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Active Record 連線處理器

ConnectionHandler 是收集 ConnectionPool 物件。會用於維護連線到不同資料庫的獨立連線池。

例如，假設您有 5 個模型，其階層如下

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

而 database.yml 如下所示

development:
  database: my_application
  host: localhost

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

開發環境中的主要資料庫為「my_application」，但 Book 模型連線到獨立的資料庫「library_db」（這甚至可能是不同機器上的資料庫）。

Book、ScaryBook 和 GoodBook 都會使用相同的連線池來連線「library_db」，而 Author、BankAccount 和您建立的所有其他模型都將使用預設連線池來連線「my_application」。

這些不同的連線池由透過 ActiveRecord::Base.connection_handler 可存取的單一 ConnectionHandler 執行個體來管理。所有 Active Record 模型使用此處理器來決定應使用的連線池。

ConnectionHandler 類別不會與 Active 模型結合，因為它不了解模型。模塊必須將連線規格名稱傳遞給處理器，才能查閱正確的連線池。

方法
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類別公用方法

new()

來源： 顯示 | 在 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 73
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

執行個體公用方法

active_connections?(role = nil)

如果 ConnectionHandler 正在管理的連線池之間有任何活動連線，則傳回 true。

來源： 顯示 | 在 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 154
def active_connections?(role = nil)
  each_connection_pool(role).any?(&:active_connection?)
end

clear_active_connections!(role = nil)

將目前執行緒使用中任何連線傳回池中，且傳回未執行緒使用、暫存在緩存中的連線至池中。

來源： 顯示 | 在 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 161
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)

來源： 顯示 | 在 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 175
def clear_all_connections!(role = nil)
  each_connection_pool(role).each(&:disconnect!)
end

clear_reloadable_connections!(role = nil)

清除對應類別的快取。

更多資訊，請參閱 ConnectionPool#clear_reloadable_connections!。

原始碼： 顯示 | 於 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 171
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)

如果已開啟可供此類別存取的連線，則傳回 true。

原始碼： 顯示 | 於 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 197
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)

傳回連線處理常式和特定角色的池。如果傳入 :all，則會傳回連線處理常式下的所有池。

別名： connection_pools

原始碼： 顯示 | 於 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 92
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_pools(role = nil)

別名： connection_pool_list

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

原始碼： 顯示 | 於 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 112
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)

中斷所有目前的閒置連線。

更多資訊，請參閱 ConnectionPool#flush!。

原始碼： 顯示 | 於 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 182
def flush_idle_connections!(role = nil)
  each_connection_pool(role).each(&:flush!)
end

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

原始碼： 顯示 | 於 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 202
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, strict: false)

擷取連線池的動作頻率很高，因此我們將它快取在 @connection_name_to_pool_manager 中。這樣一來，只要處理程序是熱的，擷取連線池的動作便能達到 O(1) 的效能。系統會在建立或移除連線時，取消快取。

原始碼： 顯示 | 於 GitHub 上

# File activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb, line 211
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