Oracle:为对象类型列指定默认值

问题描述

我有一个带有无参数构造函数的对象类型，但是当我将其指定为该类型列的默认值时，会收到ORA-00904:无效的标识符错误.

I have an object type with no-args constructor, but when I specify it as default value for a column of that type, I get ORA-00904: invalid identifier error.

示例:

CREATE OR REPLACE TYPE test_t AS OBJECT
(
  val      NUMBER(10),
  CONSTRUCTOR FUNCTION test_t return self as result
)

CREATE OR REPLACE TYPE BODY test_t AS
  CONSTRUCTOR FUNCTION test_t RETURN SELF AS RESULT IS
  BEGIN
    val := 1;
    RETURN;
  END;
END;

CREATE TABLE test_table (
    test_attr test_t DEFAULT new test_t()
)

Error: ORA-00904: "INKA"."TEST_T"."TEST_T": invalid identifier

如果我将DEFAULT替换为例如test_t(1)，它可以工作，但是这种方式打破了OO封装范例，我希望所有相同类型的字段都具有相同的默认默认值"(希望您知道我的意思是:-)

If I replace DEFAULT with e.g. test_t(1), it works, but that sort of breaks the OO encapsulation paradigm, I want all fields of same type to have same default "default values" (hope you know what I mean :-)

我是否在这里遗漏了一些东西，或者这是正常现象，并且无法使用像这样的非默认构造函数吗?

Am I missing something here, or is this normal and it is not possible to use non-default constructors like this?

推荐答案

看起来不可能这样.

一种解决方法是使用触发器:

One workaround would be to use a trigger:

CREATE OR REPLACE TRIGGER test_trigger
  BEFORE INSERT OR UPDATE
ON test_table
  FOR EACH ROW
WHEN ( new.test_attr IS NULL )
BEGIN
  :new.test_attr := NEW test_t();
END test_trigger;
/

---

顺便说一句，它不会完全忽略非默认构造函数，而会覆盖默认构造函数

---

It does not completely ignore non-default constructors by the way, overriding the default constructor

CONSTRUCTOR FUNCTION test_t(in_val NUMBER)
RETURN SELF AS RESULT

尝试使用DEFAULT NEW test_t(1)定义表时，

导致异常:

leads to an exception when trying to define the table with DEFAULT NEW test_t(1):

这篇关于Oracle:为对象类型列指定默认值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！