一次编写，随处运行
| d auth with a table called users. There is one index on the field user_id. There is one row in the table as well. We also have a sequence called users_user_id which will be initialized at 1. The next value in the sequence will therefore be 2. Finally, a copy of the schema was created with the name auth.schema.before. This happened because we passed the optional second parameter to MDB_Manager::updateDatabase(). In the next section we will see why this copy is created. 我们现在有了一个新的名字叫 auth 的数据库，它有一个表叫 users。在域 user_id 有一个索引。而且在表中还有一行。我们还有一个序列称为 users_user_id，它将被初始化为 1。因此序列中的下一个值就是 2。最后，schema 的一个拷贝以名字auth.schema.before 被创建。这是因为我们给 MDB_Manger::updateDatabase() 传递了可选的第二个参数。在下一节我们将看到为什么要创建这个拷贝。 This is all fairly amazing but it gets better. It is often the case an application needs to be changed at some point. For example we may decide we want to change the name of the table from users to people. We also want to add a field called pwd to store the password field (please check the textbox Reserved Words). Reserved Words The reason we do not call the field password is that this is a reserved word for field names in Interbase. Since we want to be RDBMS independent the MDB manager will either issue a warning or fail if the option fail_on_invalid_names is set to true (which is the default). In the old days you would now be in a bit of pain to alter all your existing installations to this new schema. But thanks to MDB this can be automated. In listing 5 are the changes we make to our table definition: Listing 5 <table> Now we want the manager to make the necessary alterations, but before I want to mention a possible pitfall. Since we renamed the table users to people we also have to change all references to the old name like in the sequence we build. There the reference in the on tag needs to be changed to point to the people table. To achieve this we pass the new and the old version of the schema to the manager. This is why we created a .before file when we first called MDB_Manager: |
凌众科技专业提供服务器租用、服务器托管、企业邮局、虚拟主机等服务，公司网站：http://www.lingzhong.cn 为了给广大客户了解更多的技术信息，本技术文章收集来源于网络,凌众科技尊重文章作者的版权，如果有涉及你的版权有必要删除你的文章，请和我们联系。以上信息与文章正文是不可分割的一部分,如果您要转载本文章,请保留以上信息，谢谢! |
