如果参数名称太长，则回滚事务

Question

我正在使用您创建新的.NET MVC应用程序时开箱即用的SimpleMembershipProvider，并且我希望允许管理员用户添加角色。出于学习目的，（我不知道这是否是正确的方法）我想将RoleName列的描述长度限制为15个字符，所以我写了这个事务：

create proc spInsertRole
(
    @roleName varchar(50)
    --really shouldn't be 50, but that's
    --how I originally wrote my code
)
as
begin
    set nocount on
begin try
    begin tran
    insert into dbo.webpages_Roles(RoleName)
    values (@roleName)
    commit transaction
end try
begin catch
    select ERROR_MESSAGE() as ErrorMessage
    if len(@roleName) > 15
    rollback transaction
end catch
end

表上没有对RoleName长度的检查约束。这个proc会编译，但它也会让我添加一个大于15个字符的RoleName。我错过了什么，最好的方法是什么？

Answer 1

在运行insert语句之前，应检查的长度。通过将长度检查放入catch块，您告诉程序只检查长度并在有其他错误情况时回滚。

（我的T-SQL生锈了，我没有要测试的数据库所以请在接受之前进行验证。另外，鉴于这些更改，您可能不再需要交易。）

create proc spInsertRole
(
    @roleName varchar(50)
    --really shouldn't be 50, but that's
    --how I originally wrote my code
)
as
begin
    set nocount on
    begin try
        begin tran
        -- length check moved here.  Raise error when > 15.
        -- Severity (argument 2) needs to be higher than 10
        -- to stop execution and trigger the catch block.
        -- State (argument 3) is an arbitrary value between 0 and 255.
        if len(@roleName) > 15 
            raiserror('Role name is too long.', 11, 5)
        insert into dbo.webpages_Roles(RoleName)
        values (@roleName)
        commit transaction
    end try
    begin catch
        select ERROR_MESSAGE() as ErrorMessage
        -- length check was here. program will always roll back now.
        rollback transaction
    end catch
end

有关其工作原理的详情，请参阅RAISERROR。