Question

Is it possible to append two databases in rails application? For example, SQLite database is portable. I can download SQLite database from another server. When rails application starts, it mount the database. Can i append all the data from another database to existing database? May be SQLite provide a way for merging databases?

Answer 1

I’m not sure sure what did you mean saying “append databases in application”. But you can use 2 different (with different schemes) databases in your application. For example:

config/database.yml

development:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: project_dev
  pool: 5
  username: project
  password:

test:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: project_test
  pool: 5
  username: project
  password: 

sqlite:
  development:
    adapter: sqlite3
    database: db/development.project.db
    pool: 5
    timeout: 5000

  test:
    adapter: sqlite3
    database: db/test.project.db
    pool: 5
    timeout: 5000

Models:

Abstract model for all sqlite models;
uses connection ninja gem

class SqliteModel < ActiveRecord::Base
  self.abstract_class = true
  use_connection_ninja(:sqlite)
end

Sqlite model

class Book < SqliteModel
  set_table_name  :Books
  set_primary_key :BookID

  belongs_to  :volume,  :foreign_key => :VolumeID
  has_many :chapters,   :foreign_key => :BookID
end

Mysql model

class Highlight < ActiveRecord::Base
  # ...
end

You can even use associations between tables in different databases.

But if you was asking about using 2 databases with the same scheme(i.e. just different data), then my answer is no, it’s not possible(I can be wrong though). I think that is a question about replication, synchronization, backups or something similar – DB layer, not application.

Of course you can have 2 same tables in both databases, 2 models – one per database, and then just copy records from one to another. But Rails won’t do it automatically.