org.hibernate.dialect.function
Class DerbyConcatFunction

java.lang.Object
  org.hibernate.dialect.function.DerbyConcatFunction

All Implemented Interfaces:

SQLFunction

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.

Author:

Steve Ebersole

Constructor Summary

DerbyConcatFunction()

Method Summary

Type	getReturnType(Type columnType, Mapping mapping) The return type of the function. Here we always return Hibernate.STRING.
boolean	hasArguments() Does this function have any arguments? Here we always return true
boolean	hasParenthesesIfNoArguments() If there are no arguments, are parens required? Here we always return true
String	render(List args, SessionFactoryImplementor factory) Render the function call as SQL fragment. Here's the meat..

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DerbyConcatFunction

public DerbyConcatFunction()

Method Detail

getReturnType

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

Parameters:

columnType - the type of the first argument

mapping - The mapping source.

Returns:

The type to be expected as a return.

Throws:

QueryException - Indicates an issue resolving the return type.

hasArguments

public boolean hasArguments()

Does this function have any arguments?

Here we always return true

Specified by:

hasArguments in interface SQLFunction

Returns:

True if the function expects to have parameters; false otherwise.

hasParenthesesIfNoArguments

public boolean hasParenthesesIfNoArguments()

If there are no arguments, are parens required?

Here we always return true

Specified by:

hasParenthesesIfNoArguments in interface SQLFunction

Returns:

True if a no-arg call of this function requires parentheses.

render

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

Parameters:

args - The function arguments

factory - The SessionFactory

Returns:

The rendered function call

Throws:

QueryException - Indicates a problem rendering the function call.