Class DerbyConcatFunction

  extended by org.hibernate.dialect.function.DerbyConcatFunction
All Implemented Interfaces:

public class DerbyConcatFunction
extends 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.

Steve Ebersole

Constructor Summary
Method Summary
 Type getReturnType(Type columnType, Mapping mapping)
          The return type of the function.
 boolean hasArguments()
          Does this function have any arguments?
 boolean hasParenthesesIfNoArguments()
          If there are no arguments, are parens required?
 String render(List args, SessionFactoryImplementor factory)
          Render the function call as SQL fragment.
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public DerbyConcatFunction()
Method Detail


public Type getReturnType(Type columnType,
                          Mapping mapping)
                   throws QueryException
The return type of the function. May be either a concrete type which is preset, or variable depending upon the type of the first function argument.

Here we always return Hibernate.STRING.

Specified by:
getReturnType in interface SQLFunction
columnType - the type of the first argument
mapping - The mapping source.
The type to be expected as a return.
QueryException - Indicates an issue resolving the return type.


public boolean hasArguments()
Does this function have any arguments?

Here we always return true

Specified by:
hasArguments in interface SQLFunction
True if the function expects to have parameters; false otherwise.


public boolean hasParenthesesIfNoArguments()
If there are no arguments, are parens required?

Here we always return true

Specified by:
hasParenthesesIfNoArguments in interface SQLFunction
True if a no-arg call of this function requires parentheses.


public String render(List args,
                     SessionFactoryImplementor factory)
              throws QueryException
Render the function call as SQL fragment.

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
args - The function arguments
factory - The SessionFactory
The rendered function call
QueryException - Indicates a problem rendering the function call.

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