在 pl/sql 中处理异常

Question

我正在使用 Oracle Forms 10g 构建一个 GUI，通过填写表单将用户添加到数据库。以下是我在Add User 按钮上的when-button-pressed 触发器上使用的代码：

代码：

declare
    firstname VARCHAR(15);
    lastname VARCHAR(15);
    usernameee VARCHAR(15);
    emailll VARCHAR(15);
    pass1 VARCHAR(15);
    pass2 VARCHAR(15);
    v varchar2(200);
begin
    firstname := :HOMEADMIN1.TXTFIRSTNAME;
    lastname := :HOMEADMIN1.TXTLASTNAME;
    usernameee := :HOMEADMIN1.TXTUSERNAME;
    emailll := :HOMEADMIN1.TXTEMAIL;
    pass1 := :HOMEADMIN1.TXTPASSWORD;
    pass2 := :HOMEADMIN1.TXTPASSWORD2;

    if firstname is null or lastname is null or usernameee is null or 
        emailll is null or pass1 is null or pass2 is null then
        message('Please fill all fields');
    else
        select Firstname into v from Person where Username = usernameee;
        if sql%found then
            message('This username is already taken');
        else
            select Firstname into v from Person where Email = emailll;
            if sql%found then
                message('This email is already taken');
            else
                insert into Person values (PersonSeq.nextval,firstname,lastname,usernameee,pass1,emailll,0,1);
                commit;
            end if;
        end if;
    end if;
end;

此代码检查是否所有输入 textboxes 都已填充（有效），然后它必须检查输入的 username 和 email 是否已被使用。代码编译得很好，但是当我输入任何email 或username 时，我得到一个error 01403，这表明我必须处理NO_DATA_FOUND exception。 你能告诉我如何在我的代码中做到这一点吗？我被卡住了，因为我有 2 个条件（查询）需要处理，但我不知道如何处理。任何帮助将不胜感激。

Answer 1

您感兴趣的行是获取“名字”的 SELECT 语句（具有不同的条件 - 一次通过用户名，然后通过电子邮件）。

一种方法是使用聚合函数，例如MAX：

select max(Firstname) into v from Person where Username = usernameee;

这样做不会引发 NO-DATA-FOUND。

不过，这只是一个不错的解决方法。正确的方法是正确处理异常。为此，您需要将这些 SELECT 语句包含在它们自己的 BEGIN-EXCEPTION-END 块中，例如：

else
  -- First, check whether USERNAME is taken:
  begin
    select firstname into v from person where username = usernameee;

    -- You don't need IF SQL%FOUND because - if SELECT returned a value, you'll
    -- get here anyway
    message('This username is already taken');
    raise form_trigger_failure;   --> this is Forms, isn't it?

    exception
    -- SELECT returned nothing and raised an exception
    when no_data_found then 
      -- do nothing; proceed to EMAIL validation
      null;
  end;

  -- Username is available (because previous RAISE didn't fire
  begin
    select firstname into v from person where email = emailll;

    message('This email is already taken');
    raise form_trigger_failure;

  exception
    when no_data_found then
      null; 
  end;

  insert into person values (...);
  commit;
end if;

Answer 2

作为@Littlefoot 提供的解决方案的替代方案，您可以将每个验证拆分为自己的单独程序。主过程然后几乎没有逻辑。验证需求并插入或仅处理需求异常。所以：

declare
    -- internal exceptions 
    not_all_fields_entered  exception; 
    user_name_already_taken exception; 
    email_already_taken     exception; 

    -- variables
    firstname VARCHAR(15);
    lastname VARCHAR(15);
    usernameee VARCHAR(15);
    emailll VARCHAR(15);
    pass1 VARCHAR(15);
    pass2 VARCHAR(15);

    -- validaion routines
    procedure validate_fields_entered
    is
    begin 
        if firstname is null or lastname is null or usernameee is null  
        or emailll is null or pass1 is null or pass2 is null  
        then
            raise not_all_fields_entered;
        end if;
    end validate_fields_entered; 

    procedure validate_user_name_not_taken
    is 
        user_name_count integer; 
    begin 
         select count(*) 
           into user_name_count
           from Person 
          where Username = usernameee
            and rownum < 2;
        if user_name_count = 1  
        then 
           raise user_name_already_taken;
        end if;
    end validate_user_name_not_taken; 

    procedure validate_email_not_taken
    is 
        email_use_count integer; 
    begin 
         select count(*) 
           into email_use_count
           from Person 
          where Email = emailll
            and rownum < 2;
        if email_use_count = 1  
        then 
           raise email_already_taken;
        end if;
    end validate_user_name_not_taken;     

begin
    firstname := :HOMEADMIN1.TXTFIRSTNAME;
    lastname := :HOMEADMIN1.TXTLASTNAME;
    usernameee := :HOMEADMIN1.TXTUSERNAME;
    emailll := :HOMEADMIN1.TXTEMAIL;
    pass1 := :HOMEADMIN1.TXTPASSWORD;
    pass2 := :HOMEADMIN1.TXTPASSWORD2;

    -- do validations
    validate_fields_entered;
    validate_user_name_not_taken;
    validate_email_not_taken;

    -- all good insert the row 
    insert into Person values (PersonSeq.nextval,firstname,lastname,usernameee,pass1,emailll,0,1);

exception 
    when not_all_fields_entered  then 
         message('Please fill all fields');
    when user_name_already_taken then  
         message('This username is already taken');
    when email_already_taken then  
          message('This email is already taken');
    when others then 
         log_error (....) ; 
         raise ;
end;

我知道这里没有指定，但请考虑维护。如果需求发生变化，需要什么： 1.如果没有采取验证电子邮件的格式是正确的。 2. 验证密码是否相同且满足复杂性规则。