创建具有相同名称但不具有相同签名的别名 [英] create alias with the same name but not the same signature

问题描述

为了在Junit测试中使用H2数据库而不是调用Oracle，我被禁止在H2上创建别名以模拟某些Oracle兼容性:

In order to use H2 database in our Junit tests instead of calling Oracle, I am blocked on creating aliases on H2 to emulate some Oracle compatibility :

• 我首先声明了to_char的别名，以便将日期转换为char:可以正常工作

• I first declared an alias for to_char for date to char conversion : works fine

create alias TO_CHAR as $$ java.lang.String toChar(java.util.Date date, String format) throws Exception{ ... }$$;

然后我尝试为to_char声明一个别名，以将数字转换为char:现在h2不接受它: create alias TO_CHAR as $$ java.lang.String toChar(java.lang.Number value){ ... }$$;

Then I try to declare an alias for to_char for number to char conversion : now h2 doesn't accept it : create alias TO_CHAR as $$ java.lang.String toChar(java.lang.Number value){ ... }$$;

它被拒绝，并显示以下错误消息:

It is rejected with the following error message :

org.h2.jdbc.JdbcSQLException:函数别名"TO_CHAR"已经存在； SQL语句: 创建别名TO_CHAR为$$

org.h2.jdbc.JdbcSQLException: Function alias "TO_CHAR" already exists; SQL statement: create alias TO_CHAR as $$

java.lang.String toChar(java.lang.Number值){ 返回java.lang.String .valueOf(value); } $$

java.lang.String toChar(java.lang.Number value){ return java.lang.String .valueOf(value); }$$

我还试图在1个块中声明2个函数，例如:

I also tried to declare the 2 functions in 1 block, like :

将别名TO_CHAR创建为$$

create alias TO_CHAR as $$

java.lang.String toChar(int value){ ... }

java.lang.String toChar(int value){ ... }

java.lang.String toChar(java.util.Date date，String format)抛出 例外{ ... } $$;

java.lang.String toChar(java.util.Date date, String format) throws Exception{ ... } $$;

在这种情况下，没有错误，但仅考虑了声明的firest方法.

In this case, there are no errors, but only the firest method declared is taken in account.

那么，有什么办法可以声明两个具有相同名称但不具有相同签名的别名?

So, is there any way to declare 2 aliases having the same name but not the same signature ?

推荐答案

对于 TO_CHAR， H2现在支持它，因为版本1.3.175(2013-01-18).

As for TO_CHAR, H2 support it now, since version 1.3.175 (2013-01-18).

H2确实支持函数重载.但是，存在局限性，因为不支持将此类功能声明为源代码.

H2 does support function overloading. However, there is a limitation, because declaring such functions as source code is not supported.

您需要按以下方式声明方法:

You would need to declare the method as follows:

CREATE ALIAS YOUR_METHOD FOR "acme.Function.yourMethod";

此限制记录在用户定义的函数中，如下所示:

This limitation is documented under User Defined Functions as follows:

如果已编译该类并将其包含在类路径中，则可以将多个方法绑定到SQL函数.每个Java方法必须具有不同数量的参数.将函数声明为源代码时，不支持方法重载.

Multiple methods may be bound to a SQL function if the class is already compiled and included in the classpath. Each Java method must have a different number of arguments. Method overloading is not supported when declaring functions as source code.

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