如何调用 Oracle PL/SQL 对象超级方法

2021-12-24 00:00:00 oop oracle oracle10g plsql

我想调用一个重写的 PL/SQL 方法.举个例子:

I'd like to call an overridden PL/SQL method. Here's an example:

-- super class
create or replace type test as object
(
  n number,
  member procedure proc(SELF in out nocopy test, s varchar2)
)
alter type test not final
/

create or replace type body test is
  member procedure proc(SELF in out nocopy test, s varchar2) is
  begin
    dbms_output.put_line('test1: n='||nvl(self.n, 'null')||' s='||s);
    self.n := to_number(s);
  end;
end;
/

-- derived class
create or replace type test2 under test
(
  overriding member procedure proc(SELF in out nocopy test2, s varchar2)
)
/

现在我想调用 proc 方法的继承版本.当我尝试执行像 treat(self as test).proc(s); 这样的显式转换时，它不会编译，因为 PLS-00363: expression 'SYS_TREAT' cannot be used as分配目标

Now I want to invoke the inherited version of the proc method. When I try to do an explicit cast like treat(self as test).proc(s); it won't compile because of PLS-00363: expression 'SYS_TREAT' cannot be used as an assignment target

类型主体在我使用局部变量时编译:

The type body compiles when I use a local variable:

create or replace type body test2 is
  overriding member procedure proc(SELF in out nocopy test2, s varchar2) is 
    O test;
  begin
    O := treat(self as test);
    O.proc(s);
  end;
end;
/

但是当我像这样运行我的例子时

But when I run my example like this

declare
  obj test2;
begin
  obj := test2(0);
  obj.proc('1');
end;

...它抛出ORA-21780:超出对象持续时间的最大数量.

有什么方法可以调用 test::proc(无需序列化/反序列化)?

Is there any way to call test::proc (without serializing/deserializing)?

而且...在proc被调用后，如何在obj中反映任何改变的属性(即n)?

And... after proc has been called, how can any changed attributes (namely n) be reflected in obj ?

更新(谢谢，tbone):

Update (Thanks, tbone):

我使用模板方法(之前"和之后")更改了我的方法的组织.每当我需要扩展方法时，我都会添加它们.

I changed the organization of my methods using template methods ('before' and 'after'). I add them whenever I need to extend a method.

create or replace type test as object
(
  n number,
  member procedure proc      (SELF in out nocopy test, s varchar2),
  member procedure afterProc (SELF in out nocopy test, s varchar2)
  member procedure beforeProc(SELF in out nocopy test, s varchar2),
)
not final
/

create or replace type body test is
  member procedure proc(SELF in out nocopy test, s varchar2) is
  begin
    beforeProc(s);
    dbms_output.put_line('test1: n='||nvl(n, 'null')||' s='||s);
    n := to_number(s);
    afterProc(s);
  end;
  member procedure afterProc (SELF in out nocopy test, s varchar2) is begin null; end;
  member procedure beforeProc(SELF in out nocopy test, s varchar2) is begin null; end;
end;
/

推荐答案

要访问超级方法，请尝试通用调用或通用表达式.例如，使用个人超类型和学生子类型:

To access the super methods, try either general invocation or generalized expression. For example, using a person supertype and student subtype:

CREATE OR REPLACE TYPE person_typ AS OBJECT (
    idno number,
    name varchar2(30),
    phone varchar2(20),
    MAP MEMBER FUNCTION get_idno RETURN NUMBER,
    MEMBER FUNCTION show RETURN VARCHAR2)
NOT FINAL;

CREATE OR REPLACE TYPE BODY person_typ AS
  MAP MEMBER FUNCTION get_idno RETURN NUMBER IS
  BEGIN
    RETURN idno;
  END;
  MEMBER FUNCTION show RETURN VARCHAR2 IS
  BEGIN
    -- function that can be overriden by subtypes MEMBER FUNCTION show RETURN VARCHAR2 IS BEGIN
    RETURN 'Id: ' || TO_CHAR(idno) || ', Name: ' || name;
  END;
END;

CREATE TYPE student_typ UNDER person_typ (
    dept_id NUMBER,
    major VARCHAR2(30),
    OVERRIDING MEMBER FUNCTION show RETURN VARCHAR2)
NOT FINAL;

CREATE TYPE BODY student_typ AS
  OVERRIDING MEMBER FUNCTION show RETURN VARCHAR2 IS
  BEGIN
    RETURN (self AS person_typ).show || ' -- Major: ' || major ;
  END;
END;

-- Using Generalized Invocation
DECLARE
myvar student_typ := student_typ(100, 'Sam', '6505556666', 100, 'Math');
name VARCHAR2(100); 
BEGIN
name := (myvar AS person_typ).show; --Generalized invocation 
END;

-- Using Generalized Expression
DECLARE
myvar2 student_typ := student_typ(101, 'Sam', '6505556666', 100, 'Math');
name2 VARCHAR2(100); 
BEGIN
name2 := person_typ.show((myvar2 AS person_typ)); -- Generalized expression 
END;

如果您使用的是 10g，则需要对函数进行一些不同的组织，但与调用 super 方法的子函数具有相同的功能:

If you are on 10g, you'll need to organize the functions a bit different, but same functionality from the child to call the super method:

CREATE TYPE BODY person_typ AS 
  MAP MEMBER FUNCTION get_idno RETURN NUMBER IS 
  BEGIN
    RETURN idno; 
  END;
  -- static function that can be called by subtypes 
  STATIC FUNCTION show_super (person_obj in person_typ) RETURN VARCHAR2 IS
  BEGIN 
    RETURN 'Id: ' || TO_CHAR(person_obj.idno) || ', Name: ' || person_obj.name;
  END;
  -- function that can be overriden by subtypes 
  MEMBER FUNCTION show RETURN VARCHAR2 IS 
  BEGIN
    RETURN person_typ.show_super ( SELF ); 
  END;
END;

CREATE TYPE student_typ UNDER person_typ ( 
  dept_id NUMBER,
  major VARCHAR2(30), 
  OVERRIDING MEMBER FUNCTION show RETURN VARCHAR2) 
  NOT FINAL;

CREATE TYPE BODY student_typ AS 
  OVERRIDING MEMBER FUNCTION show RETURN VARCHAR2 IS 
  BEGIN
    RETURN person_typ.show_super ( SELF ) || ' -- Major: ' || major ;
  END;
END;

现在您可以从 student 中为 person 方法调用 show_super()，或者为 student 方法调用 show().

Now you'd call show_super() from student for the person method, or just show() for the student method.

来自文档，希望有所帮助.

From the docs, hope that helps.

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