Table of Contents
This module enables usage of full featured Apache Velocity templates in org.apache.cayenne.query.SQLTemplate
queries.
<dependency> <groupId>org.apache.cayenne</groupId> <artifactId>cayenne-velocity</artifactId> <version>4.1.M1</version> </dependency>
This module doesn't require any additional setup.
In addition of directives mentioned in this chapter, this module enables #chain and #chunk
directives.
#chain and #chunk directives are used for
conditional inclusion of SQL code. They are used together with
#chain wrapping multiple #chunks. A chunk
evaluates its parameter expression and if it is NULL suppresses rendering of the
enclosed SQL block. A chain renders its prefix and its chunks joined by the
operator. If all the chunks are suppressed, the chain itself is suppressed. This
allows to work with otherwise hard to script SQL semantics. E.g. a WHERE clause
can contain multiple conditions joined with AND or OR. Application code would
like to exclude a condition if its right-hand parameter is not present (similar
to Expression pruning discussed above). If all conditions are excluded, the
entire WHERE clause should be excluded. chain/chunk allows to do that.
Semantics:
#chain(operator) ... #end #chain(operator prefix) ... #end #chunk() ... #end #chunk(param) ... #end
Full example:
#chain('OR' 'WHERE') #chunk($name) NAME LIKE #bind($name) #end #chunk($id) ARTIST_ID > #bind($id) #end #end"