org.hibernate.dialect.function

Class DerbyConcatFunction

Implemented Interfaces:
SQLFunction

public class DerbyConcatFunction
extends java.lang.Object
implements SQLFunction

A specialized concat() function definition in which:
  1. we translate to use the concat operator ('||')
  2. wrap dynamic parameters in CASTs to VARCHAR

This last spec is to deal with a limitation on DB2 and variants (e.g. Derby) where dynamic parameters cannot be used in concatenation unless they are being concatenated with at least one non-dynamic operand. And even then, the rules are so convoluted as to what is allowed and when the CAST is needed and when it is not that we just go ahead and do the CASTing.

Author:
Steve Ebersole

Method Summary

Type
getReturnType(Type columnType, Mapping mapping)
Here we always return Hibernate.STRING.
boolean
hasArguments()
Here we always return true
boolean
hasParenthesesIfNoArguments()
Here we always return true
String
render(List args, SessionFactoryImplementor factory)
Here's the meat..

Method Details

getReturnType

public Type getReturnType(Type columnType,
                          Mapping mapping)
            throws QueryException
Here we always return Hibernate.STRING.
Specified by:
getReturnType in interface SQLFunction

hasArguments

public boolean hasArguments()
Here we always return true
Specified by:
hasArguments in interface SQLFunction

hasParenthesesIfNoArguments

public boolean hasParenthesesIfNoArguments()
Here we always return true
Specified by:
hasParenthesesIfNoArguments in interface SQLFunction

render

public String render(List args,
                     SessionFactoryImplementor factory)
            throws QueryException
Here's the meat.. The whole reason we have a separate impl for this for Derby is to re-define this method. The logic here says that if not all the incoming args are dynamic parameters (i.e. ?) then we simply use the Derby concat operator (||) on the unchanged arg elements. However, if all the args are dynamic parameters, then we need to wrap the individual arg elements in cast function calls, use the concantenation operator on the cast returns, and then wrap that whole thing in a call to the Derby varchar function.
Specified by:
render in interface SQLFunction