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_query_caches_for_current_thread()

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

📝 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.clear_query_cache
      end
    end
🔎 See on GitHub

connected?()

Returns true if Active Record is connected.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 337
    def connected?
      connection_handler.connected?(connection_specification_name, role: current_role, shard: current_shard)
    end
🔎 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
📝 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
🔎 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
📝 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
🔎 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
📝 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
🔎 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.

📝 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
🔎 See on GitHub

connection()

Soft deprecated. Use #with_connection or #lease_connection instead.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 260
    def connection
      pool = connection_pool
      if pool.permanent_lease?
        case ActiveRecord.permanent_connection_checkout
        when :deprecated
          ActiveRecord.deprecator.warn <<~MESSAGE
            Called deprecated `ActiveRecord::Base.connection` method.

            Either use `with_connection` or `lease_connection`.
          MESSAGE
        when :disallowed
          raise ActiveRecordError, <<~MESSAGE
            Called deprecated `ActiveRecord::Base.connection` method.

            Either use `with_connection` or `lease_connection`.
          MESSAGE
        end
        pool.lease_connection
      else
        pool.active_connection
      end
    end
🔎 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.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 320
    def connection_db_config
      connection_pool.db_config
    end
🔎 See on GitHub

connection_pool()

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 328
    def connection_pool
      connection_handler.retrieve_connection_pool(connection_specification_name, role: current_role, shard: current_shard, strict: true)
    end
🔎 See on GitHub

connection_specification_name()

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

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 302
    def connection_specification_name
      if @connection_specification_name.nil?
        return self == Base ? Base.name : superclass.connection_specification_name
      end
      @connection_specification_name
    end
🔎 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.

📝 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
🔎 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.

📝 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
🔎 See on GitHub

lease_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. The connection will remain leased for the entire duration of the request or job, or until #release_connection is called.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 255
    def lease_connection
      connection_pool.lease_connection
    end
🔎 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.

📝 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
🔎 See on GitHub

release_connection()

Return the currently leased connection into the pool

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 284
    def release_connection
      connection_pool.release_connection
    end
🔎 See on GitHub

remove_connection()

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 341
    def remove_connection
      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
🔎 See on GitHub

retrieve_connection()

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 332
    def retrieve_connection
      connection_handler.retrieve_connection(connection_specification_name, role: current_role, shard: current_shard)
    end
🔎 See on GitHub

shard_swapping_prohibited?()

Determine whether or not shard swapping is currently prohibited

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 206
    def shard_swapping_prohibited?
      ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping]
    end
🔎 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.

📝 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
🔎 See on GitHub

with_connection(prevent_permanent_checkout: false, &block)

Checkouts a connection from the pool, yield it and then check it back in. If a connection was already leased via lease_connection or a parent call to with_connection, that same connection is yieled. If lease_connection is called inside the block, the connection won’t be checked back in. If connection is called inside the block, the connection won’t be checked back in unless the prevent_permanent_checkout argument is set to true.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 295
    def with_connection(prevent_permanent_checkout: false, &block)
      connection_pool.with_connection(prevent_permanent_checkout: prevent_permanent_checkout, &block)
    end
🔎 See on GitHub