具有DB2和多个模式的Rails

Question

I have a 'legacy' DB2 database that has many other applications and users. Trying to experiment with a rails app. Got everything working great with the ibm_db driver.

Problem is that I have some tables like schema1.products, schema1.sales and other tables like schema2.employees and schema2.payroll.

In the ibm_db adapter connection, I specify a schema, like schema1 or schema2, and I can work within that one schema, but I need to be able to easily (and transparently) reference both schemas basically interchangeably. I don't want to break the other apps, and the SQL I would normally write against DB2 doesn't have any of these restrictions (schemas can be mixed in SQL against DB2 without any trouble at all).

I would like to just specify table names as "schema1.products" for example and be done with it, but that doesn't seem to jive with the "rails way" of going about it.

Suggestions?

Answer 1

如何在具有活动记录的Rails中使用两个不同的数据库？

Answer 2

Schemas in DB2 are a very handy way to provide separate namespace to different applications. For example, you can separate all database objects for an application called "recruiting" from say application called "payroll". You can have objects (tables, views, procedures etc.) with the same name reside in multiple schemas and not colide with one another. Having your application set a schema is a handy way for it to say "hey, I am a payroll and I only want to work with my objects". So, what happens when you want to work with objects owned by another application? Well, in traditional procedural programming languages your application code would explicitly specify the schema when referencing an object in another schema or you would just do a SET CURRENT SCHEMA to switch to another schema. The problem with ORMs like ActiveRecord in Ruby on Rails is that you are not supposed to use SQL ie you don't have a good "Rails way" to specify schema when referencing an object. You can use find_by_sql and qualify your objects in the SQL statement but this is not what RoR people will consider to be good Rails. You can fix things on the DB2 side. You can define a view per table in the "foreign" schema but you will have to take care to name the view so that it does not colide with what you already have in your primary schema. And, when you do that, you will undoubtedly create names that are not true Rails names. Rails people are very proud of the "Rails way". It makes it very easy to create new applications. Rails is really awesome in this space. However, when it comes to integration with what is already out there Rails ... how do we say it ... sucks. I suggest you will have to accept to do things that are not the best examples of the Rails Way if you want to work with existing database structures.