程序包 org.hibernate.dialect.function

类 DerbyConcatFunction

java.lang.Object

org.hibernate.dialect.function.DerbyConcatFunction

所有已实现的接口:

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.

作者:

Steve Ebersole

构造器概要

构造器

构造器	说明
DerbyConcatFunction()

方法概要

修饰符和类型	方法	说明
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.

从类继承的方法 java.lang.Object

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

构造器详细资料

DerbyConcatFunction

public DerbyConcatFunction()

方法详细资料

hasArguments

public boolean hasArguments()

Does this function have any arguments?

Here we always return true

指定者:

hasArguments 在接口中 SQLFunction

返回:

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

指定者:

hasParenthesesIfNoArguments 在接口中 SQLFunction

返回:

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.

指定者:

getReturnType 在接口中 SQLFunction

参数:

argumentType - The type of the first argument

mapping - The mapping source.

返回:

The type to be expected as a return.

抛出:

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.

指定者:

render 在接口中 SQLFunction

参数:

argumentType - The type of the first argument

args - The function arguments

factory - The SessionFactory

返回:

The rendered function call

抛出:

QueryException - Indicates a problem rendering the function call.