module ActiveRecord::ConnectionHandling

clear_active_connections! (role = nil)

# File activerecord/lib/active_record/connection_handling.rb, line 319
def clear_active_connections!(role = nil)
  deprecation_for_delegation(__method__)
  connection_handler.clear_active_connections!(role)
end

clear_all_connections! (role = nil)

# File activerecord/lib/active_record/connection_handling.rb, line 329
def clear_all_connections!(role = nil)
  deprecation_for_delegation(__method__)
  connection_handler.clear_all_connections!(role)
end

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 244
def clear_query_caches_for_current_thread
  connection_handler.each_connection_pool do |pool|
    pool.connection.clear_query_cache if pool.active_connection?
  end
end

clear_reloadable_connections! (role = nil)

# File activerecord/lib/active_record/connection_handling.rb, line 324
def clear_reloadable_connections!(role = nil)
  deprecation_for_delegation(__method__)
  connection_handler.clear_reloadable_connections!(role)
end

connected? ()

Returns true if Active Record is connected.

# File activerecord/lib/active_record/connection_handling.rb, line 291
def connected?
  connection_handler.connected?(connection_specification_name, role: current_role, shard: current_shard)
end

connected_to (role: nil, shard: nil, prevent_writes: false, &blk)

Connects to a role (e.g. 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

# File activerecord/lib/active_record/connection_handling.rb, line 134
def connected_to(role: nil, shard: nil, prevent_writes: false, &blk)
  if self != Base && !abstract_class
    raise NotImplementedError, "calling `connected_to` is only allowed on ActiveRecord::Base or abstract classes."
  end

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

  unless role || shard
    raise ArgumentError, "must provide a `shard` and/or `role`."
  end

  with_role_and_shard(role, shard, prevent_writes, &blk)
end

connected_to? (role:, shard: ActiveRecord::Base.default_shard)

Returns true if role is the current connected role and/or current connected shard. If no shard is passed, the default will be used.

ActiveRecord::Base.connected_to(role: :writing) do
  ActiveRecord::Base.connected_to?(role: :writing) #=> true
  ActiveRecord::Base.connected_to?(role: :reading) #=> false
end

ActiveRecord::Base.connected_to(role: :reading, shard: :shard_one) do
  ActiveRecord::Base.connected_to?(role: :reading, shard: :shard_one) #=> true
  ActiveRecord::Base.connected_to?(role: :reading, shard: :default) #=> false
  ActiveRecord::Base.connected_to?(role: :writing, shard: :shard_one) #=> true
end

# File activerecord/lib/active_record/connection_handling.rb, line 239
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 163
def connected_to_many(*classes, role:, shard: nil, prevent_writes: false)
  classes = classes.flatten

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

  prevent_writes = true if role == ActiveRecord.reading_role

  append_to_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 185
def connecting_to(role: default_role, shard: default_shard, prevent_writes: false)
  prevent_writes = true if role == ActiveRecord.reading_role

  append_to_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 253
def connection
  retrieve_connection
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: "storage/development.sqlite3", adapter: "sqlite3"}>

Use only for reading.

# File activerecord/lib/active_record/connection_handling.rb, line 278
def connection_db_config
  connection_pool.db_config
end

connection_pool ()

# File activerecord/lib/active_record/connection_handling.rb, line 282
def connection_pool
  connection_handler.retrieve_connection_pool(connection_specification_name, role: current_role, shard: current_shard) || raise(ConnectionNotEstablished)
end

connection_specification_name ()

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

# File activerecord/lib/active_record/connection_handling.rb, line 260
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 look up the database config using the database_key and establish 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 supports read replicas as well. You can 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 = []

  if shards.empty?
    shards[:default] = database
  end

  self.default_shard = shards.keys.first

  shards.each do |shard, database_keys|
    database_keys.each do |role, database_key|
      db_config = resolve_config_for_connection(database_key)

      self.connection_class = true
      connections << connection_handler.establish_connection(db_config, owner_name: self, 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 50
def establish_connection(config_or_env = nil)
  config_or_env ||= DEFAULT_ENV.call.to_sym
  db_config = resolve_config_for_connection(config_or_env)
  connection_handler.establish_connection(db_config, owner_name: self, role: current_role, shard: current_shard)
end

flush_idle_connections! (role = nil)

# File activerecord/lib/active_record/connection_handling.rb, line 334
def flush_idle_connections!(role = nil)
  deprecation_for_delegation(__method__)
  connection_handler.flush_idle_connections!(role)
end

prohibit_shard_swapping (enabled = true) { || ... }

Prohibit swapping shards while inside of the passed block.

In some cases you may want to be able to swap shards but not allow a nested call to connected_to or connected_to_many to swap again. This is useful in cases you’re using sharding to provide per-request database isolation.

# File activerecord/lib/active_record/connection_handling.rb, line 197
def prohibit_shard_swapping(enabled = true)
  prev_value = ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping]
  ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping] = enabled
  yield
ensure
  ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping] = prev_value
end

remove_connection (name = nil)

# File activerecord/lib/active_record/connection_handling.rb, line 295
    def remove_connection(name = nil)
      if name
        ActiveRecord.deprecator.warn(<<-MSG.squish)
          The name argument for `#remove_connection` is deprecated without replacement
          and will be removed in Rails 7.2. `#remove_connection` should always be called
          on the connection class directly, which makes the name argument obsolete.
        MSG
      end

      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 286
def retrieve_connection
  connection_handler.retrieve_connection(connection_specification_name, role: current_role, shard: current_shard)
end

shard_swapping_prohibited? ()

Determine whether or not shard swapping is currently prohibited

# File activerecord/lib/active_record/connection_handling.rb, line 206
def shard_swapping_prohibited?
  ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping]
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 221
def while_preventing_writes(enabled = true, &block)
  connected_to(role: current_role, prevent_writes: enabled, &block)
end

Active Record Connection Handling¶ ↑

Constants

Attributes

Public Instance Methods