Question

在rails应用程序中，我的代码是纯ruby：

class LinkCreator
  attr_accessor :animal

  def initialize(animal:)
    @animal = animal
  end

  def call
    "something#{link_id}"
  end

  private

  def link_id
    connection.execute(sql_request).first.first
  end

  def sql_request
    "SELECT field FROM table WHERE field_id = '#{field_id}' LIMIT 1"
  end

  def field_id
    animal.field_id
  end

  def connection
    ActiveRecord::Base.establish_connection(
      adapter:  "mysql",
      host:     ENV["MYSQL_HOST"],
      username: ENV["MYSQL_USERNAME"],
      password: ENV["MYSQL_PASSWORD"],
      database: ENV["MYSQL_DB_NAME"]
    ).connection
  end
end

正如您所看到的，这不是一个模型，而只是一个简单的类。问题在于，更改了activerecord的连接，以及稍后在新连接上执行的其他请求。

是否可以仅在块中建立连接并返回旧连接。我知道我可以建立另一个连接，但这对性能非常不利。

Answer 1

如果您将所有数据库连接保留在database.yml

中，那就太好了

development:
  adapter: mysql2
  other stuff...

db_2:
  adapter: mysql2
  other stuff..

other_envs:
.....

然后创建一个类

class OtherDB < ActiveRecord::Base
  establish_connection(:db_2)
end

您可以从控制器访问

OtherDB.table_name = "table_name"
OtherDB.first

在此处查看我的博客http://imnithin.in/multiple-database.html

Answer 2

您可以在一个区块内执行一些查询。首先，定义一些扩展ActiveRecord的模块，如下所示。这是生产中用于更改每个请求的数据库连接以及临时切换数据库以在另一个数据库中执行某些查询的代码的一部分。

# RAILS_ROOT/lib/connection_switch.rb
module ConnectionSwitch
  def with_db(connection_spec_name)
    current_conf = ActiveRecord::Base.connection_config

    begin
      ActiveRecord::Base.establish_connection(db_configurations[connection_spec_name]).tap do
        Rails.logger.debug "\e[1;35m [ActiveRecord::Base switched database] \e[0m #{ActiveRecord::Base.connection.current_database}"
      end if database_changed?(connection_spec_name)

      yield
    ensure
      ActiveRecord::Base.establish_connection(current_conf).tap do
        Rails.logger.debug "\e[1;35m [ActiveRecord::Base switched database] \e[0m #{ActiveRecord::Base.connection.current_database}"
      end if database_changed?(connection_spec_name, current_conf)
    end

  end

  private
  def database_changed?(connection_spec_name, current_conf = nil)
    current_conf = ActiveRecord::Base.connection_config unless current_conf
    current_conf[:database] != db_configurations[connection_spec_name].try(:[], :database)
  end

  def db_configurations
    @db_config ||= begin
      file_name =  "#{Rails.root}/config/database.yml"
      if File.exists?(file_name) || File.symlink?(file_name)
        config ||= HashWithIndifferentAccess.new(YAML.load(ERB.new(File.read(file_name)).result))
      else
        config ||= HashWithIndifferentAccess.new
      end

      config
    end
  end
end
ActiveRecord.send :extend, ConnectionSwitch

现在您可以按如下方式使用它：

ActiveRecord.with_db("db_connection_name") do
  # some queries to another db
end

Answer 3

在activerecord/test/support/connection_helper.rb的Rails代码库中找到了最简短的例子，稍微适应了：

def with_another_db(another_db_config)
  original_connection = ActiveRecord::Base.remove_connection
  ActiveRecord::Base.establish_connection(another_db_config)
  yield
ensure
  ActiveRecord::Base.establish_connection(original_connection)
end

用法（假设您another_db:中有database.yml部分）：

with_another_db(ActiveRecord::Base.configurations['another_db']) do
    ActiveRecord::Base.connection.execute("SELECT 'Look ma, I have changed DB!';")
end

Answer 4

我使用Heroku＆＃39; DATABASE_URL中的环境变量连接到不同的数据库：

class Database
  def self.development!
    ActiveRecord::Base.establish_connection(:development)
  end

  def self.production!
    ActiveRecord::Base.establish_connection(ENV['PRODUCTION_DATABASE'])
  end

  def self.staging!
    ActiveRecord::Base.establish_connection(ENV['STAGING_DATABASE'])
  end
end

e.g：

Database.production!; puts User.all.map(&:name)
Database.staging!; puts User.all.map(&:name)

Answer 5

使用实例变量来存储连接可能会有所帮助。像这样：

def connection
  @connection ||= ActiveRecord::Base.establish_connection(
    adapter:  "mysql",
    host:     ENV["MYSQL_HOST"],
    username: ENV["MYSQL_USERNAME"],
    password: ENV["MYSQL_PASSWORD"],
    database: ENV["MYSQL_DB_NAME"]
  ).connection
end

这样就可以在将来的连接尝试中检索现有连接，而不是建立新连接。

Answer 6

如果要连接到postgres sql，可以使用pg ruby gem并将下面的代码添加到代码块中。

postgres = PG.connect :host => <host_name>, :port => <port>, :dbname => <database_name>, :user => <user>, :password => <password>
    tables = postgres.exec(query)

    tables.num_tuples.times do |i|
      print tables[i]
    end

要连接到块内的mysql db，请使用mysql2 ruby gem并在块内添加以下代码。

db = Mysql2::Client.new ActiveRecord::ConnectionAdapters::ConnectionSpecification::ConnectionUrlResolver.new(<database_url>).to_hash

    data = db.query(<<-SQL)
      select * from students
    SQL

    print data

Answer 7

尝试 active_record_slave 宝石：

Ruby gem: active_record_slave

仅在块中建立与另一个数据库的连接？

7 个答案: