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

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

|
+-- Book
|    |
|    +-- ScaryBook
|    +-- GoodBook
+-- Author
+-- BankAccount

Suppose that Book is to connect to a separate database (i.e. one other than the default database). Then Book, ScaryBook and GoodBook will all use the same connection pool. Likewise, Author and BankAccount will use the same connection pool. However, the connection pool used by Author/BankAccount is not the same as the one used by Book/ScaryBook/GoodBook.

Normally there is only a single ConnectionHandler instance, accessible via ActiveRecord::Base.connection_handler. Active Record models use this to determine that connection pool that they should use.

Methods
A
C
E
N
R
Attributes
[R] connection_pools
Class Public methods
new(pools = {})

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 368
def initialize(pools = {})
  @connection_pools = pools
end
Instance Public methods
active_connections?()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 378
def active_connections?
  connection_pools.values.any? { |pool| pool.active_connection? }
end
clear_active_connections!()

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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 385
def clear_active_connections!
  @connection_pools.each_value {|pool| pool.release_connection }
end
clear_all_connections!()

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 394
def clear_all_connections!
  @connection_pools.each_value {|pool| pool.disconnect! }
end
clear_reloadable_connections!()

Clears the cache which maps classes.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 390
def clear_reloadable_connections!
  @connection_pools.each_value {|pool| pool.clear_reloadable_connections! }
end
connected?(klass)

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 414
def connected?(klass)
  conn = retrieve_connection_pool(klass)
  conn && conn.connected?
end
establish_connection(name, spec)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 372
def establish_connection(name, spec)
  @connection_pools[name] = ConnectionAdapters::ConnectionPool.new(spec)
end
remove_connection(klass)

Remove the connection for this class. This will close the active connection and the defined connection (if they exist). The result can be used as an argument for establish_connection, for easily re-establishing the connection.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 423
def remove_connection(klass)
  pool = @connection_pools[klass.name]
  return nil unless pool

  pool.automatic_reconnect = false
  pool.disconnect!
  pool.spec.config
end
retrieve_connection_pool(klass)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 432
def retrieve_connection_pool(klass)
  pool = @connection_pools[klass.name]
  return pool if pool
  return nil if ActiveRecord::Base == klass
  retrieve_connection_pool klass.superclass
end