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Class: ActiveRecord::ConnectionAdapters::ConnectionHandler

Relationships & Source Files
Namespace Children
Classes:
ConnectionDescriptor
Inherits: Object
Defined in: activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb

Overview

Active Record Connection Handler

ConnectionHandler is a collection of ConnectionPool objects. It is used for keeping separate connection pools that connect to different databases.

For example, suppose that you have 5 models, with the following hierarchy:

class Author < ActiveRecord::Base
end

class BankAccount < ActiveRecord::Base
end

class Book < ActiveRecord::Base
  establish_connection :library_db
end

class ScaryBook < Book
end

class GoodBook < Book
end

And a database.yml that looked like this:

development:
  database: my_application
  host: localhost

library_db:
  database: library
  host: some.library.org

Your primary database in the development environment is “my_application” but the Book model connects to a separate database called “library_db” (this can even be a database on a different machine).

Book, ScaryBook, and GoodBook will all use the same connection pool to “library_db” while Author, BankAccount, and any other models you create will use the default connection pool to “my_application”.

The various connection pools are managed by a single instance of ConnectionHandler accessible via Base.connection_handler. All Active Record models use this handler to determine the connection pool that they should use.

The ConnectionHandler class is not coupled with the Active models, as it has no knowledge about the model. The model needs to pass a connection specification name to the handler, in order to look up the correct connection pool.

Class Method Summary

Instance Attribute Summary

Instance Method Summary

Constructor Details

.new ⇒ ConnectionHandler

[ GitHub ] 

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 76



def initialize
  # These caches are keyed by pool_config.connection_name (PoolConfig#connection_name).
  @connection_name_to_pool_manager = Concurrent::Map.new(initial_capacity: 2)
end


  







Instance Attribute Details



  

    #connection_name_to_pool_manager   (readonly, private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 240



attr_reader :connection_name_to_pool_manager


  








  

    #prevent_writes   (rw)
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 81



def prevent_writes # :nodoc:
  ActiveSupport::IsolatedExecutionState[:active_record_prevent_writes]
end


  








  

    #prevent_writes=(prevent_writes)   (rw)
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 85



def prevent_writes=(prevent_writes) # :nodoc:
  ActiveSupport::IsolatedExecutionState[:active_record_prevent_writes] = prevent_writes
end


  







Instance Method Details



  

    #active_connections?(role = nil)  ⇒ Boolean 
  



  

    

Returns true if there are any active connections among the connection pools that the ConnectionHandler is managing.


  





  


  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 157



def active_connections?(role = nil)
  each_connection_pool(role).any?(&:active_connection?)
end


  








  

    #clear_active_connections!(role = nil)  
  



  

    

Returns any connections in use by the current thread back to the pool, and also returns connections to the pool cached by threads that are no longer alive.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 164



def clear_active_connections!(role = nil)
  each_connection_pool(role).each do |pool|
    pool.release_connection
    pool.disable_query_cache!
  end
end


  








  

    #clear_all_connections!(role = nil)  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 178



def clear_all_connections!(role = nil)
  each_connection_pool(role).each(&:disconnect!)
end


  








  

    #clear_reloadable_connections!(role = nil)  
  



  

    

Clears the cache which maps classes.



See ConnectionPool#clear_reloadable_connections! for details.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 174



def clear_reloadable_connections!(role = nil)
  each_connection_pool(role).each(&:clear_reloadable_connections!)
end


  








  

    #connected?(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)  ⇒ Boolean 
  



  

    

Returns true if a connection that’s accessible to this class has already been opened.


  





  


  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 200



def connected?(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  pool = retrieve_connection_pool(connection_name, role: role, shard: shard)
  pool && pool.connected?
end


  








  

    #connection_pool_list(role = nil)  
    Also known as: #connection_pools
  



  

    

Returns the pools for a connection handler and given role. If :all is passed, all pools belonging to the connection handler will be returned.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 95



def connection_pool_list(role = nil)
  if role.nil? || role == :all
    connection_name_to_pool_manager.values.flat_map { |m| m.pool_configs.map(&:pool) }
  else
    connection_name_to_pool_manager.values.flat_map { |m| m.pool_configs(role).map(&:pool) }
  end
end


  








  

    #connection_pool_names  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 89



def connection_pool_names # :nodoc:
  connection_name_to_pool_manager.keys
end


  








  

    #connection_pools(role = nil)  
  



  

    

Alias for #connection_pool_list.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 102



alias :connection_pools :connection_pool_list


  








  

    #determine_owner_name(owner_name, config)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 282



def determine_owner_name(owner_name, config)
  if owner_name.is_a?(String) || owner_name.is_a?(Symbol)
    ConnectionDescriptor.new(owner_name.to_s)
  elsif config.is_a?(Symbol)
    ConnectionDescriptor.new(config.to_s)
  else
    owner_name
  end
end


  








  

    #disconnect_pool_from_pool_manager(pool_manager, role, shard)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 256



def disconnect_pool_from_pool_manager(pool_manager, role, shard)
  pool_config = pool_manager.remove_pool_config(role, shard)

  if pool_config
    pool_config.disconnect!
    pool_config.db_config
  end
end


  








  

    #each_connection_pool(role = nil, &block)  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 104



def each_connection_pool(role = nil, &block) # :nodoc:
  role = nil if role == :all
  return enum_for(__method__, role) unless block_given?

  connection_name_to_pool_manager.each_value do |manager|
    manager.each_pool_config(role) do |pool_config|
      yield pool_config.pool
    end
  end
end


  








  

    #establish_connection(config, owner_name: Base, role: Base.current_role, shard: Base.current_shard, clobber: false)  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 115



def establish_connection(config, owner_name: Base, role: Base.current_role, shard: Base.current_shard, clobber: false)
  owner_name = determine_owner_name(owner_name, config)

  pool_config = resolve_pool_config(config, owner_name, role, shard)
  db_config = pool_config.db_config

  pool_manager = set_pool_manager(pool_config.connection_descriptor)

  # If there is an existing pool with the same values as the pool_config
  # don't remove the connection. Connections should only be removed if we are
  # establishing a connection on a class that is already connected to a different
  # configuration.
  existing_pool_config = pool_manager.get_pool_config(role, shard)

  if !clobber && existing_pool_config && existing_pool_config.db_config == db_config
    # Update the pool_config's connection class if it differs. This is used
    # for ensuring that ActiveRecord::Base and the primary_abstract_class use
    # the same pool. Without this granular swapping will not work correctly.
    if owner_name.primary_class? && (existing_pool_config.connection_descriptor != owner_name)
      existing_pool_config.connection_descriptor = owner_name
    end

    existing_pool_config.pool
  else
    disconnect_pool_from_pool_manager(pool_manager, role, shard)
    pool_manager.set_pool_config(role, shard, pool_config)

    payload = {
      connection_name: pool_config.connection_descriptor.name,
      role: role,
      shard: shard,
      config: db_config.configuration_hash
    }

    ActiveSupport::Notifications.instrumenter.instrument("!connection.active_record", payload) do
      pool_config.pool
    end
  end
end


  








  

    #flush_idle_connections!(role = nil)  
  



  

    

Disconnects all currently idle connections.



See ConnectionPool#flush! for details.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 185



def flush_idle_connections!(role = nil)
  each_connection_pool(role).each(&:flush!)
end


  








  

    #get_pool_manager(connection_name)   (private)
  



  

    

Returns the pool manager for a connection name / identifier.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 243



def get_pool_manager(connection_name)
  connection_name_to_pool_manager[connection_name]
end


  








  

    #pool_managers   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 252



def pool_managers
  connection_name_to_pool_manager.values
end


  








  

    #remove_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 205



def remove_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  if pool_manager = get_pool_manager(connection_name)
    disconnect_pool_from_pool_manager(pool_manager, role, shard)
  end
end


  








  

    #resolve_pool_config(config, connection_name, role, shard)   (private)
  



  

    

Returns an instance of PoolConfig for a given adapter. Accepts a hash one layer deep that contains all connection information.



Example



config = { "production" => { "host" => "localhost", "database" => "foo", "adapter" => "sqlite3" } }
pool_config = Base.configurations.resolve_pool_config(:production)
pool_config.db_config.configuration_hash
# => { host: "localhost", database: "foo", adapter: "sqlite3" }


  





  
Raises:





  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 275



def resolve_pool_config(config, connection_name, role, shard)
  db_config = Base.configurations.resolve(config)
  db_config.validate!
  raise(AdapterNotSpecified, "database configuration does not specify adapter") unless db_config.adapter
  ConnectionAdapters::PoolConfig.new(connection_name, db_config, role, shard)
end


  








  

    #retrieve_connection(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)  
  

  

    This method is for internal use only.
  



  

    

Locate the connection of the nearest super class. This can be an active or defined connection: if it is the latter, it will be opened and set as the active connection for the class it was defined for (not necessarily the current class).


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 193



def retrieve_connection(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) # :nodoc:
  pool = retrieve_connection_pool(connection_name, role: role, shard: shard, strict: true)
  pool.lease_connection
end


  








  

    #retrieve_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard, strict: false)  
  



  

    

Retrieving the connection pool happens a lot, so we cache it in @connection_name_to_pool_manager. This makes retrieving the connection pool O(1) once the process is warm. When a connection is established or removed, we invalidate the cache.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 214



def retrieve_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard, strict: false)
  pool_manager = get_pool_manager(connection_name)
  pool = pool_manager&.get_pool_config(role, shard)&.pool

  if strict && !pool
    selector = [
      ("'#{shard}' shard" unless shard == ActiveRecord::Base.default_shard),
      ("'#{role}' role" unless role == ActiveRecord::Base.default_role),
    ].compact.join(" and ")

    selector = [
      (connection_name unless connection_name == "ActiveRecord::Base"),
      selector.presence,
    ].compact.join(" with ")

    selector = " for #{selector}" if selector.present?

    message = "No database connection defined#{selector}."

    raise ConnectionNotDefined.new(message, connection_name: connection_name, shard: shard, role: role)
  end

  pool
end


  








  

    #set_pool_manager(connection_descriptor)   (private)
  



  

    

Get the existing pool manager or initialize and assign a new one.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 248



def set_pool_manager(connection_descriptor)
  connection_name_to_pool_manager[connection_descriptor.name] ||= PoolManager.new
end