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- All Superinterfaces:
EventListener
- All Known Implementing Classes:
DefaultVisitListener
public interface VisitListener extends EventListener
A listener forQueryPart
traversal events.Users may want to centrally inject custom behaviour when rendering their
QueryPart
objects or when binding values toPreparedStatement
s. This service provider allows to hook in callback method implementations before or after these events:The following rules apply to visiting clauses and query parts:
- Clauses may "surround" a query part. See an example below.
- Not every query part is "surrounded" by a clause
An example is given here:
SELECT 1 FROM [A CROSS JOIN B]
The above example will create the following set of events:
Clause.SELECT
+-Clause.SELECT_SELECT
| +-Clause.FIELD
| +-val(1) +-Clause.SELECT_FROM
+-Clause.TABLE_JOIN
+-Clause.TABLE
| +-table("A") +-Clause.TABLE_JOIN_CROSS
+-Clause.TABLE
+-table("B")Whatever is not a
Clause
in the above example is aQueryPart
.A remark about performance
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
VisitListener
. For more details, please refer to this article: http://blog.jooq.org/2015/02/05/top-10-easy-performance-optimisations-in- java/.- Author:
- Lukas Eder
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description void
clauseEnd(VisitContext context)
Called after leaving aClause
.void
clauseStart(VisitContext context)
Called before entering aClause
.void
visitEnd(VisitContext context)
Called after visiting aQueryPart
.void
visitStart(VisitContext context)
Called before visiting aQueryPart
.
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Method Detail
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clauseStart
void clauseStart(VisitContext context)
Called before entering aClause
.- See Also:
Context.start(Clause)
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clauseEnd
void clauseEnd(VisitContext context)
Called after leaving aClause
.- See Also:
Context.end(Clause)
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visitStart
void visitStart(VisitContext context)
Called before visiting aQueryPart
.Certain
VisitListener
implementations may chose to replace theQueryPart
contained in the argumentVisitContext
throughVisitContext.queryPart(QueryPart)
. This can be used for many use-cases, for example to add aCHECK OPTION
to an OracleINSERT
statement:
The above SQL transformation allows to prevent inserting new books for authors other than those with-- 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')
author_id IN (1, 2, 3)
- See Also:
Context.visit(QueryPart)
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visitEnd
void visitEnd(VisitContext context)
Called after visiting aQueryPart
.- See Also:
Context.visit(QueryPart)
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