ConnectionHandler is a collection of ConnectionPool objects. It is used for keeping separate connection pools for ActiveRecord 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. ActiveRecord models use this to determine that connection pool that they should use.

Methods
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Class Public methods
new(pools = {})
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 287
def initialize(pools = {})
  @connection_pools = pools
end
Instance Public methods
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.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 302
def clear_active_connections!
  @connection_pools.each_value {|pool| pool.release_connection }
end
clear_all_connections!()
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 311
def clear_all_connections!
  @connection_pools.each_value {|pool| pool.disconnect! }
end
clear_reloadable_connections!()

Clears the cache which maps classes

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 307
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.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 331
def connected?(klass)
  conn = retrieve_connection_pool(klass)
  conn ? conn.connected? : false
end
connection_pools()
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 291
def connection_pools
  @connection_pools ||= {}
end
establish_connection(name, spec)
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 295
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.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 340
def remove_connection(klass)
  pool = @connection_pools[klass.name]
  @connection_pools.delete_if { |key, value| value == pool }
  pool.disconnect! if pool
  pool.spec.config if pool
end
retrieve_connection_pool(klass)
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 347
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