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

Constructors

Constructor and Description
DerbyConcatFunction()

Method Summary

Modifier and Type	Method and Description
Type	getReturnType(Type argumentType, Mapping mapping) The return type of the function.
boolean	hasArguments() Does this function have any arguments?
boolean	hasParenthesesIfNoArguments() If there are no arguments, are parentheses required?
String	render(Type argumentType, 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

DerbyConcatFunction

public DerbyConcatFunction()

Method Detail

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 parentheses required?

Here we always return true

Specified by:

hasParenthesesIfNoArguments in interface SQLFunction

Returns:

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

getReturnType

public Type getReturnType(Type argumentType,
                          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.

Note, the 'firstArgumentType' parameter should match the one passed into SQLFunction.render(org.hibernate.type.Type, java.util.List, org.hibernate.engine.spi.SessionFactoryImplementor)

Here we always return StandardBasicTypes.STRING.

Specified by:

getReturnType in interface SQLFunction

Parameters:

argumentType - 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.

render

public String render(Type argumentType,
                     List args,
                     SessionFactoryImplementor factory)
              throws QueryException

Render the function call as SQL fragment.

Note, the 'firstArgumentType' parameter should match the one passed into SQLFunction.getReturnType(org.hibernate.type.Type, org.hibernate.engine.spi.Mapping)

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 concatenation 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:

argumentType - The type of the first argument

args - The function arguments

factory - The SessionFactory

Returns:

The rendered function call

Throws:

QueryException - Indicates a problem rendering the function call.