>Not every query part is "surrounded" by a clause</li>
* </ul>
* <p>
* An example is given here:
* <code><pre>SELECT 1 FROM [A CROSS JOIN B]</pre></code>
* <p>
* The above example will create the following set of events:
*
* <pre>
* {@link Clause#SELECT}
* +-{@link Clause#SELECT_SELECT}
* | +-{@link Clause#FIELD}
* | +-val(1)
* +-{@link Clause#SELECT_FROM}
* +-{@link Clause#TABLE_JOIN}
* +-{@link Clause#TABLE}
* | +-table("A")
* +-{@link Clause#TABLE_JOIN_CROSS}
* +-{@link Clause#TABLE}
* +-table("B")
* </pre>
* <p>
* Whatever is not a {@link Clause} in the above example is a {@link QueryPart}.
* <p>
* <h3>A remark about performance</h3>
* <p>
* Implementors of this SPI should be wary of performance implications of their
* implementations. The below methods are called for every AST element of every
* query, which produces a lot of calls throughout an application. What would
* otherwise be premature optimisations may have great effect inside the
* <code>VisitListener</code>. For more details, please refer to this article:
* <a href=
* "http://blog.jooq.org/2015/02/05/top-10-easy-performance-optimisations-in-java/">
* http://blog.jooq.org/2015/02/05/top-10-easy-performance-optimisations-in-
* java/</a>.
*
* @author Lukas Eder
*/
public interface VisitListener extends EventListener {
/**
* Called before entering a {@link Clause}.
*
* @see Context#start(Clause)
*/
void clauseStart(VisitContext context);
/**
* Called after leaving a {@link Clause}.
*
* @see Context#end(Clause)
*/
void clauseEnd(VisitContext context);
/**
* Called before visiting a {@link QueryPart}.
* <p>
* Certain <code>VisitListener</code> implementations may chose to replace
* the {@link QueryPart} contained in the argument {@link VisitContext}
* through {@link VisitContext#queryPart(QueryPart)}. This can be used for
* many use-cases, for example to add a <code>CHECK OPTION</code> to an
* Oracle <code>INSERT</code> statement: <code><pre>
* -- Original query
* INSERT INTO book (id, author_id, title)
* VALUES (10, 15, '1984')
*
* -- Transformed query
* INSERT INTO (
* SELECT * FROM book
* WHERE author_id IN (1, 2, 3)
* WITH CHECK OPTION
* ) (id, author_id, title)
* VALUES (10, 15, '1984')
* </pre></code> The above SQL transformation allows to prevent inserting
* new books for authors other than those with
* <code>author_id IN (1, 2, 3)</code>
*
* @see Context#visit(QueryPart)
*/
void visitStart(VisitContext context);
/**
* Called after visiting a {@link QueryPart}.
*
* @see Context#visit(QueryPart)
*/
void visitEnd(VisitContext context);
}