本文内容多维CollectionCollection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 本文内容 多维 Collection Collection 异常 多维 Collection 虽
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; /