Oracle 11g Release 1 (11.1) PL/SQL_多维 Collection 类型和其异常

本文内容

• 多维 Collection
• Collection 异常

多维 Collection

虽然 collection 只有一维的，但可以模型一个多维的。创建一个 collection，其每个元素也是 collection 。例如，创建一个 varray 的 nested table，一个 varray 的 varray，一个 nested table 的 varray 等。

示例1：演示多维 varray

DECLARE
  TYPE t1 IS VARRAY(10) OF INTEGER;
  TYPE nt1 IS VARRAY(10) OF t1; -- multilevel varray type
  va t1 := t1(2,3,5);
  -- initialize multilevel varray
  nva nt1 := nt1(va, t1(55,6,73), t1(2,4), va);
  i INTEGER;
  va1 t1;
BEGIN
  -- multilevel access
  i := nva(2)(3); -- i will get value 73
  DBMS_OUTPUT.PUT_LINE('I = ' || i);
  -- add a new varray element to nva
  nva.EXTEND;
  -- replace inner varray elements
  nva(5) := t1(56, 32);
  nva(4) := t1(45,43,67,43345);
  -- replace an inner integer element
  nva(4)(4) := 1; -- replaces 43345 with 1
  -- add a new element to the 4th varray element
  -- and store integer 89 into it.
  nva(4).EXTEND;
  nva(4)(5) := 89;
END;
/

示例2：演示多维 nested table

DECLARE
  TYPE tb1 IS TABLE OF VARCHAR2(20);
  TYPE Ntb1 IS TABLE OF tb1; -- table of table elements
  TYPE Tv1 IS VARRAY(10) OF INTEGER;
  TYPE ntb2 IS TABLE OF tv1; -- table of varray elements
  vtb1 tb1 := tb1('one', 'three');
  vntb1 ntb1 := ntb1(vtb1);
  vntb2 ntb2 := ntb2(tv1(3,5), tv1(5,7,3));
  -- table of varray elements
BEGIN
  vntb1.EXTEND;
  vntb1(2) := vntb1(1);
  -- delete the first element in vntb1
  vntb1.DELETE(1);
  -- delete the first string
  -- from the second table in the nested table
  vntb1(2).DELETE(1);
END;
/

示例3：演示多维 associative array

DECLARE
  TYPE tb1 IS TABLE OF INTEGER INDEX BY PLS_INTEGER;
  -- the following is index-by table of index-by tables
  TYPE ntb1 IS TABLE OF tb1 INDEX BY PLS_INTEGER;
  TYPE va1 IS VARRAY(10) OF VARCHAR2(20);
  -- the following is index-by table of varray elements
  TYPE ntb2 IS TABLE OF va1 INDEX BY PLS_INTEGER;
  v1 va1 := va1('hello', 'world');
  v2 ntb1;
  v3 ntb2;
  v4 tb1;
  v5 tb1; -- empty table
BEGIN
  v4(1) := 34;
  v4(2) := 46456;
  v4(456) := 343;
  v2(23) := v4;
  v3(34) := va1(33, 456, 656, 343);
  -- assign an empty table to v2(35) and try again
  v2(35) := v5;
  v2(35)(2) := 78; -- it works now
END;
/

Collection 异常

示例 4：演示 Collection 异常

演示各种 PL/SQL 预定义的 collection  异常，备注的部分说明如何避免这些异常。

DECLARE
  TYPE WordList IS TABLE OF VARCHAR2(5);
  words WordList;
  err_msg VARCHAR2(100);
  PROCEDURE display_error IS
  BEGIN
    err_msg := SUBSTR(SQLERRM, 1, 100);
    DBMS_OUTPUT.PUT_LINE('Error message = ' || err_msg);
  END;
BEGIN
  BEGIN
    words(1) := 10; -- Raises COLLECTION_IS_NULL
--  A constructor has not been used yet.
--  Note: This exception applies to varrays and nested tables,
--  but not to associative arrays which do not need a constructor.
    EXCEPTION
      WHEN OTHERS THEN display_error;
  END;
--  After using a constructor, you can assign values to the elements.
    words := WordList('1st', '2nd', '3rd'); -- 3 elements created
--  Any expression that returns a VARCHAR2(5) is valid.
    words(3) := words(1) || '+2';
  BEGIN
    words(3) := 'longer than 5 characters'; -- Raises VALUE_ERROR
--  The assigned value is too long.
    EXCEPTION
      WHEN OTHERS THEN display_error;
  END;
  BEGIN
    words('B') := 'dunno'; -- Raises VALUE_ERROR
--  The subscript (B) of a nested table must be an integer.
--  Note: Also, NULL is not allowed as a subscript.
    EXCEPTION
      WHEN OTHERS THEN display_error;
  END;
  BEGIN
    words(0) := 'zero'; -- Raises SUBSCRIPT_OUTSIDE_LIMIT
--  Subscript 0 is outside the allowed subscript range.
    EXCEPTION
      WHEN OTHERS THEN display_error;
  END;
  BEGIN
    words(4) := 'maybe'; -- Raises SUBSCRIPT_BEYOND_COUNT
--  The subscript (4) exceeds the number of elements in the table.
--  To add new elements, invoke the EXTEND method first.
    EXCEPTION
      WHEN OTHERS THEN display_error;
  END;
  BEGIN
    words.DELETE(1);
    IF words(1) = 'First' THEN NULL; END IF;
      -- Raises NO_DATA_FOUND
--  The element with subcript (1) was deleted.
    EXCEPTION
      WHEN OTHERS THEN display_error;
  END;
END;
/

在子块处理产生的异常，执行就会继续。下面是一些异常：

Collection 异常	当……产生……
COLLECTION_IS_NULL	尝试操作一个自动为 null 的 collection
NO_DATA_FOUND	一个标值指定了一个被删除的元素，或一个 associative array 不存在的元素
SUBSCRIPT_BEYOND_COUNT	一个标值超过了一个 collection 元素的数量
SUBSCRIPT_OUTSIDE_LIMIT	一个标值超出了被允许的范围
VALUE_ERROR	一个标值为 null 或不能转换成键的类型。若键被定义为 PLS_INTEGER，或标值超出范围，则会产生该异常

在多数情况下，你可以传递一个不可靠的标值给方法，而不会产生异常。例如，当你传递一个 null 给 DELETE(n) 时，该方法什么都不会做。给已经删除的元素赋值，来替换这个已删除的元素，不会产生 NO_DATA_FOUND 异常。

示例 5：演示 DELETE(n) 如何处理不可靠的标值

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   nums NumList := NumList(10,20,30);  -- initialize table
BEGIN
   nums.DELETE(-1);  -- does not raise SUBSCRIPT_OUTSIDE_LIMIT
   nums.DELETE(3);   -- delete 3rd element
   DBMS_OUTPUT.PUT_LINE(nums.COUNT);  -- prints 2
   nums(3) := 30;    -- allowed; does not raise NO_DATA_FOUND
   DBMS_OUTPUT.PUT_LINE(nums.COUNT);  -- prints 3
END;
/

示例 6：演示包和本地 Collection 之间不兼容性

包的 collection 类型与本地 collection 类型不兼容。例如，若你调用包的存储过程，如下所示，第二个存储过程会调用失败，因为，包的和本地的 varray 类型不兼容，尽管它们具有相同的定义。

CREATE PACKAGE pkg AS
   TYPE NumList IS TABLE OF NUMBER;
   PROCEDURE print_numlist (nums NumList);
END pkg;
/
CREATE PACKAGE BODY pkg AS
  PROCEDURE print_numlist (nums NumList) IS
  BEGIN
    FOR i IN nums.FIRST..nums.LAST LOOP
      DBMS_OUTPUT.PUT_LINE(nums(i));
    END LOOP;
  END;
END pkg;
/

DECLARE
   TYPE NumList IS TABLE OF NUMBER;
   n1 pkg.NumList := pkg.NumList(2,4); -- type from the package.
   n2 NumList := NumList(6,8);         -- local type.
BEGIN
   pkg.print_numlist(n1); -- type from pkg is legal
-- The packaged procedure cannot accept
-- a value of the local type (n2)
-- pkg.print_numlist(n2);  -- Causes a compilation error.
END;
/