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Module: ActiveRecord::ConnectionHandling

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Extended In:
Base
Defined in: activerecord/lib/active_record/connection_handling.rb

Constant Summary

Instance Attribute Summary

Instance Method Summary

Instance Attribute Details

#connected? ⇒ Boolean (readonly)

Returns true if Active Record is connected.

[ GitHub ] 

  


# 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


  








  

    #connection_specification_name   (rw)
  



  

    

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


  



  [ GitHub ]


  

  


# 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


  








  

    #connection_specification_name=(value)   (rw)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 299



attr_writer :connection_specification_name


  








  

    #primary_class?  ⇒ Boolean  (readonly)
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 309



def primary_class? # :nodoc:
  self == Base || application_record_class?
end


  








  

    #shard_swapping_prohibited?  ⇒ Boolean  (readonly)
  



  

    

Determine whether or not shard swapping is currently prohibited


  





  


  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 206



def shard_swapping_prohibited?
  ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping]
end


  







Instance Method Details



  

    #adapter_class  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 324



def adapter_class # :nodoc:
  connection_pool.db_config.adapter_class
end


  








  

    #append_to_connected_to_stack(entry)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 383



def append_to_connected_to_stack(entry)
  if shard_swapping_prohibited? && entry[:shard].present?
    raise ArgumentError, "cannot swap `shard` while shard swapping is prohibited."
  end

  connected_to_stack << entry
end


  








  

    #clear_cache!  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 358



def clear_cache! # :nodoc:
  connection_pool.schema_cache.clear!
end


  








  

    #clear_query_caches_for_current_thread  
  



  

    

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


  



  [ GitHub ]


  

  


# 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


  








  

    #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 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 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


  



  [ GitHub ]


  

  


# 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)  ⇒ Boolean 
  



  

    

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


  





  


  [ GitHub ]


  

  


# 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


  



  [ GitHub ]


  

  


# 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.


  



  [ GitHub ]


  

  


# 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  
  



  

    

Soft deprecated. Use #with_connection or #lease_connection instead.


  



  [ GitHub ]


  

  


# 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


  








  

    #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.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 320



def connection_db_config
  connection_pool.db_config
end


  








  

    #connection_pool  
  

  [ GitHub ]


  

  


# 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


  








  

    #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.


  





  
Raises:


    
  
  • 
    (NotImplementedError)
  
    • 





  [ GitHub ]


  

  


# 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.


  



  [ GitHub ]


  

  


# 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


  








  

    #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.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 255



def lease_connection
  connection_pool.lease_connection
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.


  



  [ GitHub ]


  

  


# 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


  








  

    #release_connection  
  



  

    

Return the currently leased connection into the pool


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 284



def release_connection
  connection_pool.release_connection
end


  








  

    #remove_connection  
  

  [ GitHub ]


  

  


# 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


  








  

    #resolve_config_for_connection(config_or_env)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 363



def resolve_config_for_connection(config_or_env)
  raise "Anonymous class is not allowed." unless name

  connection_name = primary_class? ? Base.name : name
  self.connection_specification_name = connection_name

  Base.configurations.resolve(config_or_env)
end


  








  

    #retrieve_connection  
  

  [ GitHub ]


  

  


# 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


  








  

    #schema_cache  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 354



def schema_cache # :nodoc:
  connection_pool.schema_cache
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.


  



  [ GitHub ]


  

  


# 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


  








  

    #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.


  



  [ GitHub ]


  

  


# 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


  








  

    #with_role_and_shard(role, shard, prevent_writes)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/connection_handling.rb', line 372



def with_role_and_shard(role, shard, prevent_writes)
  prevent_writes = true if role == ActiveRecord.reading_role

  append_to_connected_to_stack(role: role, shard: shard, prevent_writes: prevent_writes, klasses: [self])
  return_value = yield
  return_value.load if return_value.is_a? ActiveRecord::Relation
  return_value
ensure
  self.connected_to_stack.pop
end