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 266
    def clear_query_caches_for_current_thread
      if ActiveRecord.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
🔎 See on GitHub

connected?()

Returns true if Active Record is connected.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 317
    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 137
    def connected_to(role: nil, shard: nil, prevent_writes: false, &blk)
      if ActiveRecord.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

      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.

ActiveRecord::Base.connected_to(role: :writing) do
  ActiveRecord::Base.connected_to?(role: :writing) #=> true
  ActiveRecord::Base.connected_to?(role: :reading) #=> false
end
📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 252
    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 172
    def connected_to_many(*classes, role:, shard: nil, prevent_writes: false)
      classes = classes.flatten

      if ActiveRecord.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 == 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 198
    def connecting_to(role: default_role, shard: default_shard, prevent_writes: false)
      if ActiveRecord.legacy_connection_handling
        raise NotImplementedError, "`connecting_to` is not available with `legacy_connection_handling`."
      end

      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()

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.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 279
    def connection
      retrieve_connection
    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: "db/development.sqlite3", adapter: "sqlite3"}>

Use only for reading.

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 304
    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 308
    def connection_pool
      connection_handler.retrieve_connection_pool(connection_specification_name, role: current_role, shard: current_shard) || raise(ConnectionNotEstablished)
    end
🔎 See on GitHub

connection_specification_name()

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

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 286
    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
🔎 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 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.

📝 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 = []

      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
🔎 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 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
🔎 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 214
    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

remove_connection(name = nil)

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 321
    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
🔎 See on GitHub

retrieve_connection()

📝 Source code 
# File activerecord/lib/active_record/connection_handling.rb, line 312
    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 223
    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 238
    def while_preventing_writes(enabled = true, &block)
      if ActiveRecord.legacy_connection_handling
        connection_handler.while_preventing_writes(enabled, &block)
      else
        connected_to(role: current_role, prevent_writes: enabled, &block)
      end
    end
🔎 See on GitHub