# 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 Clears the query cache for all connections associated with the current thread.
# 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
Returns true if Active Record is connected.
# 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 Connects to a role (ex 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 252 def connected_to?(role:, shard: ActiveRecord::Base.default_shard) current_role == role.to_sym && current_shard == shard.to_sym end
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
# 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 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 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 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 279 def connection retrieve_connection end
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 304 def connection_db_config connection_pool.db_config end
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.
# 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
# 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 Return the connection specification name from the current class or its parent.
# 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 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.
# 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
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 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
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 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 # 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
# File activerecord/lib/active_record/connection_handling.rb, line 223 def shard_swapping_prohibited? ActiveSupport::IsolatedExecutionState[:active_record_prohibit_shard_swapping] end
Determine whether or not shard swapping is currently prohibited
# 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 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.
© 2004–2021 David Heinemeier Hansson
Licensed under the MIT License.