如何使用 Oracle 触发器（和域表）代替检查约束来强制列范围

Question

此触发器 (Oracle 12c) 旨在停止在列（价格）大于变量的表（MainTable aka Room）中插入和更新行。变量的值取决于另一列（类型）。共有三种“类型”（S、D、K），“类型”允许的最高价格分别为 100、150 和 200。触发器通过引用具有两列和三行的域表（DomainTable aka RoomType）来工作，如下所示 [roomTypeCode(S, D, K), maxPrice(100, 150, 200)] 并确保：

...IF new MainTable.type = 'S', THEN new MainTable.price

...IF new MainTable.type = 'D', THEN new MainTable.price

...IF new MainTable.type = 'K', THEN new MainTable.price

这是我失败的尝试。

CREATE TRIGGER Room_Type_Price_Range
  BEFORE INSERT OR UPDATE ON room
  REFERENCING NEW AS newRec
  FOR EACH ROW
  DECLARE
    SELECT maxPrice INTO singleRmMax FROM RoomType WHERE RoomTypeCode = 'S';
    SELECT maxPrice INTO doubleRmMax FROM RoomType WHERE RoomTypeCode = 'D';
    SELECT maxPrice INTO kingRmMax FROM RoomType WHERE RoomTypeCode = 'K';
  BEGIN
     IF (   (:newRec.type = 'S' AND :newRec.price > singleRmMax)
        OR  (:newRec.type = 'D' AND :newRec.price > doubleRmMax)
        OR  (:newRec.type = 'K' AND :newRec.price > kingRmMax)
        )
        RAISE_APPLICATION_ERROR(-20001, 'Price constraint violated.  
          \nCannot Insert/Update in this table.');
  END;

我的错误信息：

04098. 00000 -  "trigger '%s.%s' is invalid and failed re-validation"
*Cause:    A trigger was attempted to be retrieved for execution and was
           found to be invalid.  This also means that compilation/authorization
           failed for the trigger.
*Action:   Options are to resolve the compilation/authorization errors,
           disable the trigger, or drop the trigger.

感谢您的帮助！

Answer 1

当您创建触发器时，您会看到诸如“编译时带有警告”或“错误：检查编译器日志”之类的消息。此时您可以通过show errors 来查看编译失败的原因，或者查看 SQL Developer 的编译器日志窗口。

当您插入或更新the invalid trigger is automatically recompiled，但由于它仍然无效，您会收到 ORA-04098 错误。您仍然可以通过查询user_errors 视图来查看问题所在：

select line, position, text
from user_errors
where type = 'TRIGGER'
and name = 'ROOM_TYPE_PRICE_RANGE'
order by sequence;

您的代码给出了三个错误；只显示每一行的第一行：

LINE POSITION TEXT
---- -------- -------------------------------------------------------------------------------------------------
   2        5 PLS-00103: Encountered the symbol "SELECT" when expecting one of the following:
  10        9 PLS-00103: Encountered the symbol "RAISE_APPLICATION_ERROR" when expecting one of the following:
  11       50 PLS-00103: Encountered the symbol ";" when expecting one of the following:

正如 David Faber 在评论中指出的那样，第一个错误是因为您的声明部分中有一个 select 语句；也许此时查看the structure of a subprogram 会很有用。

第二个错误是因为您的IF 没有THEN 关键字，第三个错误是因为您也没有END IF。只需清理您必须正确声明和填充变量的内容，您就会得到类似：

DECLARE
  singleRmMax RoomType.MaxPrice%TYPE;
  doubleRmMax RoomType.MaxPrice%TYPE;
  kingRmMax RoomType.MaxPrice%TYPE;
BEGIN
  SELECT maxPrice INTO singleRmMax FROM RoomType WHERE RoomTypeCode = 'S';
  SELECT maxPrice INTO doubleRmMax FROM RoomType WHERE RoomTypeCode = 'D';
  SELECT maxPrice INTO kingRmMax FROM RoomType WHERE RoomTypeCode = 'K';

  IF (   (:newRec.type = 'S' AND :newRec.price > singleRmMax)
    OR  (:newRec.type = 'D' AND :newRec.price > doubleRmMax)
    OR  (:newRec.type = 'K' AND :newRec.price > kingRmMax)
    ) THEN
    RAISE_APPLICATION_ERROR(-20001, 'Price constraint violated.  
      \nCannot Insert/Update in this table.');
  END IF;
END;

不过，您实际上并不需要三个变量，您只需查询您感兴趣的房间类型即可：

DECLARE
  roomTypeMax RoomType.MaxPrice%TYPE;
BEGIN
  SELECT maxPrice INTO roomTypeMax
  FROM RoomType
  WHERE RoomTypeCode = :newRec.type;

  IF :newRec.price > roomTypeMax THEN
    RAISE_APPLICATION_ERROR(-20001,
      'Price constraint violated. Cannot Insert/Update in this table.');
  END IF;
END;

我还从错误消息中删除了\n，因为无论插入什么都可能将其视为两个文字字符而不是换行符。

您可能还想考虑捕获no_data_found 并提出您自己的异常，因为这表明新房间类型不存在，因此在任何价格上都无效。