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Active Record 连接处理程序

ConnectionHandler 是 ConnectionPool 对象的集合。它用于维护连接到不同数据库的独立连接池。

例如，假设您有 5 个模型，具有以下层次结构

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

以及一个类似于此的 database.yml

development:
  database: my_application
  host: localhost

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

您在开发环境中的主数据库是“my_application”，但 Book 模型连接到一个名为“library_db”的独立数据库（这甚至可以是不同机器上的数据库）。

Book、ScaryBook 和 GoodBook 都将使用相同的连接池连接到“library_db”，而 Author、BankAccount 以及您创建的任何其他模型都将使用默认连接池连接到“my_application”。

各种连接池由 ConnectionHandler 的单个实例管理，可以通过 ActiveRecord::Base.connection_handler 访问。所有 Active Record 模型都使用此处理程序来确定它们应该使用的连接池。

ConnectionHandler 类没有与 Active 模型耦合，因为它不知道模型。模型需要向处理程序传递连接规范名称，以便查找正确的连接池。

方法
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类公共方法

new()

来源: 显示 | 在 GitHub 上 

# 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

实例公共方法

active_connections?(role = nil)

如果 ConnectionHandler 管理的连接池中存在任何活动连接，则返回 true。

来源: 显示 | 在 GitHub 上 

# 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()

来源: 显示 | 在 GitHub 上 

# 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)

将当前线程正在使用的任何连接返回到池中，并将不再活动的线程缓存的连接也返回到池中。

来源: 显示 | 在 GitHub 上 

# 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)

来源: 显示 | 在 GitHub 上 

# 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)

清除映射类的缓存。

有关详细信息，请参阅 ConnectionPool#clear_reloadable_connections!。

来源：显示 | 在 GitHub 上 

# 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)

如果此类可访问的连接已打开，则返回 true。

来源：显示 | 在 GitHub 上 

# 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)

返回连接处理程序和给定角色的池。如果传递了 :all，则将返回属于连接处理程序的所有池。

也称为：connection_pools

来源：显示 | 在 GitHub 上 

# 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_pools(role = nil)

别名：connection_pool_list

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

来源：显示 | 在 GitHub 上 

# 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)

断开所有当前空闲的连接。

有关详细信息，请参阅 ConnectionPool#flush!。

来源：显示 | 在 GitHub 上 

# 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

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

来源：显示 | 在 GitHub 上 

# 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

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

检索连接池的操作非常频繁，因此我们将其缓存到 @connection_name_to_pool_manager 中。这使得在进程预热后检索连接池成为 O(1) 操作。当建立或移除连接时，我们会使缓存失效。

来源：显示 | 在 GitHub 上 

# 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