I'm refactoring some features of a legacy php application which uses multiple databases with the same structure, one per language. When an user login choose his language and then all the following connections are made with the db for that app with some code like this:
$db_name = 'db_appname_' . $_SESSION['language'];
mysql_connect(...);
mysql_select_db($db_name);
I'd like to refactor also the database, but currently it's not an option because other pieces of software should remain in production with the old structure while the new app is developed, and for some time after it's been developed.
I saw this question, but both the question and the suggested gems are pretty old and it seems that they are not working with Rails 3.
Which is the best method to achieve this behavior in my new rails 3 app? Is there any other choice that avoid me to alter the db structure and fits my needs?
Last detail: in the php app even the login information are kept in separate tables, i.e. every db has its own users table and when the user logs in it also passes a language param in the login form. I'd like to use devise for auth in the new app which likely won't work with this approach, so I'm thinking to duplicate (I know, this is not DRY) login information in a separate User model with a language attribute and a separate db shared among languages to use devise features with my app. Will this cause any issue?
EDIT:
For completeness, I ended with this yml configuration file
production: &production
adapter: mysql
host: localhost
username: user
password: secret
timeout: 5000
production_italian:
<<: *production
database: db_app_ita
production_english:
<<: *production
database: db_app_eng
and with this config in base model (actually not exactly this but this is for keeping things clear)
MyModel < AR::Base
establish_connection "production_#{session[:language]}"
...
end
use establish_connection in your models:
MyModel < AR::Base
establish_connection "db_appname_#{session[:language]}"
...
end
Use MultiConfig gem I created to make this easy.
You could specify the configs in separate file like database_italian.yml etc and then call:
ActiveRecord::Base.config_file = 'database_italian'
This way it will be much easier to maintain and cleaner looking. Just add more language db config files as you wish
Related
I'll try to keep this as brief as possible and open the question to discussion.
I have a Rails app which is a static codebase and runs on 9 different servers all the same db schema but of course with different values.
I wrote some SQL to query some dollar totals and will be putting this into either a rake task or a sidekiq worker and have it fire once a week to generate the data. Initially I was thinking of just throwing the resulting data from each server into a mailer and mailing it to whoever needs the data. This is pretty straight forward.
But there's a kink in this, we need to see metrics over time in highcharts or some other charting engine.
So here's my thought.
Create the sidekiq worker and fire it on a schedule
Take the resulting data from each server and populate it on a target server via Postgres (not sure how to do this)
The target server will have a very simple Rails app built that will have a model with metrics and an association for each server (ie server 1 server 2 etc), after populating the data via postgres (somehow) from the source servers, read the data in HighCharts and present the view
So that's my thought process so far. I'm not sure on how to get the data from the source servers via a live postgres call when the sidekiq worker fires. So that's problem #1. Problem #2 or more like question #2 is, would this be a better use case for creating some sort of consumable API on the target Rails server? If so, what's the best place to start.
If my question and thought process is unclear, please let me know so I can clarify and explain in better detail.
Cheers!
There are plenty of tutorials on how to use multiple database connections in Rails as well as building an API in Rails. A few minutes of Googling will give you plenty of examples. But here are a couple barebones approaches:
For multiple database connections, you are right, you'll need to have the connection info for both databases defined in your database.yml file. Example:
# Local Database
development:
adapter: mysql2
database: local_db
username: my_user
password: my_password
host: localhost
port: 3306
# Reporting Database
development_reporting_db:
adapter: postgresql
encoding: unicode
database: reporting
username: some_user
password: some_password
host: 1.2.3.4
port: 5432
Rails won't do anything with this extra block though unless you explicitly tell it to. The common practice is to define an abstract ActiveRecord model that will establish the second connection:
class ReportingRecord < ActiveRecord::Base
establish_connection( "#{Rails.env}_reporting_db".to_sym )
self.abstract_class = true
end
Then, create new models for tables that reside in your reporting database and inherit from ReportingRecord instead of ActiveRecord::Base:
class SomeModel < ReportingRecord
# this model sits on top of a table defined in database.yml --> development_reporting_db instead of database.yml --> development
end
For building an API, there are tons of different ways to do it. Regardless of your approach, I'd highly suggest you make sure it's only accessible via HTTPS. Here's a basic controller with one action that responds to json requests:
class ApiController < ApplicationController
before_filter :restrict_access # ensures the correct api token was passed (defined in config/secrets.yml)
skip_before_action :verify_authenticity_token # not needed since we're using token restriction
respond_to :json
def my_endpoint_action
render :json => {some_info: 'Hello World'}, :status => 200 # 200 = success
end
private
rescue_from StandardError do |e|
render :json => {:error => e.message}.to_json, :status => 400 # 400 = bad request
end
# ensures the correct api token was passed (defined in config/secrets.yml)
def restrict_access
authenticate_or_request_with_http_token do |token, options|
token == Rails.application.secrets[:my_access_token]
end
end
end
This example would require you to define an access token in your config/secrets.yml file:
development:
secret_key_base: # normal Rails secret key base
my_api_access_token: # put a token here (you can generate one on the command like using rake secret)
Choosing between an API and a multiple DB solution depends mostly on how your application might expand in the future. The multiple DB approach is typically easier to implement and has higher performance. An API tends to scale horizontally better and databases that have a connection from only one application instead of 2 or more tend to be easier to maintain over time.
Hope this helps!
I'm on the early stages on learning Ruby.I really don't have an idea on how to use an existing database filled with tables and data on ruby. Every guide, every article that I have or find on the internet is always creating a new one using the migration functions.
But which are the steps for using an existing database in SQL server on RoR?
You're in luck, friend. My first Rails project (7 years ago) was against a horribly set up SQL Server database.
Per the above, you need to set up your database.yml appropriately. But for an existing database, obviously it is unlikely that the table and column names conform to the Rails conventions. The good news is that you can override all of those defaults. Here is a non-exhaustive list of those directives:
In a model descended from AR::Base,
set_table_name 'actual_table_name'
set_primary_key 'actual_primary_key_name'
On the various association directives (has_one, has_many, belongs_to), there are :foreign_key keys that let you specify the name of the foreign keys.
Now, one of the things that MS SQL Server allows you to do which is TERRIBLE is that you can embed spaces into your column names. Fear not, you can still refer to these columns by name using write_attribute("badly named column") and read_attribute("badly named column"). You may also refer to them in various directives like so:
validates_length_of "Fax Number", :maximum => 17, :allow_nil => true
Finally, you may refer to the implied methods these devilishly named columns generate like so:
self.send('Fax Number=', new_fax_number)
Obviously, you can't refer to them as symbols, since spaces are disallowed in Ruby symbols.
Good luck, and next time I hope that you get to work with a real RDBMS, like Informix :).
First you have to setup your application to user sql server for databases connectivity.
you have to use gem for sql server in your gemfile and have to setup database.yml file accordingly.
In database.yml, in config folder put the name of same database In the Development part of this file.
development:
adapter:
database: db_name_dev
username:
password:
host: localhost
socket:
To use a existing server. In your database.yml you have to specify the host, port and the database name.
`database: <host>:<port>/<database_name>`
For eg
development:
adapter: mysql2
database: your.mysqlserver.com:1521/project_database
username: project_user
password: project_password
Can this be done? In a single application, that manages many projects with SQLite.
What I want is to have a different database for each project my app is managing.. so multiple copies of an identically structured database, but with different data in them. I'll be choosing which copy to use base on params on the URI.
This is done for 1. security.. I'm a newbe in this kind of programming and I don't want it to happen that for some reason while working on a Project another one gets corrupted.. 2. easy backup and archive of old projects
Rails by default is not designed for a multi-database architecture and, in most cases, it doesn't make sense at all.
But yes, you can use different databases and connections.
Here's some references:
ActiveRecord: Connection to multiple databases in different models
Multiple Database Connections in Ruby on Rails
Magic Multi-Connections
If you are able to control and configure each Rails instance, and you can afford wasting resources because of them being on standby, save yourself some trouble and just change the database.yml to modify the database connection used on every instance. If you are concerned about performance this approach won't cut it.
For models bound to a single unique table on only one database you can call establish_connection inside the model:
establish_connection "database_name_#{RAILS_ENV}"
As described here: http://apidock.com/rails/ActiveRecord/Base/establish_connection/class
You will have some models using tables from one database and other different models using tables from other databases.
If you have identical tables, common on different databases, and shared by a single model, ActiveRecord won't help you. Back in 2009 I required this on a project I was working on, using Rails 2.3.8. I had a database for each customer, and I named the databases with their IDs. So I created a method to change the connection inside ApplicationController:
def change_database database_id = params[:company_id]
return if database_id.blank?
configuration = ActiveRecord::Base.connection.instance_eval { #config }.clone
configuration[:database] = "database_name_#{database_id}_#{RAILS_ENV}"
MultipleDatabaseModel.establish_connection configuration
end
And added that method as a before_filter to all controllers:
before_filter :change_database
So for each action of each controller, when params[:company_id] is defined and set, it will change the database to the correct one.
To handle migrations I extended ActiveRecord::Migration, with a method that looks for all the customers and iterates a block with each ID:
class ActiveRecord::Migration
def self.using_databases *args
configuration = ActiveRecord::Base.connection.instance_eval { #config }
former_database = configuration[:database]
companies = args.blank? ? Company.all : Company.find(args)
companies.each do |company|
configuration[:database] = "database_name_#{company[:id]}_#{RAILS_ENV}"
ActiveRecord::Base.establish_connection configuration
yield self
end
configuration[:database] = former_database
ActiveRecord::Base.establish_connection configuration
end
end
Note that by doing this, it would be impossible for you to make queries within the same action from two different databases. You can call change_database again but it will get nasty when you try using methods that execute queries, from the objects no longer linked to the correct database. Also, it is obvious you won't be able to join tables that belong to different databases.
To handle this properly, ActiveRecord should be considerably extended. There should be a plugin by now to help you with this issue. A quick research gave me this one:
DB-Charmer: http://kovyrin.github.com/db-charmer/
I'm willing to try it. Let me know what works for you.
I got past this by adding this to the top of my models using the other database
class Customer < ActiveRecord::Base
ENV["RAILS_ENV"] == "development" ? host = 'devhost' : host = 'prodhost'
self.establish_connection(
:adapter => "mysql",
:host => "localhost",
:username => "myuser",
:password => "mypass",
:database => "somedatabase"
)
You should also check out this project called DB Charmer:
http://kovyrin.net/2009/11/03/db-charmer-activerecord-connection-magic-plugin/
DbCharmer is a simple yet powerful plugin for ActiveRecord that does a few things:
Allows you to easily manage AR models’ connections (switch_connection_to method)
Allows you to switch AR models’ default connections to a separate servers/databases
Allows you to easily choose where your query should go (on_* methods family)
Allows you to automatically send read queries to your slaves while masters would handle all the updates.
Adds multiple databases migrations to ActiveRecord
It's worth noting, in all these solutions you need to remember to close custom database connections. You will run out of connections and see weird request timeout issues otherwise.
An easy solution is to clear_active_connections! in an after_filter in your controller.
after_filter :close_custom_db_connection
def close_custom_db_connection
MyModelWithACustomDBConnection.clear_active_connections!
end
in your config/database.yml do something like this
default: &default
adapter: postgresql
encoding: unicode
pool: 5
development:
<<: *default
database: mysite_development
test:
<<: *default
database: mysite_test
production:
<<: *default
host: 10.0.1.55
database: mysite_production
username: postgres_user
password: <%= ENV['DATABASE_PASSWORD'] %>
db2_development:
<<: *default
database: db2_development
db2_test:
<<: *default
database: db2_test
db2_production:
<<: *default
host: 10.0.1.55
database: db2_production
username: postgres_user
password: <%= ENV['DATABASE_PASSWORD'] %>
then in your models you can reference db2 with
class Customers < ActiveRecord::Base
establish_connection "db2_#{Rails.env}".to_sym
end
What you've described in the question is multitenancy (identically structured databases with different data in each). The Apartment gem is great for this.
For the general question of multiple databases in Rails: ActiveRecord supports multiple databases, but Rails doesn’t provide a way to manage them. I recently created the Multiverse gem to address this.
The best solution I have found so far is this:
There are 3 database architectures that we can approach.
Single Database for Single Tenant
Separate Schema for Each Tenant
Shared Schema for Tenants
Note: they have certain pros and cons depends on your use case.
I got this from this Blog! Stands very helpful for me.
You can use the gem Apartment for rails
Video reference you may follow at Gorails for apartment
As of Rails 6, multiple databases are supported: https://guides.rubyonrails.org/active_record_multiple_databases.html#generators-and-migrations
Sorry for the late and obvious answer, but figured it's viable since it's supported now.
I have a Rails project which has a Postgres database for the actual application but which needs to pull a heck of a lot of data out of an Oracle database.
database.yml looks like
development:
adapter: postgresql
database: blah blah
...
oracle_db:
adapter: oracle
database: blah blah
My models which descend from data on the Oracle DB look something like
class LegacyDataClass < ActiveRecord::Base
establish_connection "oracle_db"
set_primary_key :legacy_data_class_id
has_one :other_legacy_class, :foreign key => :other_legacy_class_id_with_funny_column_name
...
end
Now, by habit I often do a lot of my early development (and this is early development) by coding for a bit and then playing in the Rails console. For example, after defining all the associations for LegacyDataClass I'll start trying things like a = LegacyDataClass.find(:first); puts a.some_association.name. Unexpectedly, this dies with LegacyDataClass not being already loaded.
I can then require 'LegacyDataClass' which fixes the problem until I either need to reload!, which won't actually reload it, or until I open a new instance of the console.
Thus the questions:
Why does this happen? Clearly there is some Rails magic I am not understanding.
What is the convenient Rails workaround?
I believe this might have to do with your model name, rather than your connection. The Rails convention is that model class names are CamelCase, while the files they reside in are lowercase+underscore.
The "LegacyModel" class should therefore be in models/legacy_model.rb. Your statement about "require 'LegacyDataClass'" indicates that this is not the case, and therefore Rails doesn't know how to automagically load that model.
I wrote something for an app at work that handles connections to other databases' at runtime, it might be able to help.
http://github.com/cherring/connection_ninja
What's the best way to deal with a sharded database in Rails? Should the sharding be handled at the application layer, the active record layer, the database driver layer, a proxy layer, or something else altogether? What are the pros and cons of each?
FiveRuns have a gem named DataFabric that does application-level sharding and master/slave replication. It might be worth checking out.
I assume with shards we're talking about horizontal partitioning and not vertical partitioning (here are the differences on Wikipedia).
First off, stretch vertical partitioning as far as you can take it before you consider horizontal partitioning. It's easy in Rails to have different models point to different machines and for most Rails sites, this will bring you far enough.
For horizontal partitioning, in an ideal world, this would be handled at the application layer in Rails. But while it's not hard, it's not trivial in Rails, and by the time you need it, usually your application has grown beyond the point where this is feasible since you have ActiveRecord calls sprinkled all over the place. And no one, developers or management, likes working on it before you need it since everyone would rather work on features users will use now rather than on partitioning which may not come into play for years after your traffic has exploded.
ActiveRecord layer... not easy from what I can see. Would require lots of monkey patching into Rails internals.
At Spock we ended up handling this using a custom MySQL proxy and open sourced it on SourceForge as Spock Proxy. ActiveRecord thinks it's talking to one MySQL database machine when reality it's talking to the proxy, which then talks to one or more MySQL databases, merges/sorts the results, and returns them to ActiveRecord. Requires only a few changes to your Rails code. Take a look at the Spock Proxy SourceForge page for more details and for our reasons for going this route.
For those of you like me who hadn't heard of sharding:
http://highscalability.com/unorthodox-approach-database-design-coming-shard
rails 6.1 provides ability to switch connection per database thus we can do the horizontal partitioning.
Shards are declared in the three-tier config like this:
production:
primary:
database: my_primary_database
adapter: mysql2
primary_replica:
database: my_primary_database
adapter: mysql2
replica: true
primary_shard_one:
database: my_primary_shard_one
adapter: mysql2
primary_shard_one_replica:
database: my_primary_shard_one
adapter: mysql2
replica: true
Models are then connected with the connects_to API via the shards key
class ApplicationRecord < ActiveRecord::Base
self.abstract_class = true
connects_to shards: {
default: { writing: :primary, reading: :primary_replica },
shard_one: { writing: :primary_shard_one, reading: :primary_shard_one_replica }
}
end
Then models can swap connections manually via the connected_to API. If using sharding, both a role and a shard must be passed:
ActiveRecord::Base.connected_to(role: :writing, shard: :shard_one) do
#id = Person.create! # Creates a record in shard one
end
ActiveRecord::Base.connected_to(role: :writing, shard: :shard_one) do
Person.find(#id) # Can't find record, doesn't exist because it was created
# in the default shard
end
reference:
https://edgeguides.rubyonrails.org/active_record_multiple_databases.html#horizontal-sharding
https://dev.to/ritikesh/multitenant-architecture-on-rails-6-1-27c7
Connecting Rails to multiple databases is not a big deal- you simply have an ActiveRecord subclass for each shard that overrides the connection property. That makes it pretty simple if you need to make cross-shard calls. You then just have to write a little code when you need to make calls between the shards.
I don't like Hank's idea of splitting the rails instances, because it seems challenging to call the code between the instances unless you have a big shared library.
Also you should look at doing something like Masochism before you start sharding.
For rails to work with replicated environment, I would suggest using my_replication plugin which helps switch database connection to one of the slaves at run-time
https://github.com/minhnghivn/my_replication
To my mind, the simplest way is maintain a 1:1 between rails instances and DB shards.
Proxy layer is better, it can support all program languages.
For example: Apache ShardingSphere' proxy.
There are 2 different products of Apache ShardingSphere, ShardingSphere-JDBC for application layer which for Java language only and ShardingSphere-Proxy for proxy layer which for all program languages.
FYI: https://shardingsphere.apache.org/document/current/en/user-manual/shardingsphere-proxy/
Depends upon rails version. Newer rails version provide support for sharding as said by #Oshan. But if you can't update to a newer version you can use the octopus gem.
Gem Link
https://github.com/thiagopradi/octopus