public class

DerbyConcatFunction

extends Object
implements SQLFunction
java.lang.Object
   ↳ org.hibernate.dialect.function.DerbyConcatFunction

Class Overview

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.

Summary

Public Constructors
DerbyConcatFunction()
Public Methods
Type getReturnType(Type argumentType, Mapping mapping)
The return type of the function.

Here we always return STRING.

boolean hasArguments()
Does this function have any arguments?

Here we always return true

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

Here we always return true

String render(Type argumentType, List args, SessionFactoryImplementor factory)
Render the function call as SQL fragment.

Here's the meat..

[Expand]
Inherited Methods
From class java.lang.Object
From interface org.hibernate.dialect.function.SQLFunction

Public Constructors

public DerbyConcatFunction ()

Public Methods

public Type getReturnType (Type argumentType, Mapping mapping)

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 render(Type, List, SessionFactoryImplementor)

Here we always return STRING.

Parameters
argumentType The type of the first argument
mapping The mapping source.
Returns
  • The type to be expected as a return.
Throws
QueryException

public boolean hasArguments ()

Does this function have any arguments?

Here we always return true

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

public boolean hasParenthesesIfNoArguments ()

If there are no arguments, are parentheses required?

Here we always return true

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

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

Render the function call as SQL fragment.

Note, the 'firstArgumentType' parameter should match the one passed into getReturnType(Type, 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.

Parameters
argumentType The type of the first argument
args The function arguments
factory The SessionFactory
Returns
  • The rendered function call
Throws
QueryException