Class DerbyConcatFunction

  • All Implemented Interfaces:

    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.

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

        public java.lang.String render​(Type argumentType,
                                       java.util.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
        argumentType - The type of the first argument
        args - The function arguments
        factory - The SessionFactory
        The rendered function call
        QueryException - Indicates a problem rendering the function call.