method

establish_connection

v2.3.8 - Show latest stable - Class: ActiveRecord::Base

establish_connection(spec = nil)

public

Establishes the connection to the database. Accepts a hash as input where the :adapter key must be specified with the name of a database adapter (in lower-case) example for regular databases (MySQL, Postgresql, etc):

  ActiveRecord::Base.establish_connection(
    :adapter  => "mysql",
    :host     => "localhost",
    :username => "myuser",
    :password => "mypass",
    :database => "somedatabase"
  )

Example for SQLite database:

  ActiveRecord::Base.establish_connection(
    :adapter => "sqlite",
    :database  => "path/to/dbfile"
  )

Also accepts keys as strings (for parsing from YAML for example):

  ActiveRecord::Base.establish_connection(
    "adapter" => "sqlite",
    "database"  => "path/to/dbfile"
  )

The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError may be returned on an error.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 51
    def self.establish_connection(spec = nil)
      case spec
        when nil
          raise AdapterNotSpecified unless defined? RAILS_ENV
          establish_connection(RAILS_ENV)
        when ConnectionSpecification
          self.connection_handler.establish_connection(name, spec)
        when Symbol, String
          if configuration = configurations[spec.to_s]
            establish_connection(configuration)
          else
            raise AdapterNotSpecified, "#{spec} database is not configured"
          end
        else
          spec = spec.symbolize_keys
          unless spec.key?(:adapter) then raise AdapterNotSpecified, "database configuration does not specify adapter" end

          begin
            require 'rubygems'
            gem "activerecord-#{spec[:adapter]}-adapter"
            require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
          rescue LoadError
            begin
              require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
            rescue LoadError
              raise "Please install the #{spec[:adapter]} adapter: `gem install activerecord-#{spec[:adapter]}-adapter` (#{$!})"
            end
          end

          adapter_method = "#{spec[:adapter]}_connection"
          if !respond_to?(adapter_method)
            raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter"
          end

          remove_connection
          establish_connection(ConnectionSpecification.new(spec, adapter_method))
      end
    end

1Note

Connections to multiple databases

GavinLaking · Jul 3, 20085 thanks

establish_connection can be used to connect to multiple databases. The immediate downside is that your rake migrations may not work properly without hacking.

In each model that resides in a different database we call:

establish_connection :different_database

You can check they are working by hitting script/console with:

App.connection.instance_eval {@config[:database]} => "app_development"

AnotherDatabase.connection.instance_eval {@config[:database]} => "another_database"

Now doing a call to AnotherDatabase.find() will connect to the AnotherDatabase database and start returning results.

establish_connection

1Note

Connections to multiple databases

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