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Class: ActiveRecord::ConnectionAdapters::ConnectionHandler

Relationships & Source Files
Namespace Children
Classes:
StringConnectionName
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.

Constant Summary

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 77



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)

  # Backup finalizer: if the forked child skipped Kernel#fork the early discard has not occurred
  ObjectSpace.define_finalizer self, FINALIZER
end


  







Instance Attribute Details



  

    #connection_name_to_pool_manager   (readonly, private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 271



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 85



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 89



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 173



def active_connections?(role = nil)
  if role.nil?
    deprecation_for_pool_handling(__method__)
    role = ActiveRecord::Base.current_role
  end

  each_connection_pool(role).any?(&:active_connection?)
end


  








  

    #all_connection_pools  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 97



def all_connection_pools
  ActiveRecord.deprecator.warn(<<-MSG.squish)
    The `all_connection_pools` method is deprecated in favor of `connection_pool_list`.
    Call `connection_pool_list(:all)` to get the same behavior as `all_connection_pools`.
  MSG
  connection_name_to_pool_manager.values.flat_map { |m| m.pool_configs.map(&:pool) }
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 185



def clear_active_connections!(role = nil)
  if role.nil?
    deprecation_for_pool_handling(__method__)
    role = ActiveRecord::Base.current_role
  end

  each_connection_pool(role).each(&:release_connection)
end


  








  

    #clear_all_connections!(role = nil)  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 206



def clear_all_connections!(role = nil)
  if role.nil?
    deprecation_for_pool_handling(__method__)
    role = ActiveRecord::Base.current_role
  end

  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 197



def clear_reloadable_connections!(role = nil)
  if role.nil?
    deprecation_for_pool_handling(__method__)
    role = ActiveRecord::Base.current_role
  end

  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 251



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 107



def connection_pool_list(role = nil)
  if role.nil?
    deprecation_for_pool_handling(__method__)
    role = ActiveRecord::Base.current_role
    connection_name_to_pool_manager.values.flat_map { |m| m.pool_configs(role).map(&:pool) }
  elsif 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 93



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 118



alias :connection_pools :connection_pool_list


  








  

    #deprecation_for_pool_handling(method)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 287



def deprecation_for_pool_handling(method)
  roles = []
  pool_managers.each do |pool_manager|
    roles << pool_manager.role_names
  end

  if roles.flatten.uniq.count > 1
    ActiveRecord.deprecator.warn(<<-MSG.squish)
      `#{method}` currently only applies to connection pools in the current
      role (`#{ActiveRecord::Base.current_role}`). In Rails 7.2, this method
      will apply to all known pools, regardless of role. To affect only those
      connections belonging to a specific role, pass the role name as an
      argument. To switch to the new behavior, pass `:all` as the role name.
    MSG
  end
end


  








  

    #determine_owner_name(owner_name, config)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb', line 356



def determine_owner_name(owner_name, config)
  if owner_name.is_a?(String) || owner_name.is_a?(Symbol)
    StringConnectionName.new(owner_name.to_s)
  elsif config.is_a?(Symbol)
    StringConnectionName.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 304



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 120



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 131



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_name)

  # 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_class != owner_name)
      existing_pool_config.connection_class = 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_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 218



def flush_idle_connections!(role = nil)
  if role.nil?
    deprecation_for_pool_handling(__method__)
    role = ActiveRecord::Base.current_role
  end

  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 274



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 283



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 256



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 323



def resolve_pool_config(config, connection_name, role, shard)
  db_config = Base.configurations.resolve(config)

  raise(AdapterNotSpecified, "database configuration does not specify adapter") unless db_config.adapter

  # Require the adapter itself and give useful feedback about
  #   1. Missing adapter gems and
  #   2. Adapter gems' missing dependencies.
  path_to_adapter = "active_record/connection_adapters/#{db_config.adapter}_adapter"
  begin
    require path_to_adapter
  rescue LoadError => e
    # We couldn't require the adapter itself. Raise an exception that
    # points out config typos and missing gems.
    if e.path == path_to_adapter
      # We can assume that a non-builtin adapter was specified, so it's
      # either misspelled or missing from Gemfile.
      raise LoadError, "Could not load the '#{db_config.adapter}' Active Record adapter. Ensure that the adapter is spelled correctly in config/database.yml and that you've added the necessary adapter gem to your Gemfile.", e.backtrace

      # Bubbled up from the adapter require. Prefix the exception message
      # with some guidance about how to address it and reraise.
    else
      raise LoadError, "Error loading the '#{db_config.adapter}' Active Record adapter. Missing a gem it depends on? #{e.message}", e.backtrace
    end
  end

  unless ActiveRecord::Base.respond_to?(db_config.adapter_method)
    raise AdapterNotFound, "database configuration specifies nonexistent #{db_config.adapter} adapter"
  end

  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 231



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)

  unless pool
    if shard != ActiveRecord::Base.default_shard
      message = "No connection pool for '#{connection_name}' found for the '#{shard}' shard."
    elsif role != ActiveRecord::Base.default_role
      message = "No connection pool for '#{connection_name}' found for the '#{role}' role."
    else
      message = "No connection pool for '#{connection_name}' found."
    end

    raise ConnectionNotEstablished, message
  end

  pool.connection
end


  








  

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



  

    

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 265



def retrieve_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  pool_config = get_pool_manager(connection_name)&.get_pool_config(role, shard)
  pool_config&.pool
end


  








  

    #set_pool_manager(connection_name)   (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 279



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