Active Record Connection Handling

Methods

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_active_connections!(role = nil)

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

clear_all_connections!(role = nil)

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

clear_query_caches_for_current_thread()

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

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

clear_reloadable_connections!(role = nil)

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

connected?()

Returns true if Active Record is connected.

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

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
πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

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
πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

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
πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

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.

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

connection()

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

πŸ“ Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 253
    def connection
      retrieve_connection
    end
πŸ”Ž See on GitHub

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.

πŸ“ Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 278
    def connection_db_config
      connection_pool.db_config
    end
πŸ”Ž See on GitHub

connection_pool()

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

connection_specification_name()

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

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

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.

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

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.

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

flush_idle_connections!(role = nil)

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

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.

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

remove_connection(name = nil)

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

retrieve_connection()

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub

shard_swapping_prohibited?()

Determine whether or not shard swapping is currently prohibited

πŸ“ Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 206
    def shard_swapping_prohibited?
      ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping]
    end
πŸ”Ž See on GitHub

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.

πŸ“ Source code 
# 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
πŸ”Ž See on GitHub