Oracle:无法更改此触发器类的New值

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今天在平时ERP的维护和管理中遇到一个问题,当一个值发生变化时,指定内容的值需要发生变化,

1、若该值由0变成1时,系统不做任何改变;

2、若该值由1变成0时,系统根据实际需求,删除或清空该类的小项内容。

因此,结合该需求,笔者结合触发器的原理和用途,选择运用触发器来解决这一需求。

一开始,笔者未了解清楚:new的使用范畴,因此在书写触发器时将其写在after之后执行,编译时报出了“无法更改此触发器类的New值”异常,于是开始寻找原因。之后才知道After时:new值只有读的权限,没有写的权限,而Before时:new有读写权限,因此将After改为Before,编译成功!

SQL如下:

修改前:

create or replace trigger tri_app1_mstr_upd after update on app1_mstr
for each row
begin
  if updating then
    if :new.app_hardware = 0 and :old.app_hardware = 1 then
      :new.app_1_dept      := ‘‘;
      :new.app_1_mgr1      := ‘‘;
      :new.app_1_summary   := ‘‘;
      :new.app_1_engineer1 := ‘‘;
      :new.app_1_engineer2 := ‘‘;
      :new.app_1_engineer3 := ‘‘;
      
      delete from appd6_det where appd6_flow = :old.app_flow;
    end if;        
  end if; 
end tri_app1_mstr_upd;
View Code

修改后:

create or replace trigger tri_app1_mstr_upd before update on app1_mstr
for each row
begin
  if updating then
    if :new.app_hardware = 0 and :old.app_hardware = 1 then
      :new.app_1_dept      := ‘‘;
      :new.app_1_mgr1      := ‘‘;
      :new.app_1_summary   := ‘‘;
      :new.app_1_engineer1 := ‘‘;
      :new.app_1_engineer2 := ‘‘;
      :new.app_1_engineer3 := ‘‘;
      
      delete from appd6_det where appd6_flow = :old.app_flow;
    end if;
    
    if :new.app_structure = 0 and :old.app_structure = 1 then
      :new.app_2_dept       :=‘‘;
      :new.app_2_mgr1       :=‘‘;
      :new.app_2_summary    :=‘‘;
      :new.app_2_engineer1  :=‘‘;
      :new.app_2_engineer2  :=‘‘;
      :new.app_2_engineer3  :=‘‘;
      
      delete from appd7_det where appd7_flow = :old.app_flow;
    end if;
    
    if :new.app_software = 0 and :old.app_software = :old.app_flow then
      :new.app_3_dept       :=‘‘;
      :new.app_3_mgr1       :=‘‘;
      :new.app_3_summary    :=‘‘;
      :new.app_3_engineer1  :=‘‘;
      :new.app_3_engineer2  :=‘‘;
      :new.app_3_engineer3  :=‘‘;
      
      delete from appd8_det where appd8_flow = :old.app_flow;
    end if;
    
    if :new.app_other = 0 and :old.app_other = 1 then
      :new.app_4_dept       :=‘‘;
      :new.app_4_mgr1       :=‘‘;
      :new.app_4_summary    :=‘‘;
      :new.app_4_engineer1  :=‘‘;
      :new.app_4_engineer2  :=‘‘;
      :new.app_4_engineer3  :=‘‘;
      
      delete from appd9_det where appd9_flow = :old.app_flow;
    end if;
    
    if :new.app_module = 0 and :old.app_module = 1 then
      :new.app_5_dept       :=‘‘;
      :new.app_5_mgr1       :=‘‘;
      :new.app_5_summary    :=‘‘;
      :new.app_5_engineer1  :=‘‘;
      :new.app_5_engineer2  :=‘‘;
      :new.app_5_engineer3  :=‘‘;
      
      delete from appd12_det where appd12_flow = :old.app_flow;
    end if;    
  end if; 
end tri_app1_mstr_upd;
View Code