index
Methods
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Constants
DEFAULT_ENV = -> { RAILS_ENV.call || "default_env" }
 
RAILS_ENV = -> { (Rails.env if defined?(Rails.env)) || ENV["RAILS_ENV"].presence || ENV["RACK_ENV"].presence }
 
Attributes
[W] connection_specification_name
Instance Public methods
clear_query_caches_for_current_thread()

Clears the query cache for all connections associated with the current thread.

# File activerecord/lib/active_record/connection_handling.rb, line 269
def clear_query_caches_for_current_thread
  if ActiveRecord::Base.legacy_connection_handling
    ActiveRecord::Base.connection_handlers.each_value do |handler|
      clear_on_handler(handler)
    end
  else
    clear_on_handler(ActiveRecord::Base.connection_handler)
  end
end
connected?()

Returns true if Active Record is connected.

# File activerecord/lib/active_record/connection_handling.rb, line 331
def connected?
  connection_handler.connected?(connection_specification_name, role: current_role, shard: current_shard)
end
connected_to(database: nil, role: nil, shard: nil, prevent_writes: false, &blk)

Connects to a role (ex writing, reading or a custom role) and/or shard for the duration of the block. At the end of the block the connection will be returned to the original role / shard.

If only a role is passed, Active Record will look up the connection based on the requested role. If a non-established role is requested an ActiveRecord::ConnectionNotEstablished error will be raised:

ActiveRecord::Base.connected_to(role: :writing) do
  Dog.create! # creates dog using dog writing connection
end

ActiveRecord::Base.connected_to(role: :reading) do
  Dog.create! # throws exception because we're on a replica
end

When swapping to a shard, the role must be passed as well. If a non-existent shard is passed, an ActiveRecord::ConnectionNotEstablished error will be raised.

When a shard and role is passed, Active Record will first lookup the role, and then look up the connection by shard key.

ActiveRecord::Base.connected_to(role: :reading, shard: :shard_one_replica) do
  Dog.first # finds first Dog record stored on the shard one replica
end

The database kwarg is deprecated and will be removed in 6.2.0 without replacement.

# File activerecord/lib/active_record/connection_handling.rb, line 139
def connected_to(database: nil, role: nil, shard: nil, prevent_writes: false, &blk)
  if legacy_connection_handling
    if self != Base
      raise NotImplementedError, "`connected_to` can only be called on ActiveRecord::Base with legacy connection handling."
    end
  else
    if self != Base && !abstract_class
      raise NotImplementedError, "calling `connected_to` is only allowed on ActiveRecord::Base or abstract classes."
    end

    if name != connection_specification_name && !primary_class?
      raise NotImplementedError, "calling `connected_to` is only allowed on the abstract class that established the connection."
    end
  end

  if database && (role || shard)
    raise ArgumentError, "`connected_to` cannot accept a `database` argument with any other arguments."
  elsif database
    ActiveSupport::Deprecation.warn("The database key in `connected_to` is deprecated. It will be removed in Rails 6.2.0 without replacement.")

    if database.is_a?(Hash)
      role, database = database.first
      role = role.to_sym
    end

    db_config, owner_name = resolve_config_for_connection(database)
    handler = lookup_connection_handler(role)

    handler.establish_connection(db_config, owner_name: owner_name, role: role)

    with_handler(role, &blk)
  elsif role || shard
    unless role
      raise ArgumentError, "`connected_to` cannot accept a `shard` argument without a `role`."
    end

    with_role_and_shard(role, shard, prevent_writes, &blk)
  else
    raise ArgumentError, "must provide a `shard` and/or `role`."
  end
end
connected_to?(role:, shard: ActiveRecord::Base.default_shard)

Returns true if role is the current connected role.

ActiveRecord::Base.connected_to(role: :writing) do
  ActiveRecord::Base.connected_to?(role: :writing) #=> true
  ActiveRecord::Base.connected_to?(role: :reading) #=> false
end
# File activerecord/lib/active_record/connection_handling.rb, line 255
def connected_to?(role:, shard: ActiveRecord::Base.default_shard)
  current_role == role.to_sym && current_shard == shard.to_sym
end
connected_to_many(*classes, role:, shard: nil, prevent_writes: false)

Connects a role and/or shard to the provided connection names. Optionally prevent_writes can be passed to block writes on a connection. reading will automatically set prevent_writes to true.

connected_to_many is an alternative to deeply nested connected_to blocks.

Usage:

ActiveRecord::Base.connected_to_many(AnimalsRecord, MealsRecord, role: :reading) do
  Dog.first # Read from animals replica
  Dinner.first # Read from meals replica
  Person.first # Read from primary writer
end
# File activerecord/lib/active_record/connection_handling.rb, line 194
def connected_to_many(*classes, role:, shard: nil, prevent_writes: false)
  classes = classes.flatten

  if legacy_connection_handling
    raise NotImplementedError, "connected_to_many is not available with legacy connection handling"
  end

  if self != Base || classes.include?(Base)
    raise NotImplementedError, "connected_to_many can only be called on ActiveRecord::Base."
  end

  prevent_writes = true if role == reading_role

  connected_to_stack << { role: role, shard: shard, prevent_writes: prevent_writes, klasses: classes }
  yield
ensure
  connected_to_stack.pop
end
connecting_to(role: default_role, shard: default_shard, prevent_writes: false)

Use a specified connection.

This method is useful for ensuring that a specific connection is being used. For example, when booting a console in readonly mode.

It is not recommended to use this method in a request since it does not yield to a block like connected_to.

# File activerecord/lib/active_record/connection_handling.rb, line 220
def connecting_to(role: default_role, shard: default_shard, prevent_writes: false)
  if legacy_connection_handling
    raise NotImplementedError, "`connecting_to` is not available with `legacy_connection_handling`."
  end

  prevent_writes = true if role == reading_role

  self.connected_to_stack << { role: role, shard: shard, prevent_writes: prevent_writes, klasses: [self] }
end
connection()

Returns the connection currently associated with the class. This can also be used to “borrow” the connection to do database work unrelated to any of the specific Active Records.

# File activerecord/lib/active_record/connection_handling.rb, line 282
def connection
  retrieve_connection
end
connection_config()

Returns the configuration of the associated connection as a hash:

ActiveRecord::Base.connection_config
# => {pool: 5, timeout: 5000, database: "db/development.sqlite3", adapter: "sqlite3"}

Please use only for reading.

# File activerecord/lib/active_record/connection_handling.rb, line 306
def connection_config
  connection_pool.db_config.configuration_hash
end
connection_db_config()

Returns the db_config object from the associated connection:

ActiveRecord::Base.connection_db_config
  #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fd1acbded10 @env_name="development",
    @name="primary", @config={pool: 5, timeout: 5000, database: "db/development.sqlite3", adapter: "sqlite3"}>

Use only for reading.

# File activerecord/lib/active_record/connection_handling.rb, line 318
def connection_db_config
  connection_pool.db_config
end
connection_pool()
# File activerecord/lib/active_record/connection_handling.rb, line 322
def connection_pool
  connection_handler.retrieve_connection_pool(connection_specification_name, role: current_role, shard: current_shard) || raise(ConnectionNotEstablished)
end
connection_specification_name()

Return the connection specification name from the current class or its parent.

# File activerecord/lib/active_record/connection_handling.rb, line 289
def connection_specification_name
  if !defined?(@connection_specification_name) || @connection_specification_name.nil?
    return self == Base ? Base.name : superclass.connection_specification_name
  end
  @connection_specification_name
end
connects_to(database: {}, shards: {})

Connects a model to the databases specified. The database keyword takes a hash consisting of a role and a database_key.

This will create a connection handler for switching between connections, look up the config hash using the database_key and finally establishes a connection to that config.

class AnimalsModel < ApplicationRecord
  self.abstract_class = true

  connects_to database: { writing: :primary, reading: :primary_replica }
end

connects_to also supports horizontal sharding. The horizontal sharding API also supports read replicas. Connect a model to a list of shards like this:

class AnimalsModel < ApplicationRecord
  self.abstract_class = true

  connects_to shards: {
    default: { writing: :primary, reading: :primary_replica },
    shard_two: { writing: :primary_shard_two, reading: :primary_shard_replica_two }
  }
end

Returns an array of database connections.

# File activerecord/lib/active_record/connection_handling.rb, line 81
def connects_to(database: {}, shards: {})
  raise NotImplementedError, "`connects_to` can only be called on ActiveRecord::Base or abstract classes" unless self == Base || abstract_class?

  if database.present? && shards.present?
    raise ArgumentError, "`connects_to` can only accept a `database` or `shards` argument, but not both arguments."
  end

  connections = []

  database.each do |role, database_key|
    db_config, owner_name = resolve_config_for_connection(database_key)
    handler = lookup_connection_handler(role.to_sym)

    self.connection_class = true
    connections << handler.establish_connection(db_config, owner_name: owner_name, role: role)
  end

  shards.each do |shard, database_keys|
    database_keys.each do |role, database_key|
      db_config, owner_name = resolve_config_for_connection(database_key)
      handler = lookup_connection_handler(role.to_sym)

      self.connection_class = true
      connections << handler.establish_connection(db_config, owner_name: owner_name, role: role, shard: shard.to_sym)
    end
  end

  connections
end
establish_connection(config_or_env = nil)

Establishes the connection to the database. Accepts a hash as input where the :adapter key must be specified with the name of a database adapter (in lower-case) example for regular databases (MySQL, PostgreSQL, etc):

ActiveRecord::Base.establish_connection(
  adapter:  "mysql2",
  host:     "localhost",
  username: "myuser",
  password: "mypass",
  database: "somedatabase"
)

Example for SQLite database:

ActiveRecord::Base.establish_connection(
  adapter:  "sqlite3",
  database: "path/to/dbfile"
)

Also accepts keys as strings (for parsing from YAML for example):

ActiveRecord::Base.establish_connection(
  "adapter"  => "sqlite3",
  "database" => "path/to/dbfile"
)

Or a URL:

ActiveRecord::Base.establish_connection(
  "postgres://myuser:mypass@localhost/somedatabase"
)

In case ActiveRecord::Base.configurations is set (Rails automatically loads the contents of config/database.yml into it), a symbol can also be given as argument, representing a key in the configuration hash:

ActiveRecord::Base.establish_connection(:production)

The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError may be returned on an error.

# File activerecord/lib/active_record/connection_handling.rb, line 49
def establish_connection(config_or_env = nil)
  config_or_env ||= DEFAULT_ENV.call.to_sym
  db_config, owner_name = resolve_config_for_connection(config_or_env)
  connection_handler.establish_connection(db_config, owner_name: owner_name, role: current_role, shard: current_shard)
end
remove_connection(name = nil)
# File activerecord/lib/active_record/connection_handling.rb, line 335
def remove_connection(name = nil)
  name ||= @connection_specification_name if defined?(@connection_specification_name)
  # if removing a connection that has a pool, we reset the
  # connection_specification_name so it will use the parent
  # pool.
  if connection_handler.retrieve_connection_pool(name, role: current_role, shard: current_shard)
    self.connection_specification_name = nil
  end

  connection_handler.remove_connection_pool(name, role: current_role, shard: current_shard)
end
retrieve_connection()
# File activerecord/lib/active_record/connection_handling.rb, line 326
def retrieve_connection
  connection_handler.retrieve_connection(connection_specification_name, role: current_role, shard: current_shard)
end
while_preventing_writes(enabled = true, &block)

Prevent writing to the database regardless of role.

In some cases you may want to prevent writes to the database even if you are on a database that can write. while_preventing_writes will prevent writes to the database for the duration of the block.

This method does not provide the same protection as a readonly user and is meant to be a safeguard against accidental writes.

See READ_QUERY for the queries that are blocked by this method.

# File activerecord/lib/active_record/connection_handling.rb, line 241
def while_preventing_writes(enabled = true, &block)
  if legacy_connection_handling
    connection_handler.while_preventing_writes(enabled, &block)
  else
    connected_to(role: current_role, prevent_writes: enabled, &block)
  end
end