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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() Link
Clears the query cache for all connections associated with the current thread.
# 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
connected?() Link
Returns true
if Active Record is connected.
connected_to(role: nil, shard: nil, prevent_writes: false, &blk) Link
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
# 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
connected_to?(role:, shard: ActiveRecord::Base.default_shard) Link
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
connected_to_many(*classes, role:, shard: nil, prevent_writes: false) Link
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 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
connecting_to(role: default_role, shard: default_shard, prevent_writes: false) Link
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 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
connection() Link
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.
connection_db_config() Link
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.
connection_pool() Link
connection_specification_name() Link
Return the connection specification name from the current class or its parent.
# 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
connects_to(database: {}, shards: {}) Link
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 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
establish_connection(config_or_env = nil) Link
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 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
prohibit_shard_swapping(enabled = true) Link
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 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
remove_connection(name = nil) Link
# 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
retrieve_connection() Link
shard_swapping_prohibited?() Link
Determine whether or not shard swapping is currently prohibited
while_preventing_writes(enabled = true, &block) Link
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.
# 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