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Class Public methods
new() Link
Instance Public methods
add_transaction_record(record, ensure_finalize = true) Link
Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.
begin_db_transaction() Link
Begins the transaction (and turns off auto-committing).
begin_isolated_db_transaction(isolation) Link
Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.
commit_db_transaction() Link
Commits the transaction (and turns on auto-committing).
create(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil) Link
default_sequence_name(table, column) Link
delete(arel, name = nil, binds = []) Link
Executes the delete statement and returns the number of rows affected.
empty_insert_statement_value(primary_key = nil) Link
exec_delete(sql, name = nil, binds = []) Link
Executes delete sql
statement in the context of this connection using binds
as the bind substitutes. name
is logged along with the executed sql
statement.
exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil, returning: nil) Link
Executes insert sql
statement in the context of this connection using binds
as the bind substitutes. name
is logged along with the executed sql
statement. Some adapters support the ‘returning` keyword argument which allows to control the result of the query: `nil` is the default value and maintains default behavior. If an array of column names is passed - the result will contain values of the specified columns from the inserted row.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 157 def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil, returning: nil) sql, binds = sql_for_insert(sql, pk, binds, returning) internal_exec_query(sql, name, binds) end
exec_query(sql, name = "SQL", binds = [], prepare: false) Link
Executes sql
statement in the context of this connection using binds
as the bind substitutes. name
is logged along with the executed sql
statement.
Note: the query is assumed to have side effects and the query cache will be cleared. If the query is read-only, consider using select_all
instead.
exec_update(sql, name = nil, binds = []) Link
Executes update sql
statement in the context of this connection using binds
as the bind substitutes. name
is logged along with the executed sql
statement.
execute(sql, name = nil, allow_retry: false) Link
Executes the SQL statement in the context of this connection and returns the raw result from the connection adapter.
Setting allow_retry
to true causes the db to reconnect and retry executing the SQL statement in case of a connection-related exception. This option should only be enabled for known idempotent queries.
Note: the query is assumed to have side effects and the query cache will be cleared. If the query is read-only, consider using select_all
instead.
Note: depending on your database connector, the result returned by this method may be manually memory managed. Consider using exec_query
wrapper instead.
high_precision_current_timestamp() Link
Returns an Arel
SQL literal for the CURRENT_TIMESTAMP for usage with arbitrary precision date/time columns.
Adapters supporting datetime with precision should override this to provide as much precision as is available.
insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil) Link
Executes an INSERT query and returns the new record’s ID
id_value
will be returned unless the value is nil
, in which case the database will attempt to calculate the last inserted id and return that value.
If the next id was calculated in advance (as in Oracle), it should be passed in as id_value
. Some adapters support the ‘returning` keyword argument which allows defining the return value of the method: `nil` is the default value and maintains default behavior. If an array of column names is passed - an array of is returned from the method representing values of the specified columns from the inserted row.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 195 def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil) sql, binds = to_sql_and_binds(arel, binds) value = exec_insert(sql, name, binds, pk, sequence_name, returning: returning) return returning_column_values(value) unless returning.nil? id_value || last_inserted_id(value) end
insert_fixture(fixture, table_name) Link
Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (e.g. Oracle). Most of adapters should implement insert_fixtures_set
that leverages bulk SQL insert. We keep this method to provide fallback for databases like SQLite that do not support bulk inserts.
insert_fixtures_set(fixture_set, tables_to_delete = []) Link
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 486 def insert_fixtures_set(fixture_set, tables_to_delete = []) fixture_inserts = build_fixture_statements(fixture_set) table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name(table)}" } statements = table_deletes + fixture_inserts transaction(requires_new: true) do disable_referential_integrity do execute_batch(statements, "Fixtures Load") end end end
reset_isolation_level() Link
Hook point called after an isolated DB transaction is committed or rolled back. Most adapters don’t need to implement anything because the isolation level is set on a per transaction basis. But some databases like SQLite set it on a per connection level and need to explicitly reset it after commit or rollback.
reset_sequence!(table, column, sequence = nil) Link
Set the sequence to the max value of the table’s column.
restart_db_transaction() Link
rollback_db_transaction() Link
Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 450 def rollback_db_transaction exec_rollback_db_transaction rescue ActiveRecord::ConnectionNotEstablished, ActiveRecord::ConnectionFailed # Connection's gone; that counts as a rollback end
rollback_to_savepoint(name = nil) Link
sanitize_limit(limit) Link
select_all(arel, name = nil, binds = [], preparable: nil, async: false, allow_retry: false) Link
Returns an ActiveRecord::Result
instance.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 69 def select_all(arel, name = nil, binds = [], preparable: nil, async: false, allow_retry: false) arel = arel_from_relation(arel) sql, binds, preparable, allow_retry = to_sql_and_binds(arel, binds, preparable, allow_retry) select(sql, name, binds, prepare: prepared_statements && preparable, async: async && FutureResult::SelectAll, allow_retry: allow_retry ) rescue ::RangeError ActiveRecord::Result.empty(async: async) end
select_one(arel, name = nil, binds = [], async: false) Link
Returns a record hash with the column names as keys and column values as values.
select_rows(arel, name = nil, binds = [], async: false) Link
Returns an array of arrays containing the field values. Order is the same as that returned by columns
.
select_value(arel, name = nil, binds = [], async: false) Link
Returns a single value from a record
select_values(arel, name = nil, binds = []) Link
Returns an array of the values of the first column in a select:
select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
to_sql(arel_or_sql_string, binds = []) Link
Converts an arel AST to SQL
transaction(requires_new: nil, isolation: nil, &block) Link
Runs the given block in a database transaction, and returns the result of the block.
Transaction
callbacks
transaction
yields an ActiveRecord::Transaction
object on which it is possible to register callback:
ActiveRecord::Base.transaction do |transaction|
transaction.before_commit { puts "before commit!" }
transaction.after_commit { puts "after commit!" }
transaction.after_rollback { puts "after rollback!" }
end
Nested transactions support
transaction
calls can be nested. By default, this makes all database statements in the nested transaction block become part of the parent transaction. For example, the following behavior may be surprising:
ActiveRecord::Base.transaction do
Post.create(title: 'first')
ActiveRecord::Base.transaction do
Post.create(title: 'second')
raise ActiveRecord::Rollback
end
end
This creates both “first” and “second” posts. Reason is the ActiveRecord::Rollback
exception in the nested block does not issue a ROLLBACK. Since these exceptions are captured in transaction blocks, the parent block does not see it and the real transaction is committed.
Most databases don’t support true nested transactions. At the time of writing, the only database that supports true nested transactions that we’re aware of, is MS-SQL.
In order to get around this problem, transaction
will emulate the effect of nested transactions, by using savepoints: dev.mysql.com/doc/refman/en/savepoint.html.
It is safe to call this method if a database transaction is already open, i.e. if transaction
is called within another transaction
block. In case of a nested call, transaction
will behave as follows:
-
The block will be run without doing anything. All database statements that happen within the block are effectively appended to the already open database transaction.
-
However, if
:requires_new
is set, the block will be wrapped in a database savepoint acting as a sub-transaction.
In order to get a ROLLBACK for the nested transaction you may ask for a real sub-transaction by passing requires_new: true
. If anything goes wrong, the database rolls back to the beginning of the sub-transaction without rolling back the parent transaction. If we add it to the previous example:
ActiveRecord::Base.transaction do
Post.create(title: 'first')
ActiveRecord::Base.transaction(requires_new: true) do
Post.create(title: 'second')
raise ActiveRecord::Rollback
end
end
only post with title “first” is created.
See ActiveRecord::Transactions
to learn more.
Caveats
MySQL
doesn’t support DDL transactions. If you perform a DDL operation, then any created savepoints will be automatically released. For example, if you’ve created a savepoint, then you execute a CREATE TABLE statement, then the savepoint that was created will be automatically released.
This means that, on MySQL
, you shouldn’t execute DDL operations inside a transaction
call that you know might create a savepoint. Otherwise, transaction
will raise exceptions when it tries to release the already-automatically-released savepoints:
Model.lease_connection.transaction do # BEGIN
Model.lease_connection.transaction(requires_new: true) do # CREATE SAVEPOINT active_record_1
Model.lease_connection.create_table(...)
# active_record_1 now automatically released
end # RELEASE SAVEPOINT active_record_1 <--- BOOM! database error!
end
Transaction
isolation
If your database supports setting the isolation level for a transaction, you can set it like so:
Post.transaction(isolation: :serializable) do
# ...
end
Valid isolation levels are:
-
:read_uncommitted
-
:read_committed
-
:repeatable_read
-
:serializable
You should consult the documentation for your database to understand the semantics of these different levels:
An ActiveRecord::TransactionIsolationError
will be raised if:
-
The adapter does not support setting the isolation level
-
You are joining an existing open transaction
-
You are creating a nested (savepoint) transaction
The mysql2, trilogy, and postgresql adapters support setting the transaction isolation level.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 352 def transaction(requires_new: nil, isolation: nil, joinable: true, &block) if !requires_new && current_transaction.joinable? if isolation raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction" end yield current_transaction.user_transaction else within_new_transaction(isolation: isolation, joinable: joinable, &block) end rescue ActiveRecord::Rollback # rollbacks are silently swallowed end
transaction_isolation_levels() Link
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 420 def transaction_isolation_levels { read_uncommitted: "READ UNCOMMITTED", read_committed: "READ COMMITTED", repeatable_read: "REPEATABLE READ", serializable: "SERIALIZABLE" } end
transaction_open?() Link
truncate(table_name, name = nil) Link
Executes the truncate statement.
update(arel, name = nil, binds = []) Link
Executes the update statement and returns the number of rows affected.